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Los carburos cementados son materiales formados por granos de carburo y una fase aglutinante. El carburo cementado más conocido es el carburo de wolframio combinado con una fase aglutinante de cobalto WC-Co, pero los investigadores intentan encontrar una alternativa al cobalto, como el níquel, más barato y disponible en mayores cantidades. Los carburos cementados se utilizan principalmente para herramientas de corte por sus excelentes propiedades. El carburo de wolframio tiene una dureza extremadamente alta y la fase aglutinante aumenta la tenacidad del material. Pero estas propiedades dependen de muchos factores, como la composición o la microestructura del material. Las técnicas de caracterización son un medio esencial para comprender la influencia de la microestructura y contribuyen al desarrollo constante de estos materiales esenciales en la industria. La combinación de varios métodos de caracterización, como el estudio del tamaño de grano del carburo y la modelización 3D, se utiliza para comprender el efecto de la microestructura en propiedades mecánicas como la dureza y el módulo elástico. Estos estudios se llevaron a cabo en dos muestras con base de níquel, WC-10Ni y WC-20Ni, con el fin de comprender la importancia de cada tipo de caracterización. Los resultados hallados para ambas muestras mostraron que, a medida que aumentaba la cantidad de fase ligante, disminuían la dureza y el módulo elástico del carburo cementado. El análisis de la estructura tridimensional de los carburos cementados a base de cobalto validó el protocolo ensayado y muestra la importancia de combinar los estudios de superficie y volumen. Este método podría aplicarse posteriormente a muestras de níquel para comparar los resultados experimentales con los teóricos mediante simulaciones numéricas., Cemented carbides are materials made up of carbide grains and a binder phase. The best-known cemented carbide is tungsten carbide combined with a WC-Co cobalt binder phase, but researchers are trying to find an alternative to cobalt, such as nickel, which is cheaper and available in greater quantities. Cemented carbides are mainly used for cutting tools because of their excellent properties. The tungsten carbide has extremely high hardness and the binder phase increases the toughness of the material. But these properties depend on many factors, such as the composition or microstructure of the material. Characterisation techniques are an essential way of understanding the influence of microstructure, and contribute to the constant development of these essential materials in industry. The combination of several characterisation methods, such as the study of carbide grain size and 3D modelling is used to understand the effect of microstructure on mechanical properties such as hardness and Elastic modulus. These studies were carried out on two nickel-based samples, WC-10Ni and WC-20Ni, in order to understand the importance of each type of characterisation. The results found for both samples showed that as the amount of binder phase increased, the hardness and elastic modulus of the cemented carbide decreased. Analysis of the three-dimensional structure of cobalt-based cemented carbides validated the protocol tested and shows the importance of combining surface and volume studies. This method could later be applied to nickel samples to compare experimental results with theoretical ones using numerical simulations., Incoming

This study presents a novel approach for the synthesis of WC-Ni cemented carbides with enhanced mechanical properties. A low-cost solution-based route was used to coat WC powders with well-distributed metallic nickel dots measuring between 17 nm and 39 nm in diameter. Varying compositions with loadings of 2, 6, and 14 vol% Ni were consolidated using spark plasma sintering (SPS) at 1350 degrees C under 50 MPa of uniaxial pressure giving relative densities of 99 +/- 1 %. The sintered WC-Ni cemented carbides had an even distribution of the Ni binder phase in all compositions, with retained ultrafine WC grain sizes of 0.5 +/- 0.1 mu m from the starting powder. The enhanced sinterability of the coated powders allowed for consolidation to near theoretical densities, with a binder content as low as 2 vol%. This is attributed to the uniform distribution of nickel and an extensive Ni-WC interface existing prior to sintering. The small size of the Ni dots likely also contributed to the solid-state sintering starting temperatures of as low as 800 degrees C. The mechanical performance of the resulting cemented carbides was evaluated by measuring the hardness at temperatures between 20 degrees C and 700 degrees C and estimating toughness at room temperature using Vickers indentations. These results showed that the mechanical properties of the WC-Ni cemented carbides synthesised by our method were comparable to conventionally prepared WC-Co cemented carbides with similar grain sizes and binder contents and superior to conventionally prepared WC-Ni cemented carbides. In particular, the 2 vol% Ni composition had excellent hardness at room temperature of up to 2210HV10, while still having an indentation fracture toughness of 7 MPa.m(0.5). Therefore, WC-Ni cemented carbides processed by this novel approach are a promising alternative to conventional WC-Co cemented carbides for a wide range of applications.

This study presents a novel approach for the synthesis of WC-Ni cemented carbides with enhanced mechanical properties. A low-cost solution-based route was used to coat WC powders with well-distributed metallic nickel dots measuring between 17 nm and 39 nm in diameter. Varying compositions with loadings of 2, 6, and 14 vol% Ni were consolidated using spark plasma sintering (SPS) at 1350 degrees C under 50 MPa of uniaxial pressure giving relative densities of 99 +/- 1 %. The sintered WC-Ni cemented carbides had an even distribution of the Ni binder phase in all compositions, with retained ultrafine WC grain sizes of 0.5 +/- 0.1 mu m from the starting powder. The enhanced sinterability of the coated powders allowed for consolidation to near theoretical densities, with a binder content as low as 2 vol%. This is attributed to the uniform distribution of nickel and an extensive Ni-WC interface existing prior to sintering. The small size of the Ni dots likely also contributed to the solid-state sintering starting temperatures of as low as 800 degrees C. The mechanical performance of the resulting cemented carbides was evaluated by measuring the hardness at temperatures between 20 degrees C and 700 degrees C and estimating toughness at room temperature using Vickers indentations. These results showed that the mechanical properties of the WC-Ni cemented carbides synthesised by our method were comparable to conventionally prepared WC-Co cemented carbides with similar grain sizes and binder contents and superior to conventionally prepared WC-Ni cemented carbides. In particular, the 2 vol% Ni composition had excellent hardness at room temperature of up to 2210HV10, while still having an indentation fracture toughness of 7 MPa.m(0.5). Therefore, WC-Ni cemented carbides processed by this novel approach are a promising alternative to conventional WC-Co cemented carbides for a wide range of applications.

This study presents a novel approach for the synthesis of WC-Ni cemented carbides with enhanced mechanical properties. A low-cost solution-based route was used to coat WC powders with well-distributed metallic nickel dots measuring between 17 nm and 39 nm in diameter. Varying compositions with loadings of 2, 6, and 14 vol% Ni were consolidated using spark plasma sintering (SPS) at 1350 degrees C under 50 MPa of uniaxial pressure giving relative densities of 99 +/- 1 %. The sintered WC-Ni cemented carbides had an even distribution of the Ni binder phase in all compositions, with retained ultrafine WC grain sizes of 0.5 +/- 0.1 mu m from the starting powder. The enhanced sinterability of the coated powders allowed for consolidation to near theoretical densities, with a binder content as low as 2 vol%. This is attributed to the uniform distribution of nickel and an extensive Ni-WC interface existing prior to sintering. The small size of the Ni dots likely also contributed to the solid-state sintering starting temperatures of as low as 800 degrees C. The mechanical performance of the resulting cemented carbides was evaluated by measuring the hardness at temperatures between 20 degrees C and 700 degrees C and estimating toughness at room temperature using Vickers indentations. These results showed that the mechanical properties of the WC-Ni cemented carbides synthesised by our method were comparable to conventionally prepared WC-Co cemented carbides with similar grain sizes and binder contents and superior to conventionally prepared WC-Ni cemented carbides. In particular, the 2 vol% Ni composition had excellent hardness at room temperature of up to 2210HV10, while still having an indentation fracture toughness of 7 MPa.m(0.5). Therefore, WC-Ni cemented carbides processed by this novel approach are a promising alternative to conventional WC-Co cemented carbides for a wide range of applications.

Two different grades, WC-20 vol.% Ni and WC-20 vol.% Co cemented carbides, respectively were systematically investigated concerning their microstructure, binder composition, and corrosion behavior. SEM-EBSD analysis verified that both grades have similar WC grain sizes (0.9-1.1 mu m). AES analysis confirmed that the binder phase of the respective grade is an alloy of Ni-W and Co-W and that the concentration of W in the Ni-and Co-binder is 21 and 10 at. %, respectively. In synthetic mine water (SMW), the EIS behavior of WC-Ni(W) at the open circuit potential (OCP) conditions was studied for different exposure periods (up to 120 h). The EIS data fitting estimates low capacitance and high charge transfer resistance (Rct) values, which indicate that the passive film formed on WC-Ni(W) is thin and exhibits high corrosion resistance. At the OCP and potentiostatic-passive conditions, SEM investigations confirm the uncorroded microstructure of the WC-Ni(W). The AR-XPS studies confirmed the formation of an extremely thin (0.25 nm) WO3 passive film is responsible for the high corrosion resistance of WC-Ni(W), at OCP conditions. However, above the transpassive potential, the microstructure instability of WC-Ni(W) was observed, i.e., corroded morphology of both WC grains and Ni(W) binder. The electrochemical parameters, Rct, corrosion current density, and charge density values, confirmed that the WC-Ni(W) is a far better alternative than the WC-Co(W) for application in SMW.

Two different grades, WC-20 vol.% Ni and WC-20 vol.% Co cemented carbides, respectively were systematically investigated concerning their microstructure, binder composition, and corrosion behavior. SEM-EBSD analysis verified that both grades have similar WC grain sizes (0.9-1.1 mu m). AES analysis confirmed that the binder phase of the respective grade is an alloy of Ni-W and Co-W and that the concentration of W in the Ni-and Co-binder is 21 and 10 at. %, respectively. In synthetic mine water (SMW), the EIS behavior of WC-Ni(W) at the open circuit potential (OCP) conditions was studied for different exposure periods (up to 120 h). The EIS data fitting estimates low capacitance and high charge transfer resistance (Rct) values, which indicate that the passive film formed on WC-Ni(W) is thin and exhibits high corrosion resistance. At the OCP and potentiostatic-passive conditions, SEM investigations confirm the uncorroded microstructure of the WC-Ni(W). The AR-XPS studies confirmed the formation of an extremely thin (0.25 nm) WO3 passive film is responsible for the high corrosion resistance of WC-Ni(W), at OCP conditions. However, above the transpassive potential, the microstructure instability of WC-Ni(W) was observed, i.e., corroded morphology of both WC grains and Ni(W) binder. The electrochemical parameters, Rct, corrosion current density, and charge density values, confirmed that the WC-Ni(W) is a far better alternative than the WC-Co(W) for application in SMW.

Two different grades, WC-20 vol.% Ni and WC-20 vol.% Co cemented carbides, respectively were systematically investigated concerning their microstructure, binder composition, and corrosion behavior. SEM-EBSD analysis verified that both grades have similar WC grain sizes (0.9-1.1 mu m). AES analysis confirmed that the binder phase of the respective grade is an alloy of Ni-W and Co-W and that the concentration of W in the Ni-and Co-binder is 21 and 10 at. %, respectively. In synthetic mine water (SMW), the EIS behavior of WC-Ni(W) at the open circuit potential (OCP) conditions was studied for different exposure periods (up to 120 h). The EIS data fitting estimates low capacitance and high charge transfer resistance (Rct) values, which indicate that the passive film formed on WC-Ni(W) is thin and exhibits high corrosion resistance. At the OCP and potentiostatic-passive conditions, SEM investigations confirm the uncorroded microstructure of the WC-Ni(W). The AR-XPS studies confirmed the formation of an extremely thin (0.25 nm) WO3 passive film is responsible for the high corrosion resistance of WC-Ni(W), at OCP conditions. However, above the transpassive potential, the microstructure instability of WC-Ni(W) was observed, i.e., corroded morphology of both WC grains and Ni(W) binder. The electrochemical parameters, Rct, corrosion current density, and charge density values, confirmed that the WC-Ni(W) is a far better alternative than the WC-Co(W) for application in SMW.

Integrated Computational Materials Engineering (ICME) has proved to be an efficient tool for understand-ing the process-structure-property relationships and helping us to design materials. For instance, in cemented carbides manufacturing, one of the most critical parameters is the C-window. It is defined as the C content range for which phases detrimental to the mechanical properties are avoided. This pro-cessing window has been traditionally defined using applied thermodynamics methods. However, the deviation between equilibrium calculations and real manufacturing conditions requires big additional empirical efforts to precisely define the C-window. In this work, an ICME-based approach is proposed to redefine the processability limits of cemented carbides taking the cooling rate and the material's initial powder size into consideration. The method relies on the interactive coupling of several adapted models and tools, to not only set the processability boundaries, but also to study the complex mechanisms inter-play happening along microstructural evolution. A better understanding of these underlaying mecha-nisms leads to new inputs that can be used in the design of cemented carbides. In this regard, it is observed that faster cooling rates or coarser WC grades could be effectively used to prevent nucleation of the detrimental phases enlarging the C-window towards lower C contents., QC 20230621

Liquid phase migration (LPM) and its potential impact on the phenomenon known as cobalt capping in cemented carbides have been investigated through experiments on fully densified, pre-sintered samples and simulations. A model for LPM was developed based on interface energies, grain size, and contiguity, and was implemented and integrated with Thermo-Calc software to make predictions about the final microstructure. The model's predictions, when applied to cases with gradients in grain size and volume fraction of the binder phase, were found to somewhat match experimental observations. Additionally, it was obsereved that LPM can cause a phenomenon resembling cobalt capping due to gradients in carbon activity., QC 20230316

Two different grades, WC-20 vol.% Ni and WC-20 vol.% Co cemented carbides, respectively were systematically investigated concerning their microstructure, binder composition, and corrosion behavior. SEM-EBSD analysis verified that both grades have similar WC grain sizes (0.9-1.1 mu m). AES analysis confirmed that the binder phase of the respective grade is an alloy of Ni-W and Co-W and that the concentration of W in the Ni-and Co-binder is 21 and 10 at. %, respectively. In synthetic mine water (SMW), the EIS behavior of WC-Ni(W) at the open circuit potential (OCP) conditions was studied for different exposure periods (up to 120 h). The EIS data fitting estimates low capacitance and high charge transfer resistance (Rct) values, which indicate that the passive film formed on WC-Ni(W) is thin and exhibits high corrosion resistance. At the OCP and potentiostatic-passive conditions, SEM investigations confirm the uncorroded microstructure of the WC-Ni(W). The AR-XPS studies confirmed the formation of an extremely thin (0.25 nm) WO3 passive film is responsible for the high corrosion resistance of WC-Ni(W), at OCP conditions. However, above the transpassive potential, the microstructure instability of WC-Ni(W) was observed, i.e., corroded morphology of both WC grains and Ni(W) binder. The electrochemical parameters, Rct, corrosion current density, and charge density values, confirmed that the WC-Ni(W) is a far better alternative than the WC-Co(W) for application in SMW.

This study presents a novel approach for the synthesis of WC-Ni cemented carbides with enhanced mechanical properties. A low-cost solution-based route was used to coat WC powders with well-distributed metallic nickel dots measuring between 17 nm and 39 nm in diameter. Varying compositions with loadings of 2, 6, and 14 vol% Ni were consolidated using spark plasma sintering (SPS) at 1350 degrees C under 50 MPa of uniaxial pressure giving relative densities of 99 +/- 1 %. The sintered WC-Ni cemented carbides had an even distribution of the Ni binder phase in all compositions, with retained ultrafine WC grain sizes of 0.5 +/- 0.1 mu m from the starting powder. The enhanced sinterability of the coated powders allowed for consolidation to near theoretical densities, with a binder content as low as 2 vol%. This is attributed to the uniform distribution of nickel and an extensive Ni-WC interface existing prior to sintering. The small size of the Ni dots likely also contributed to the solid-state sintering starting temperatures of as low as 800 degrees C. The mechanical performance of the resulting cemented carbides was evaluated by measuring the hardness at temperatures between 20 degrees C and 700 degrees C and estimating toughness at room temperature using Vickers indentations. These results showed that the mechanical properties of the WC-Ni cemented carbides synthesised by our method were comparable to conventionally prepared WC-Co cemented carbides with similar grain sizes and binder contents and superior to conventionally prepared WC-Ni cemented carbides. In particular, the 2 vol% Ni composition had excellent hardness at room temperature of up to 2210HV10, while still having an indentation fracture toughness of 7 MPa.m(0.5). Therefore, WC-Ni cemented carbides processed by this novel approach are a promising alternative to conventional WC-Co cemented carbides for a wide range of applications.

This study presents a novel approach for the synthesis of WC-Ni cemented carbides with enhanced mechanical properties. A low-cost solution-based route was used to coat WC powders with well-distributed metallic nickel dots measuring between 17 nm and 39 nm in diameter. Varying compositions with loadings of 2, 6, and 14 vol% Ni were consolidated using spark plasma sintering (SPS) at 1350 degrees C under 50 MPa of uniaxial pressure giving relative densities of 99 +/- 1 %. The sintered WC-Ni cemented carbides had an even distribution of the Ni binder phase in all compositions, with retained ultrafine WC grain sizes of 0.5 +/- 0.1 mu m from the starting powder. The enhanced sinterability of the coated powders allowed for consolidation to near theoretical densities, with a binder content as low as 2 vol%. This is attributed to the uniform distribution of nickel and an extensive Ni-WC interface existing prior to sintering. The small size of the Ni dots likely also contributed to the solid-state sintering starting temperatures of as low as 800 degrees C. The mechanical performance of the resulting cemented carbides was evaluated by measuring the hardness at temperatures between 20 degrees C and 700 degrees C and estimating toughness at room temperature using Vickers indentations. These results showed that the mechanical properties of the WC-Ni cemented carbides synthesised by our method were comparable to conventionally prepared WC-Co cemented carbides with similar grain sizes and binder contents and superior to conventionally prepared WC-Ni cemented carbides. In particular, the 2 vol% Ni composition had excellent hardness at room temperature of up to 2210HV10, while still having an indentation fracture toughness of 7 MPa.m(0.5). Therefore, WC-Ni cemented carbides processed by this novel approach are a promising alternative to conventional WC-Co cemented carbides for a wide range of applications.

A new concept for cemented carbide tools was presented with laser-generated abrasive-like protrusions on their machining surfaces that mimic the surface features of diamond or cubic boron nitride abrasives commonly used on honing tools. In this study, the surface structure on the new tools were protected by three different PVD ceramic hard coatings. All three nitride-based coatings, i.e., TiSiN-AlTiN, TiSiN-AlTiN-CrN and AlTiN-CrN, differed in the adhesion layer and coating structure. The coating-substrate systems were assessed by means of indenting and sliding contact testing in order to find out an appropriate one for the textured tools. Experimental methodology included (1) ‘passive’ Vickers indentation hardness tests, and (2) ‘active’ machining tests. In both cases, the resulting surface integrity was inspected by using FIB/SEM/EDS. It is found that both laser texturing and coating deposition changed the hardness. The tool coated by the two-layer film (TiSiN-AlTiN) achieved the best performance, in terms of both hardness enhancement and damage prevention experienced under both tests. Meanwhile, improvement was much less pronounced by the two-layer (AlTiN-CrN) coated tool. Here, cracks appeared under the Vickers indentations and the film was completely or partially spalled-off at some protrusion tops (cutting fronts), due to the concentrated stress during the machining. Finally, the three-layer coating with the TiSiN on the top (TiSiN-AlTiN-CrN) exhibited an intermediate response, where moderate hardness increase was combined with some wear – although less severe than for AlTiN-CrN film - taking place at critical points, such as cutting fronts, The work leading to this publication was supported by the Feodor Lynen Research Fellowship of the Alexander von Humboldt Foundation and by the individual research grant of the German Research Foundation (DFG-425923019). The authors acknowledge funding for the FIB/SEM instrument by the German Research Foundation (INST 256/510-1 FUGG). The authors express their gratitude to Photonik-Zentrum e.V., Kaiserslautern for supplying laser equipment support, to Saar- Hartmetall und Werkzeuge GmbH for supplying the studied materials, Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura, Objectius de Desenvolupament Sostenible::12 - Producció i Consum Responsables, Postprint (author's final draft)

Two different grades, WC-20 vol.% Ni and WC-20 vol.% Co cemented carbides, respectively were systematically investigated concerning their microstructure, binder composition, and corrosion behavior. SEM-EBSD analysis verified that both grades have similar WC grain sizes (0.9-1.1 mu m). AES analysis confirmed that the binder phase of the respective grade is an alloy of Ni-W and Co-W and that the concentration of W in the Ni-and Co-binder is 21 and 10 at. %, respectively. In synthetic mine water (SMW), the EIS behavior of WC-Ni(W) at the open circuit potential (OCP) conditions was studied for different exposure periods (up to 120 h). The EIS data fitting estimates low capacitance and high charge transfer resistance (Rct) values, which indicate that the passive film formed on WC-Ni(W) is thin and exhibits high corrosion resistance. At the OCP and potentiostatic-passive conditions, SEM investigations confirm the uncorroded microstructure of the WC-Ni(W). The AR-XPS studies confirmed the formation of an extremely thin (0.25 nm) WO3 passive film is responsible for the high corrosion resistance of WC-Ni(W), at OCP conditions. However, above the transpassive potential, the microstructure instability of WC-Ni(W) was observed, i.e., corroded morphology of both WC grains and Ni(W) binder. The electrochemical parameters, Rct, corrosion current density, and charge density values, confirmed that the WC-Ni(W) is a far better alternative than the WC-Co(W) for application in SMW.

In the constant pursuit of better-performing cemented carbides, recent studies suggest that a combination of better hardness and toughness can be obtained by changing its WC grain size distribution. As the area is still rather unexplored, this thesis aims to broaden the knowledge and answer whether mechanical properties can be changed by changing the WC grain size distribution, in the context of mining drill bit inserts. This was performed by producing four dual grained material as well as four single grained reference materials, for which the carbon content and presence of alloying element were varied. The materials were characterised and compared with regard to magnetic saturation, magnetic coercivity, hardness, fracture toughness, wear resistance, energy needed to cause fracture, as well as detailed microstructural analysis obtained through imaging and electron backscatter diffraction analysis The results showed that mining drill bit inserts with alternative WC grain size distribution could successfully be produced, but that a traditional bimodal distribution with two peaks could not be obtained. The distribution instead became significantly wider as well as skewed towards larger grains for the dual grained materials compared with their references. It was further also confirmed that the alternative dual grain size distribution could be used to improve the mechanical properties of fracture toughness and wear resistance, but only for material that was not alloyed, and the magnitude of the improvement may be considered to be small. For the alloyed materials, it turned out to be more difficult to influence the mechanical properties, as the improving effect of analloying element outweighed the effect of grain size distribution., I en ständig jakt på hårdmetall med bättre prestanda, så föreslår ny forskning att en bättre kombination av hårdhet och seghet kan erhållas genom att ändra den mikrostrukturiella WC-kornstorleksfördelning. Då det ännu är ett relativt outforskat område, så har denna studie för avsikt att öka kunskapen genom att besvara frågan om de mekaniska egenskaperna kan förändras genom att ändra på materialets kornstorleksfördelning inom applikationsområdet hårdmetall för bergborrning. Detta gjordes genom att producera fyra material med WC pulver av två olika storlekar, samt fyra referensmaterial med en kornstorlek. För dessa varierades parametrarna kolhalt och närvaro av legeringselement. Materialen karakteriserades och jämfördes med avseende på magnetisk mättnad, magnetisk koercivitet, hårdhet, brottseghet, slitstyrka, energi som behövs för att orsaka brott, samt en detaljerad mikrostrukturanalys som erhölls genom avbildning samt elektrondiffraktionsanalys. Resultaten visade att material med alternativ WC-kornstorleksfördelning kunde produceras, men att en fullt bimodal fördelning inte gick att skapa i denna studie. Fördelningen blev istället betydligt bredare samt förskjuten mot större korn för materialen som innhöll WC av två olika storlekar. Det bekräftades också att den alternativa kornstorleksfördelningen kunde förbättra de mekaniska egenskaperna för brottseghet och slitstyrka, men endast för de material som inte var legerade och storleken på förbättringen får dessutom anses vara relativt liten. För de legerade materialen visade det sig vara svårare att påverka de mekaniska egenskaperna, eftersom den förbättring av egenskaper som legeringselement tillförde överträffade effekten av kornstorleksfördelning.

Cemented carbides, or hard metals, are ceramic–metal composites usually consisting of tungsten carbide particles bound by a cobalt-based alloy. They are the backbone materials for the tooling industry, as a direct consequence of the outstanding range of property combinations, depending on their effective microstructural assemblage, i.e., the physical dimensions and relative content of their constitutive phases. Hence, reliable microstructural characterization becomes key for hard metal grade selection and quality control. This work aimed to assess the practical twodimensional characterization methods for the most important one- and two-phase properties of cemented carbides, i.e., the carbide grain size, phase fraction, carbide contiguity, and binder mean free path. Three different methods—point, line, and area analysis—were implemented to characterize four microstructurally distinct grades. The images were acquired by optical and scanning electron microscopy, with the latter through both secondary and backscattered electrons. Results were critically discussed by comparing the obtained values of properties and the different characterization methodology. Inspection technique combinations were finally ranked based on accuracy, accessibility, and operability considerations. The line method was used to analyze all the properties, the area method, for the one-phase properties, and the point method, for only the phase fraction. It was found that the combination of optical microscopy and the line analysis method was suitable for a direct inspection and rapid estimation for carbides above fine grain size. The most precise results were achieved using line analysis of the images obtained by the backscattered electrons of the scanning electron microscope, The work leading to this publication was supported by the Feodor Lynen Research Fellowship of the Alexander von Humboldt Foundation, by the individual research grant from the Deutsche Forschungsgemeinschaft (DFG-425923019), by the Spanish Ministerio de Ciencia e Innovación MICINN-FEDER (Spain) through grant PID2019-106631GB-C41 (AEI/10.13039/501100011033), and by the “Open Access Publication Funding” program of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) and Saarland University. The work also obtained funding for the FIB/SEM instrument used for SEM imaging and EBSD by the Deutsche Forschungsgemeinschaft (INST 256/510-1 FUGG), Postprint (published version)

The effect of corrosion-induced changes on the contact fatigue response and associated damage in a medium-grained WC-6%wtCo hardmetal grade is investigated. Cyclic contact loading tests are conducted by means of Hertzian indentation techniques. Corrosion damage is introduced in a controlled way by previous immersion of specimens in a stirred acidic medium. Results reveal that corrosion significantly affects the contact fatigue behavior of the material under consideration, in terms of decreasing the effective load bearing capability of the material as well as earlier emergence and evolution of specific damage features, as compared to those discerned under monotonic loading and in a pristine hardmetal respectively. As cycle number increases, damage evolution in the corroded condition is more gradual and diffuse than for the uncorroded one. In general, it is dominated by existence of ill-defined radial cracks together with pronounced carbide grain pull-out which finally evolve into cohesive-like spallation in regions close to the periphery of indentation imprints. These findings are rationalized on the basis of phase assemblage changes linked to corrosion, particularly in terms of lessening of toughening capability and easiness of WC grain pull-out intrinsic to the loose and porous binderless WC skeleton remnant at the surface level, after exposure to the acid medium. Although some removal of carbide grains and discrete cohesive chipping is also observed in the pristine sample for very high number of cycles, such different response, as compared to monotonic loading, is linked to oxidation phenomena of the metallic binder for this reference condition., Peer Reviewed, Postprint (author's final draft)

In the constant pursuit of better-performing cemented carbides, recent studies suggest that a combination of better hardness and toughness can be obtained by changing its WC grain size distribution. As the area is still rather unexplored, this thesis aims to broaden the knowledge and answer whether mechanical properties can be changed by changing the WC grain size distribution, in the context of mining drill bit inserts. This was performed by producing four dual grained material as well as four single grained reference materials, for which the carbon content and presence of alloying element were varied. The materials were characterised and compared with regard to magnetic saturation, magnetic coercivity, hardness, fracture toughness, wear resistance, energy needed to cause fracture, as well as detailed microstructural analysis obtained through imaging and electron backscatter diffraction analysis The results showed that mining drill bit inserts with alternative WC grain size distribution could successfully be produced, but that a traditional bimodal distribution with two peaks could not be obtained. The distribution instead became significantly wider as well as skewed towards larger grains for the dual grained materials compared with their references. It was further also confirmed that the alternative dual grain size distribution could be used to improve the mechanical properties of fracture toughness and wear resistance, but only for material that was not alloyed, and the magnitude of the improvement may be considered to be small. For the alloyed materials, it turned out to be more difficult to influence the mechanical properties, as the improving effect of analloying element outweighed the effect of grain size distribution., I en ständig jakt på hårdmetall med bättre prestanda, så föreslår ny forskning att en bättre kombination av hårdhet och seghet kan erhållas genom att ändra den mikrostrukturiella WC-kornstorleksfördelning. Då det ännu är ett relativt outforskat område, så har denna studie för avsikt att öka kunskapen genom att besvara frågan om de mekaniska egenskaperna kan förändras genom att ändra på materialets kornstorleksfördelning inom applikationsområdet hårdmetall för bergborrning. Detta gjordes genom att producera fyra material med WC pulver av två olika storlekar, samt fyra referensmaterial med en kornstorlek. För dessa varierades parametrarna kolhalt och närvaro av legeringselement. Materialen karakteriserades och jämfördes med avseende på magnetisk mättnad, magnetisk koercivitet, hårdhet, brottseghet, slitstyrka, energi som behövs för att orsaka brott, samt en detaljerad mikrostrukturanalys som erhölls genom avbildning samt elektrondiffraktionsanalys. Resultaten visade att material med alternativ WC-kornstorleksfördelning kunde produceras, men att en fullt bimodal fördelning inte gick att skapa i denna studie. Fördelningen blev istället betydligt bredare samt förskjuten mot större korn för materialen som innhöll WC av två olika storlekar. Det bekräftades också att den alternativa kornstorleksfördelningen kunde förbättra de mekaniska egenskaperna för brottseghet och slitstyrka, men endast för de material som inte var legerade och storleken på förbättringen får dessutom anses vara relativt liten. För de legerade materialen visade det sig vara svårare att påverka de mekaniska egenskaperna, eftersom den förbättring av egenskaper som legeringselement tillförde överträffade effekten av kornstorleksfördelning.

Tungsten carbide based cemented carbides, often simply termed hardmetals, are established forefront materials for tools, structural components, and wear parts with stringent requirements. Several of the technological applications in which they are used include exposure to chemically aggressive media. Under these conditions, failure induced under applied load may be accelerated; and consequently, the service life may be decreased. Within this context, this work addresses the influence of corrosion-induced damage on the mechanical integrity and load-bearing capability of hardmetals at different length scales, i.e., from 100s nanometers to 1000s microns. Experimental data acquired by means of nanoindentation, pyramidal, and spherical indentation, as well as sliding contact (micro- and nanoscratch) techniques, are presented. The attained results allow for identifying guidelines for the microstructural design of these materials under combined consideration of corrosion and mechanical contact as service-like conditions. Discussion of the reported findings includes a critical analysis of corrosion effects on the evolution of microstructure-property-performance interrelations for the materials under consideration., Peer Reviewed, Postprint (published version)

The use of fracture mechanics for rationalizing the fracture behavior of cemented carbides is valid, as far as sharp cracks, free of residual stresses and subjected to a well-defined stress state are used for assessing fracture toughness. However, machining a very sharp notch on the surface of hardmetals for fracture toughness testing has been a critical issue during many years. Within this context, introduction of surface “through-thickness” micronotches (SEµVNB) by means of ultrashort pulsed laser ablation (UPLA) is here proposed, implemented and analyzed as an innovative precracking-like route within flexural testing procedures for appropiated evaluation of fracture toughness of cemented carbides. UPLA parameters used for introducing the micronotch are optimized in terms of induced damage ahead of the notch tip. For comparison purposes, fracture toughness is also determined by means of flexural testing of previously cracked single-edge notch beams (SENB-Cracked) as well as specimens with V-notch tips sharpened through diamond polishing using a razor blade, and Palmqvist indentation microfracture method. The satisfactory agreement found between values measured using UPLA-micronotched and SENB-Cracked (reference) specimens allows to conclude that flexural testing of SEµVNB samples is a valid methodology for reliable determination of fracture toughness of hardmetals. This is feasible because of the extremely short time of laser-matter interaction. It yields small and somehow controlled damage in front of the notch tip as a result of shock wave propagation during ablation, which translates into effective precracking of SEµVNB specimens. Previous article in issue, Peer Reviewed, Postprint (author's final draft)

Since their discovery about 100 years ago, tools made of hard metals have been the enablers of development in various areas: from drilling subway lines for more sustainable cities to the machining of complex next-generation airplane engine parts for reduced CO2 emissions. An increase in properties of hard metals thus leads to efficient operations with shorter lead-time, less environmental footprint, and reduced cost. To tailor the as-sintered hard metal structure with desired properties and develop reliable modelling tools, it is critical to have statistically representative experimental data acquired in conditions mimicking the real processes for hard metals. However, to date, nano- and microstructural investigations of hard metals and related systems have been mainly focused on the lab-scale techniques, limiting the bulk-scale in-situ investigations. This thesis focuses on neutron scattering techniques and demonstrates how the utilization of small angle neutron scattering (SANS) techniques and neutron diffraction (ND) in a complementary manner with lab-scale techniques and computational tools can enhance the mechanistic understanding during processing of hard metals and related systems. Some of the presented information within the thesis is unique to neutron scattering experiments. SANS experiments are used for the quantification of nano- and microstructural features including Co-rich binder pocket size, WC grain size, and size and volume fraction of (V,W)Cx interfacial layers. The quantitative data enables us to draw conclusions regarding the mechanism of grain coarsening inhibition in V-doped hard metals at different V additions. The findings indicate that the grain coarsening inhibition in V-doped hard metals originates from reduced WC/Co interface mobility and total driving force for coarsening. The complex nature of structural evolution at sintering temperatures is further investigated by in-situ SANS up to 1500 oC. Our results show that the size and volume, Sedan upptäckten av hårdmetall för cirka 100 år sedan har verktyg gjorda av hårdmetall varit avgörande för tillämpningar inom olika områden såsom borrning av tunnelbanelinjer för mer hållbara städer och bearbetning av nästa generations flygplansmotorer för minskade CO2-utsläpp. Förbättrade egenskaper hos hårdmetallen leder således till ökad effektivitet i olika verktygsoperationer med kortare ledtid, mindre miljöpåverkan och minskade kostnader för till exempel tillverkning. För att skräddarsy den sintrade hårdmetallstrukturen och skapa önskade egenskaper är det viktigt att ha statistiskt representativ experimentell data som uppmätts under förhållanden som efterliknar de verkliga processerna inom industrin. Hittills har dock nano- och mikrostrukturundersökningar av hårdmetaller och relaterade system huvudsakligen varit begränsade till laboratorietekniker, vilket begränsat in-situ-undersökningar av materialens bulk. Den här avhandlingen använder neutronspridningstekniker på olika relevanta hårdmetallsystem och visar på hur lågvinkelspridning (SANS) och neutrondiffraktion (ND) kan komplettera konventionella laboratorietekniker och beräkningsverktyg för att förbättra förståelsen av meknismer som styr materialets utveckling under olika processer. En del av datat som presenteras i avhandlingen kan endast uppnås med hjälp av neutronspridningsexperiment. SANS-experiment används för kvantifiering av nano- och mikrostrukturella egenskaper inklusive mätning av den Co-rika bindefasens storlek, kornstorlek hos WC och storleken och volymsfraktionen av (V,W)Cx-gränsskikt. Den kvantitativa datan gör det möjligt för oss att dra slutsatser angående mekanismen för inhibering av kornförgrovning i V-dopade hårdmetaller vid olika V-tillsatser. Resultaten tyder på att kornförgrovningsinhiberingen i V-dopade hårdmetaller härrör från minskad rörlighet av WC/Co-gränskikt och minskad total drivkraft för förgrovning. Den komplexa karaktären av den strukturell utveckling vid sintringstemperat, Stiftelsen för Strategisk Forskning (SSF): SwedNESS - Sveriges neutronforskarskola (GSn15-0008)

The correlation between granule strength and green strength of hard metal powders is examined. The approach is based on experiments and numerics. In the latter case, a Design of Experiment software is used. The granule strength of the powder (particle) is determined by GFP-measurements (“Granularfestigkeits-Prüfsystem”). During this test, a single particle is pressed from one side until breakage. The corresponding measurements of the green strength are done using three-point bend (3PB) testing. The experimental results show that the pressing agent has a strong influence on the behavior of both quantities. The statistical evaluation shows that the relation between the two strength properties is very close to linear with coefficient of determination R2 taking on the value 0.97. This of course indicates that it is possible to get information about one of the properties for a similar set of materials by experimentally determining the other one. This is of substantial practical importance as for one thing it can limit the amount of testing required. Even though the present investigation is pertinent to hard metal powders, the results could be of value for many other types of powder materials., QC 20220427

Since their discovery about 100 years ago, tools made of hard metals have been the enablers of development in various areas: from drilling subway lines for more sustainable cities to the machining of complex next-generation airplane engine parts for reduced CO2 emissions. An increase in properties of hard metals thus leads to efficient operations with shorter lead-time, less environmental footprint, and reduced cost. To tailor the as-sintered hard metal structure with desired properties and develop reliable modelling tools, it is critical to have statistically representative experimental data acquired in conditions mimicking the real processes for hard metals. However, to date, nano- and microstructural investigations of hard metals and related systems have been mainly focused on the lab-scale techniques, limiting the bulk-scale in-situ investigations. This thesis focuses on neutron scattering techniques and demonstrates how the utilization of small angle neutron scattering (SANS) techniques and neutron diffraction (ND) in a complementary manner with lab-scale techniques and computational tools can enhance the mechanistic understanding during processing of hard metals and related systems. Some of the presented information within the thesis is unique to neutron scattering experiments. SANS experiments are used for the quantification of nano- and microstructural features including Co-rich binder pocket size, WC grain size, and size and volume fraction of (V,W)Cx interfacial layers. The quantitative data enables us to draw conclusions regarding the mechanism of grain coarsening inhibition in V-doped hard metals at different V additions. The findings indicate that the grain coarsening inhibition in V-doped hard metals originates from reduced WC/Co interface mobility and total driving force for coarsening. The complex nature of structural evolution at sintering temperatures is further investigated by in-situ SANS up to 1500 oC. Our results show that the size and volume, Sedan upptäckten av hårdmetall för cirka 100 år sedan har verktyg gjorda av hårdmetall varit avgörande för tillämpningar inom olika områden såsom borrning av tunnelbanelinjer för mer hållbara städer och bearbetning av nästa generations flygplansmotorer för minskade CO2-utsläpp. Förbättrade egenskaper hos hårdmetallen leder således till ökad effektivitet i olika verktygsoperationer med kortare ledtid, mindre miljöpåverkan och minskade kostnader för till exempel tillverkning. För att skräddarsy den sintrade hårdmetallstrukturen och skapa önskade egenskaper är det viktigt att ha statistiskt representativ experimentell data som uppmätts under förhållanden som efterliknar de verkliga processerna inom industrin. Hittills har dock nano- och mikrostrukturundersökningar av hårdmetaller och relaterade system huvudsakligen varit begränsade till laboratorietekniker, vilket begränsat in-situ-undersökningar av materialens bulk. Den här avhandlingen använder neutronspridningstekniker på olika relevanta hårdmetallsystem och visar på hur lågvinkelspridning (SANS) och neutrondiffraktion (ND) kan komplettera konventionella laboratorietekniker och beräkningsverktyg för att förbättra förståelsen av meknismer som styr materialets utveckling under olika processer. En del av datat som presenteras i avhandlingen kan endast uppnås med hjälp av neutronspridningsexperiment. SANS-experiment används för kvantifiering av nano- och mikrostrukturella egenskaper inklusive mätning av den Co-rika bindefasens storlek, kornstorlek hos WC och storleken och volymsfraktionen av (V,W)Cx-gränsskikt. Den kvantitativa datan gör det möjligt för oss att dra slutsatser angående mekanismen för inhibering av kornförgrovning i V-dopade hårdmetaller vid olika V-tillsatser. Resultaten tyder på att kornförgrovningsinhiberingen i V-dopade hårdmetaller härrör från minskad rörlighet av WC/Co-gränskikt och minskad total drivkraft för förgrovning. Den komplexa karaktären av den strukturell utveckling vid sintringstemperat, Stiftelsen för Strategisk Forskning (SSF): SwedNESS - Sveriges neutronforskarskola (GSn15-0008)

As Ti-alloys become more and more utilized the need for efficient and robust manufacturing of Ti-alloy components increase in importance. Ti-alloys are more difficult to machine than e.g. steel, mainly due to their poor thermal conductivity leading to rapid tool wear. The atomic scale processes responsible for this wear is not well understood. Here the focus is turned to the effects of C diffusion out of the tools as a source of the observed wear. A combination of Density Functional Theory (DFT) making use of Harmonic Transition State Theory (HTST), classical Molecular Dynamics (MD) and kinetic Monte Carlo (kMC) is used to investigate C diffusion into and within experimentally observed WC/W interfaces that exists as a consequence of the C depletion. Further, tools are built and used to evaluate interface parameters for large sets of interfaces within the WC/W system to determine which are energetically preferred. The results from the DFT study show stable interfaces with large differences in activation energy between the two most prominent surfaces found in WC materials, namely the basal and prismatic surfaces. Within the WC/W interfaces the diffusion barriers are similar between the two. The classical MD simulations support the view of stable interfaces at the early stages of C depletion. As C is removed this picture shifts to one in which the diffusion barriers are substantially decreased and the difference between the basal and the prismatic interfaces vanish pointing to a process which starts out slow but accelerates as C is continually removed. From the kMC simulations the overall diffusion pre-factor and activation energy is estimated to be D0=1.8x10-8 m2/s and dE=1.24 eV for the investigated [10-10]-I/[100] interface, the kMC simulations also confirm previous results indicating that the diffusion is restricted to the interface region. The investigation and screening of properties for WC/W interfaces show a preference for the W terminated [10-10]-I/[110] and [

Drill bits equipped with WC-Co cemented carbide buttons offer great performance in many rock drilling applications. Generally, the wear of these buttons against the rock is gradual and moderate, or even slow depending on the rock conditions. However, the Co binder has recently been found to cause health issues and an alternative binder, which does not compromise the performance of the cemented carbide, is needed. In the present work, the performance of WC-Fe and WC-Ni is investigated and compared to the common WC-Co in a sliding test against granite. The results show immediate scrape-off of granite against protruding WC grain edges. Some WC grains crack and fragments are subsequently removed, adding up to loss of entire WC grains. A nanoscale pattern gradually evolves on other WC grains, implying also nanoscale wear. Both WC-Fe and WC-Ni show significantly faster wear initiation and early propagation compared to WC-Co, although the wear characteristics are similar.

Drill bits equipped with WC-Co cemented carbide buttons offer great performance in many rock drilling applications. Generally, the wear of these buttons against the rock is gradual and moderate, or even slow depending on the rock conditions. However, the Co binder has recently been found to cause health issues and an alternative binder, which does not compromise the performance of the cemented carbide, is needed. In the present work, the performance of WC-Fe and WC-Ni is investigated and compared to the common WC-Co in a sliding test against granite. The results show immediate scrape-off of granite against protruding WC grain edges. Some WC grains crack and fragments are subsequently removed, adding up to loss of entire WC grains. A nanoscale pattern gradually evolves on other WC grains, implying also nanoscale wear. Both WC-Fe and WC-Ni show significantly faster wear initiation and early propagation compared to WC-Co, although the wear characteristics are similar.

Drill bits equipped with WC-Co cemented carbide buttons offer great performance in many rock drilling applications. Generally, the wear of these buttons against the rock is gradual and moderate, or even slow depending on the rock conditions. However, the Co binder has recently been found to cause health issues and an alternative binder, which does not compromise the performance of the cemented carbide, is needed. In the present work, the performance of WC-Fe and WC-Ni is investigated and compared to the common WC-Co in a sliding test against granite. The results show immediate scrape-off of granite against protruding WC grain edges. Some WC grains crack and fragments are subsequently removed, adding up to loss of entire WC grains. A nanoscale pattern gradually evolves on other WC grains, implying also nanoscale wear. Both WC-Fe and WC-Ni show significantly faster wear initiation and early propagation compared to WC-Co, although the wear characteristics are similar.

As Ti-alloys become more and more utilized the need for efficient and robust manufacturing of Ti-alloy components increase in importance. Ti-alloys are more difficult to machine than e.g. steel, mainly due to their poor thermal conductivity leading to rapid tool wear. The atomic scale processes responsible for this wear is not well understood. Here the focus is turned to the effects of C diffusion out of the tools as a source of the observed wear. A combination of Density Functional Theory (DFT) making use of Harmonic Transition State Theory (HTST), classical Molecular Dynamics (MD) and kinetic Monte Carlo (kMC) is used to investigate C diffusion into and within experimentally observed WC/W interfaces that exists as a consequence of the C depletion. Further, tools are built and used to evaluate interface parameters for large sets of interfaces within the WC/W system to determine which are energetically preferred. The results from the DFT study show stable interfaces with large differences in activation energy between the two most prominent surfaces found in WC materials, namely the basal and prismatic surfaces. Within the WC/W interfaces the diffusion barriers are similar between the two. The classical MD simulations support the view of stable interfaces at the early stages of C depletion. As C is removed this picture shifts to one in which the diffusion barriers are substantially decreased and the difference between the basal and the prismatic interfaces vanish pointing to a process which starts out slow but accelerates as C is continually removed. From the kMC simulations the overall diffusion pre-factor and activation energy is estimated to be D0=1.8x10-8 m2/s and dE=1.24 eV for the investigated [10-10]-I/[100] interface, the kMC simulations also confirm previous results indicating that the diffusion is restricted to the interface region. The investigation and screening of properties for WC/W interfaces show a preference for the W terminated [10-10]-I/[110] and [

Drill bits equipped with WC-Co cemented carbide buttons offer great performance in many rock drilling applications. Generally, the wear of these buttons against the rock is gradual and moderate, or even slow depending on the rock conditions. However, the Co binder has recently been found to cause health issues and an alternative binder, which does not compromise the performance of the cemented carbide, is needed. In the present work, the performance of WC-Fe and WC-Ni is investigated and compared to the common WC-Co in a sliding test against granite. The results show immediate scrape-off of granite against protruding WC grain edges. Some WC grains crack and fragments are subsequently removed, adding up to loss of entire WC grains. A nanoscale pattern gradually evolves on other WC grains, implying also nanoscale wear. Both WC-Fe and WC-Ni show significantly faster wear initiation and early propagation compared to WC-Co, although the wear characteristics are similar.

As Ti-alloys become more and more utilized the need for efficient and robust manufacturing of Ti-alloy components increase in importance. Ti-alloys are more difficult to machine than e.g. steel, mainly due to their poor thermal conductivity leading to rapid tool wear. The atomic scale processes responsible for this wear is not well understood. Here the focus is turned to the effects of C diffusion out of the tools as a source of the observed wear. A combination of Density Functional Theory (DFT) making use of Harmonic Transition State Theory (HTST), classical Molecular Dynamics (MD) and kinetic Monte Carlo (kMC) is used to investigate C diffusion into and within experimentally observed WC/W interfaces that exists as a consequence of the C depletion. Further, tools are built and used to evaluate interface parameters for large sets of interfaces within the WC/W system to determine which are energetically preferred. The results from the DFT study show stable interfaces with large differences in activation energy between the two most prominent surfaces found in WC materials, namely the basal and prismatic surfaces. Within the WC/W interfaces the diffusion barriers are similar between the two. The classical MD simulations support the view of stable interfaces at the early stages of C depletion. As C is removed this picture shifts to one in which the diffusion barriers are substantially decreased and the difference between the basal and the prismatic interfaces vanish pointing to a process which starts out slow but accelerates as C is continually removed. From the kMC simulations the overall diffusion pre-factor and activation energy is estimated to be D0=1.8x10-8 m2/s and dE=1.24 eV for the investigated [10-10]-I/[100] interface, the kMC simulations also confirm previous results indicating that the diffusion is restricted to the interface region. The investigation and screening of properties for WC/W interfaces show a preference for the W terminated [10-10]-I/[110] and [

Since their discovery about 100 years ago, tools made of hard metals have been the enablers of development in various areas: from drilling subway lines for more sustainable cities to the machining of complex next-generation airplane engine parts for reduced CO2 emissions. An increase in properties of hard metals thus leads to efficient operations with shorter lead-time, less environmental footprint, and reduced cost. To tailor the as-sintered hard metal structure with desired properties and develop reliable modelling tools, it is critical to have statistically representative experimental data acquired in conditions mimicking the real processes for hard metals. However, to date, nano- and microstructural investigations of hard metals and related systems have been mainly focused on the lab-scale techniques, limiting the bulk-scale in-situ investigations. This thesis focuses on neutron scattering techniques and demonstrates how the utilization of small angle neutron scattering (SANS) techniques and neutron diffraction (ND) in a complementary manner with lab-scale techniques and computational tools can enhance the mechanistic understanding during processing of hard metals and related systems. Some of the presented information within the thesis is unique to neutron scattering experiments. SANS experiments are used for the quantification of nano- and microstructural features including Co-rich binder pocket size, WC grain size, and size and volume fraction of (V,W)Cx interfacial layers. The quantitative data enables us to draw conclusions regarding the mechanism of grain coarsening inhibition in V-doped hard metals at different V additions. The findings indicate that the grain coarsening inhibition in V-doped hard metals originates from reduced WC/Co interface mobility and total driving force for coarsening. The complex nature of structural evolution at sintering temperatures is further investigated by in-situ SANS up to 1500 oC. Our results show that the size and volume, Sedan upptäckten av hårdmetall för cirka 100 år sedan har verktyg gjorda av hårdmetall varit avgörande för tillämpningar inom olika områden såsom borrning av tunnelbanelinjer för mer hållbara städer och bearbetning av nästa generations flygplansmotorer för minskade CO2-utsläpp. Förbättrade egenskaper hos hårdmetallen leder således till ökad effektivitet i olika verktygsoperationer med kortare ledtid, mindre miljöpåverkan och minskade kostnader för till exempel tillverkning. För att skräddarsy den sintrade hårdmetallstrukturen och skapa önskade egenskaper är det viktigt att ha statistiskt representativ experimentell data som uppmätts under förhållanden som efterliknar de verkliga processerna inom industrin. Hittills har dock nano- och mikrostrukturundersökningar av hårdmetaller och relaterade system huvudsakligen varit begränsade till laboratorietekniker, vilket begränsat in-situ-undersökningar av materialens bulk. Den här avhandlingen använder neutronspridningstekniker på olika relevanta hårdmetallsystem och visar på hur lågvinkelspridning (SANS) och neutrondiffraktion (ND) kan komplettera konventionella laboratorietekniker och beräkningsverktyg för att förbättra förståelsen av meknismer som styr materialets utveckling under olika processer. En del av datat som presenteras i avhandlingen kan endast uppnås med hjälp av neutronspridningsexperiment. SANS-experiment används för kvantifiering av nano- och mikrostrukturella egenskaper inklusive mätning av den Co-rika bindefasens storlek, kornstorlek hos WC och storleken och volymsfraktionen av (V,W)Cx-gränsskikt. Den kvantitativa datan gör det möjligt för oss att dra slutsatser angående mekanismen för inhibering av kornförgrovning i V-dopade hårdmetaller vid olika V-tillsatser. Resultaten tyder på att kornförgrovningsinhiberingen i V-dopade hårdmetaller härrör från minskad rörlighet av WC/Co-gränskikt och minskad total drivkraft för förgrovning. Den komplexa karaktären av den strukturell utveckling vid sintringstemperat, Stiftelsen för Strategisk Forskning (SSF): SwedNESS - Sveriges neutronforskarskola (GSn15-0008)

Since their discovery about 100 years ago, tools made of hard metals have been the enablers of development in various areas: from drilling subway lines for more sustainable cities to the machining of complex next-generation airplane engine parts for reduced CO2 emissions. An increase in properties of hard metals thus leads to efficient operations with shorter lead-time, less environmental footprint, and reduced cost. To tailor the as-sintered hard metal structure with desired properties and develop reliable modelling tools, it is critical to have statistically representative experimental data acquired in conditions mimicking the real processes for hard metals. However, to date, nano- and microstructural investigations of hard metals and related systems have been mainly focused on the lab-scale techniques, limiting the bulk-scale in-situ investigations. This thesis focuses on neutron scattering techniques and demonstrates how the utilization of small angle neutron scattering (SANS) techniques and neutron diffraction (ND) in a complementary manner with lab-scale techniques and computational tools can enhance the mechanistic understanding during processing of hard metals and related systems. Some of the presented information within the thesis is unique to neutron scattering experiments. SANS experiments are used for the quantification of nano- and microstructural features including Co-rich binder pocket size, WC grain size, and size and volume fraction of (V,W)Cx interfacial layers. The quantitative data enables us to draw conclusions regarding the mechanism of grain coarsening inhibition in V-doped hard metals at different V additions. The findings indicate that the grain coarsening inhibition in V-doped hard metals originates from reduced WC/Co interface mobility and total driving force for coarsening. The complex nature of structural evolution at sintering temperatures is further investigated by in-situ SANS up to 1500 oC. Our results show that the size and volume, Sedan upptäckten av hårdmetall för cirka 100 år sedan har verktyg gjorda av hårdmetall varit avgörande för tillämpningar inom olika områden såsom borrning av tunnelbanelinjer för mer hållbara städer och bearbetning av nästa generations flygplansmotorer för minskade CO2-utsläpp. Förbättrade egenskaper hos hårdmetallen leder således till ökad effektivitet i olika verktygsoperationer med kortare ledtid, mindre miljöpåverkan och minskade kostnader för till exempel tillverkning. För att skräddarsy den sintrade hårdmetallstrukturen och skapa önskade egenskaper är det viktigt att ha statistiskt representativ experimentell data som uppmätts under förhållanden som efterliknar de verkliga processerna inom industrin. Hittills har dock nano- och mikrostrukturundersökningar av hårdmetaller och relaterade system huvudsakligen varit begränsade till laboratorietekniker, vilket begränsat in-situ-undersökningar av materialens bulk. Den här avhandlingen använder neutronspridningstekniker på olika relevanta hårdmetallsystem och visar på hur lågvinkelspridning (SANS) och neutrondiffraktion (ND) kan komplettera konventionella laboratorietekniker och beräkningsverktyg för att förbättra förståelsen av meknismer som styr materialets utveckling under olika processer. En del av datat som presenteras i avhandlingen kan endast uppnås med hjälp av neutronspridningsexperiment. SANS-experiment används för kvantifiering av nano- och mikrostrukturella egenskaper inklusive mätning av den Co-rika bindefasens storlek, kornstorlek hos WC och storleken och volymsfraktionen av (V,W)Cx-gränsskikt. Den kvantitativa datan gör det möjligt för oss att dra slutsatser angående mekanismen för inhibering av kornförgrovning i V-dopade hårdmetaller vid olika V-tillsatser. Resultaten tyder på att kornförgrovningsinhiberingen i V-dopade hårdmetaller härrör från minskad rörlighet av WC/Co-gränskikt och minskad total drivkraft för förgrovning. Den komplexa karaktären av den strukturell utveckling vid sintringstemperat, Stiftelsen för Strategisk Forskning (SSF): SwedNESS - Sveriges neutronforskarskola (GSn15-0008)

As Ti-alloys become more and more utilized the need for efficient and robust manufacturing of Ti-alloy components increase in importance. Ti-alloys are more difficult to machine than e.g. steel, mainly due to their poor thermal conductivity leading to rapid tool wear. The atomic scale processes responsible for this wear is not well understood. Here the focus is turned to the effects of C diffusion out of the tools as a source of the observed wear. A combination of Density Functional Theory (DFT) making use of Harmonic Transition State Theory (HTST), classical Molecular Dynamics (MD) and kinetic Monte Carlo (kMC) is used to investigate C diffusion into and within experimentally observed WC/W interfaces that exists as a consequence of the C depletion. Further, tools are built and used to evaluate interface parameters for large sets of interfaces within the WC/W system to determine which are energetically preferred. The results from the DFT study show stable interfaces with large differences in activation energy between the two most prominent surfaces found in WC materials, namely the basal and prismatic surfaces. Within the WC/W interfaces the diffusion barriers are similar between the two. The classical MD simulations support the view of stable interfaces at the early stages of C depletion. As C is removed this picture shifts to one in which the diffusion barriers are substantially decreased and the difference between the basal and the prismatic interfaces vanish pointing to a process which starts out slow but accelerates as C is continually removed. From the kMC simulations the overall diffusion pre-factor and activation energy is estimated to be D0=1.8x10-8 m2/s and dE=1.24 eV for the investigated [10-10]-I/[100] interface, the kMC simulations also confirm previous results indicating that the diffusion is restricted to the interface region. The investigation and screening of properties for WC/W interfaces show a preference for the W terminated [10-10]-I/[110] and [

Since their discovery about 100 years ago, tools made of hard metals have been the enablers of development in various areas: from drilling subway lines for more sustainable cities to the machining of complex next-generation airplane engine parts for reduced CO2 emissions. An increase in properties of hard metals thus leads to efficient operations with shorter lead-time, less environmental footprint, and reduced cost. To tailor the as-sintered hard metal structure with desired properties and develop reliable modelling tools, it is critical to have statistically representative experimental data acquired in conditions mimicking the real processes for hard metals. However, to date, nano- and microstructural investigations of hard metals and related systems have been mainly focused on the lab-scale techniques, limiting the bulk-scale in-situ investigations. This thesis focuses on neutron scattering techniques and demonstrates how the utilization of small angle neutron scattering (SANS) techniques and neutron diffraction (ND) in a complementary manner with lab-scale techniques and computational tools can enhance the mechanistic understanding during processing of hard metals and related systems. Some of the presented information within the thesis is unique to neutron scattering experiments. SANS experiments are used for the quantification of nano- and microstructural features including Co-rich binder pocket size, WC grain size, and size and volume fraction of (V,W)Cx interfacial layers. The quantitative data enables us to draw conclusions regarding the mechanism of grain coarsening inhibition in V-doped hard metals at different V additions. The findings indicate that the grain coarsening inhibition in V-doped hard metals originates from reduced WC/Co interface mobility and total driving force for coarsening. The complex nature of structural evolution at sintering temperatures is further investigated by in-situ SANS up to 1500 oC. Our results show that the size and volume, Sedan upptäckten av hårdmetall för cirka 100 år sedan har verktyg gjorda av hårdmetall varit avgörande för tillämpningar inom olika områden såsom borrning av tunnelbanelinjer för mer hållbara städer och bearbetning av nästa generations flygplansmotorer för minskade CO2-utsläpp. Förbättrade egenskaper hos hårdmetallen leder således till ökad effektivitet i olika verktygsoperationer med kortare ledtid, mindre miljöpåverkan och minskade kostnader för till exempel tillverkning. För att skräddarsy den sintrade hårdmetallstrukturen och skapa önskade egenskaper är det viktigt att ha statistiskt representativ experimentell data som uppmätts under förhållanden som efterliknar de verkliga processerna inom industrin. Hittills har dock nano- och mikrostrukturundersökningar av hårdmetaller och relaterade system huvudsakligen varit begränsade till laboratorietekniker, vilket begränsat in-situ-undersökningar av materialens bulk. Den här avhandlingen använder neutronspridningstekniker på olika relevanta hårdmetallsystem och visar på hur lågvinkelspridning (SANS) och neutrondiffraktion (ND) kan komplettera konventionella laboratorietekniker och beräkningsverktyg för att förbättra förståelsen av meknismer som styr materialets utveckling under olika processer. En del av datat som presenteras i avhandlingen kan endast uppnås med hjälp av neutronspridningsexperiment. SANS-experiment används för kvantifiering av nano- och mikrostrukturella egenskaper inklusive mätning av den Co-rika bindefasens storlek, kornstorlek hos WC och storleken och volymsfraktionen av (V,W)Cx-gränsskikt. Den kvantitativa datan gör det möjligt för oss att dra slutsatser angående mekanismen för inhibering av kornförgrovning i V-dopade hårdmetaller vid olika V-tillsatser. Resultaten tyder på att kornförgrovningsinhiberingen i V-dopade hårdmetaller härrör från minskad rörlighet av WC/Co-gränskikt och minskad total drivkraft för förgrovning. Den komplexa karaktären av den strukturell utveckling vid sintringstemperat, Stiftelsen för Strategisk Forskning (SSF): SwedNESS - Sveriges neutronforskarskola (GSn15-0008)

Drill bits equipped with WC-Co cemented carbide buttons offer great performance in many rock drilling applications. Generally, the wear of these buttons against the rock is gradual and moderate, or even slow depending on the rock conditions. However, the Co binder has recently been found to cause health issues and an alternative binder, which does not compromise the performance of the cemented carbide, is needed. In the present work, the performance of WC-Fe and WC-Ni is investigated and compared to the common WC-Co in a sliding test against granite. The results show immediate scrape-off of granite against protruding WC grain edges. Some WC grains crack and fragments are subsequently removed, adding up to loss of entire WC grains. A nanoscale pattern gradually evolves on other WC grains, implying also nanoscale wear. Both WC-Fe and WC-Ni show significantly faster wear initiation and early propagation compared to WC-Co, although the wear characteristics are similar.

As Ti-alloys become more and more utilized the need for efficient and robust manufacturing of Ti-alloy components increase in importance. Ti-alloys are more difficult to machine than e.g. steel, mainly due to their poor thermal conductivity leading to rapid tool wear. The atomic scale processes responsible for this wear is not well understood. Here the focus is turned to the effects of C diffusion out of the tools as a source of the observed wear. A combination of Density Functional Theory (DFT) making use of Harmonic Transition State Theory (HTST), classical Molecular Dynamics (MD) and kinetic Monte Carlo (kMC) is used to investigate C diffusion into and within experimentally observed WC/W interfaces that exists as a consequence of the C depletion. Further, tools are built and used to evaluate interface parameters for large sets of interfaces within the WC/W system to determine which are energetically preferred. The results from the DFT study show stable interfaces with large differences in activation energy between the two most prominent surfaces found in WC materials, namely the basal and prismatic surfaces. Within the WC/W interfaces the diffusion barriers are similar between the two. The classical MD simulations support the view of stable interfaces at the early stages of C depletion. As C is removed this picture shifts to one in which the diffusion barriers are substantially decreased and the difference between the basal and the prismatic interfaces vanish pointing to a process which starts out slow but accelerates as C is continually removed. From the kMC simulations the overall diffusion pre-factor and activation energy is estimated to be D0=1.8x10-8 m2/s and dE=1.24 eV for the investigated [10-10]-I/[100] interface, the kMC simulations also confirm previous results indicating that the diffusion is restricted to the interface region. The investigation and screening of properties for WC/W interfaces show a preference for the W terminated [10-10]-I/[110] and [

In this work, the effect of the test configuration and temperature on the mechanical behaviour of cemented carbides (WC-Co) with different carbide grain sizes (dWC) and cobalt volume fractions (VCo), implying different binder mean free paths ( Co), was studied. The mechanical strength was measured at 600º C with bar-shaped specimens subjected to uniaxial four-point bending (4PB) tests and with disc specimens subjected to biaxial ball-on-three-balls (B3B) tests. The results were analysed within the frame of theWeibull theory and compared with strength measurements performed at room temperature under the same loading conditions. A mechanical degradation greater than 30% was observed when the samples were tested at 600ºC due to oxidation phenomena, but higherWeibull moduli were obtained as a result of narrower defect size distributions. A fractographic analysis was conducted with broken specimens from each test configuration. The number of fragments (Nf) and the macroscopic fracture surface were related to the flexural strength and fracture toughness of WC-Co. For a given number of fragments, higher mechanical strength values were always obtained for WC-Co grades with higher KIc. The observed differences were discussed based on a linear elastic fracture mechanics (LEFM) model, taking into account the effect of the temperature and microstructure of the cemented carbides on the mechanical strength.

Materials are never 100% pure due to the limitation of purification method or manufacturing process. Nor are they perfect, especially under deformation. The present work aims to explore different roles played by the defects in austenitic steels and hard metals. The first focus is iron-manganese (Fe-Mn) based twinning induced plasticity(TWIP) steels which are a category of austenitic materials showing a good combination of high strength and ductility. The planar fault is fundamental for the TWIP mechanism. First, the γ-surface of pure γ-Fe (fcc-Fe) is calculated for different magnetic states. Next, the effects of alloying elements, including Mn,interstitial carbon (C) and nitrogen (N), are addressed. The γ-surface includes several prominent stacking fault energies that are fundamental for, e.g, predicting critical twinning stress and twinnability. The present work compares the γ-surface obtained at different magnetic states, including nonmagnetic (NM), paramagnetic(PM), antiferromagnetic single-layer (AFMI) and double-layer (AFMD) states. The local magnetism significantly influences the γ-surface. In addition, the existing antiferromagnetic (AFM) order results in two different deformation paths inγ-Fe, leading to the generations of superlattice intrinsic stacking fault (SISF) and complex stacking fault (CSF), respectively. The intrinsic stacking fault energy corresponding to SISF is relatively low while its corresponding unstable stacking fault energy is relatively high. The magnetic structures are investigated in the unstable stacking fault and the intrinsic stacking fault configurations via Monte Carlo (MC) simulations. The MC results show that only SISF configuration is favourable, and the two distinctive unstable stacking fault configurations may coexist. The Mn effect on the γ-surface of γ-Fe is studied at AFMI state and the crystal tetragonality is considered. The comparison with experimentally measured stacking fault energy (SFE) dependence on Mn composition s, Järn-Mangan (Fe-Mn)-baserade twinning induced plasticity (TWIP) stål är en kategori av austenitiska material som har en kombination av hög hållfasthet och god duktilitet. För att få en mer tydlig bild av olika roller som spelas av defekter i Fe-Mn-baserade legeringar med ytcentrerad kubisk struktur (fcc), specifikt deras effekter på mekaniska egenskaper och magnetiska strukturer, beräknas först γ- ytan för rent γ-Fe vid olika magnetiska tillstånd. Därefter behandlas effekterna av legeringsämnet mangan och de interstitiella legeringsämnena kol (C) och kväve (N). γ-ytan innehåller flera framstående staplingsfelenergier som är grundläggande för att, till exempel, förutsäga kritisk spänning för tvilllingbildning och twinnability . Vi jämför γ-ytan som erhålls vid olika magnetiska tillstånd, inklusive ickemagnetisk (NM), paramagnetisk (PM), antiferromagnetiskt enkelskikt (AFMI) och dubbelskikt (AFMD). Det har visat sig att det lokala magnetiska momentet väsentligt påverkar γ-ytan. Dessutom resulterar den befintliga antiferromagnetiaka (AFM) ordningen i två olika deformationsvägar i γ-Fe. De två olika deformationsvägarna leder till generering av intrinsiska supergitterstaplingsfel (SISF) respektive komplexa staplingsfel (CSF), där den intrinsiska staplingsfelenergin motsvarande SISF är relativt lägre medan den motsvarande instabila staplingsfelenergin är relativt högre. Vi undersöker sedan de magnetiska strukturerna nära det instabila staplingsfelet och det intrinsiska staplingsfelet med Monte Carlo (MC) simuleringar. Vi fann att närvaron av stapelfel ändrar fördelningen av magnetiska moment för på bulkmaterial. Och i verkligheten är det bara SISF som är gynnsamma med avseende på CSF, men de två distinkta instabila stapelfelkonfigurationerna kan samexistera. Effekten av Mn på γ-ytan för γ-Fe studeras vidare i AFMI-tillståndet och kristall-tetragonaliteten beaktas. Jämförelsen med experimentellt uppmätt staplingsfelsenergi (SFE) beroende av Mn-innehållet visar att AFMI-res

Materials are never 100% pure due to the limitation of purification method or manufacturing process. Nor are they perfect, especially under deformation. The present work aims to explore different roles played by the defects in austenitic steels and hard metals. The first focus is iron-manganese (Fe-Mn) based twinning induced plasticity(TWIP) steels which are a category of austenitic materials showing a good combination of high strength and ductility. The planar fault is fundamental for the TWIP mechanism. First, the γ-surface of pure γ-Fe (fcc-Fe) is calculated for different magnetic states. Next, the effects of alloying elements, including Mn,interstitial carbon (C) and nitrogen (N), are addressed. The γ-surface includes several prominent stacking fault energies that are fundamental for, e.g, predicting critical twinning stress and twinnability. The present work compares the γ-surface obtained at different magnetic states, including nonmagnetic (NM), paramagnetic(PM), antiferromagnetic single-layer (AFMI) and double-layer (AFMD) states. The local magnetism significantly influences the γ-surface. In addition, the existing antiferromagnetic (AFM) order results in two different deformation paths inγ-Fe, leading to the generations of superlattice intrinsic stacking fault (SISF) and complex stacking fault (CSF), respectively. The intrinsic stacking fault energy corresponding to SISF is relatively low while its corresponding unstable stacking fault energy is relatively high. The magnetic structures are investigated in the unstable stacking fault and the intrinsic stacking fault configurations via Monte Carlo (MC) simulations. The MC results show that only SISF configuration is favourable, and the two distinctive unstable stacking fault configurations may coexist. The Mn effect on the γ-surface of γ-Fe is studied at AFMI state and the crystal tetragonality is considered. The comparison with experimentally measured stacking fault energy (SFE) dependence on Mn composition s, Järn-Mangan (Fe-Mn)-baserade twinning induced plasticity (TWIP) stål är en kategori av austenitiska material som har en kombination av hög hållfasthet och god duktilitet. För att få en mer tydlig bild av olika roller som spelas av defekter i Fe-Mn-baserade legeringar med ytcentrerad kubisk struktur (fcc), specifikt deras effekter på mekaniska egenskaper och magnetiska strukturer, beräknas först γ- ytan för rent γ-Fe vid olika magnetiska tillstånd. Därefter behandlas effekterna av legeringsämnet mangan och de interstitiella legeringsämnena kol (C) och kväve (N). γ-ytan innehåller flera framstående staplingsfelenergier som är grundläggande för att, till exempel, förutsäga kritisk spänning för tvilllingbildning och twinnability . Vi jämför γ-ytan som erhålls vid olika magnetiska tillstånd, inklusive ickemagnetisk (NM), paramagnetisk (PM), antiferromagnetiskt enkelskikt (AFMI) och dubbelskikt (AFMD). Det har visat sig att det lokala magnetiska momentet väsentligt påverkar γ-ytan. Dessutom resulterar den befintliga antiferromagnetiaka (AFM) ordningen i två olika deformationsvägar i γ-Fe. De två olika deformationsvägarna leder till generering av intrinsiska supergitterstaplingsfel (SISF) respektive komplexa staplingsfel (CSF), där den intrinsiska staplingsfelenergin motsvarande SISF är relativt lägre medan den motsvarande instabila staplingsfelenergin är relativt högre. Vi undersöker sedan de magnetiska strukturerna nära det instabila staplingsfelet och det intrinsiska staplingsfelet med Monte Carlo (MC) simuleringar. Vi fann att närvaron av stapelfel ändrar fördelningen av magnetiska moment för på bulkmaterial. Och i verkligheten är det bara SISF som är gynnsamma med avseende på CSF, men de två distinkta instabila stapelfelkonfigurationerna kan samexistera. Effekten av Mn på γ-ytan för γ-Fe studeras vidare i AFMI-tillståndet och kristall-tetragonaliteten beaktas. Jämförelsen med experimentellt uppmätt staplingsfelsenergi (SFE) beroende av Mn-innehållet visar att AFMI-res

Materials are never 100% pure due to the limitation of purification method or manufacturing process. Nor are they perfect, especially under deformation. The present work aims to explore different roles played by the defects in austenitic steels and hard metals. The first focus is iron-manganese (Fe-Mn) based twinning induced plasticity(TWIP) steels which are a category of austenitic materials showing a good combination of high strength and ductility. The planar fault is fundamental for the TWIP mechanism. First, the γ-surface of pure γ-Fe (fcc-Fe) is calculated for different magnetic states. Next, the effects of alloying elements, including Mn,interstitial carbon (C) and nitrogen (N), are addressed. The γ-surface includes several prominent stacking fault energies that are fundamental for, e.g, predicting critical twinning stress and twinnability. The present work compares the γ-surface obtained at different magnetic states, including nonmagnetic (NM), paramagnetic(PM), antiferromagnetic single-layer (AFMI) and double-layer (AFMD) states. The local magnetism significantly influences the γ-surface. In addition, the existing antiferromagnetic (AFM) order results in two different deformation paths inγ-Fe, leading to the generations of superlattice intrinsic stacking fault (SISF) and complex stacking fault (CSF), respectively. The intrinsic stacking fault energy corresponding to SISF is relatively low while its corresponding unstable stacking fault energy is relatively high. The magnetic structures are investigated in the unstable stacking fault and the intrinsic stacking fault configurations via Monte Carlo (MC) simulations. The MC results show that only SISF configuration is favourable, and the two distinctive unstable stacking fault configurations may coexist. The Mn effect on the γ-surface of γ-Fe is studied at AFMI state and the crystal tetragonality is considered. The comparison with experimentally measured stacking fault energy (SFE) dependence on Mn composition s, Järn-Mangan (Fe-Mn)-baserade twinning induced plasticity (TWIP) stål är en kategori av austenitiska material som har en kombination av hög hållfasthet och god duktilitet. För att få en mer tydlig bild av olika roller som spelas av defekter i Fe-Mn-baserade legeringar med ytcentrerad kubisk struktur (fcc), specifikt deras effekter på mekaniska egenskaper och magnetiska strukturer, beräknas först γ- ytan för rent γ-Fe vid olika magnetiska tillstånd. Därefter behandlas effekterna av legeringsämnet mangan och de interstitiella legeringsämnena kol (C) och kväve (N). γ-ytan innehåller flera framstående staplingsfelenergier som är grundläggande för att, till exempel, förutsäga kritisk spänning för tvilllingbildning och twinnability . Vi jämför γ-ytan som erhålls vid olika magnetiska tillstånd, inklusive ickemagnetisk (NM), paramagnetisk (PM), antiferromagnetiskt enkelskikt (AFMI) och dubbelskikt (AFMD). Det har visat sig att det lokala magnetiska momentet väsentligt påverkar γ-ytan. Dessutom resulterar den befintliga antiferromagnetiaka (AFM) ordningen i två olika deformationsvägar i γ-Fe. De två olika deformationsvägarna leder till generering av intrinsiska supergitterstaplingsfel (SISF) respektive komplexa staplingsfel (CSF), där den intrinsiska staplingsfelenergin motsvarande SISF är relativt lägre medan den motsvarande instabila staplingsfelenergin är relativt högre. Vi undersöker sedan de magnetiska strukturerna nära det instabila staplingsfelet och det intrinsiska staplingsfelet med Monte Carlo (MC) simuleringar. Vi fann att närvaron av stapelfel ändrar fördelningen av magnetiska moment för på bulkmaterial. Och i verkligheten är det bara SISF som är gynnsamma med avseende på CSF, men de två distinkta instabila stapelfelkonfigurationerna kan samexistera. Effekten av Mn på γ-ytan för γ-Fe studeras vidare i AFMI-tillståndet och kristall-tetragonaliteten beaktas. Jämförelsen med experimentellt uppmätt staplingsfelsenergi (SFE) beroende av Mn-innehållet visar att AFMI-res

In this work, the effect of the test configuration and temperature on the mechanical behaviour of cemented carbides (WC-Co) with different carbide grain sizes (dWC) and cobalt volume fractions (VCo), implying different binder mean free paths ( Co), was studied. The mechanical strength was measured at 600º C with bar-shaped specimens subjected to uniaxial four-point bending (4PB) tests and with disc specimens subjected to biaxial ball-on-three-balls (B3B) tests. The results were analysed within the frame of theWeibull theory and compared with strength measurements performed at room temperature under the same loading conditions. A mechanical degradation greater than 30% was observed when the samples were tested at 600ºC due to oxidation phenomena, but higherWeibull moduli were obtained as a result of narrower defect size distributions. A fractographic analysis was conducted with broken specimens from each test configuration. The number of fragments (Nf) and the macroscopic fracture surface were related to the flexural strength and fracture toughness of WC-Co. For a given number of fragments, higher mechanical strength values were always obtained for WC-Co grades with higher KIc. The observed differences were discussed based on a linear elastic fracture mechanics (LEFM) model, taking into account the effect of the temperature and microstructure of the cemented carbides on the mechanical strength.

In this work, the effect of the test configuration and temperature on the mechanical behaviour of cemented carbides (WC-Co) with different carbide grain sizes (dWC) and cobalt volume fractions (VCo), implying different binder mean free paths ( Co), was studied. The mechanical strength was measured at 600º C with bar-shaped specimens subjected to uniaxial four-point bending (4PB) tests and with disc specimens subjected to biaxial ball-on-three-balls (B3B) tests. The results were analysed within the frame of theWeibull theory and compared with strength measurements performed at room temperature under the same loading conditions. A mechanical degradation greater than 30% was observed when the samples were tested at 600ºC due to oxidation phenomena, but higherWeibull moduli were obtained as a result of narrower defect size distributions. A fractographic analysis was conducted with broken specimens from each test configuration. The number of fragments (Nf) and the macroscopic fracture surface were related to the flexural strength and fracture toughness of WC-Co. For a given number of fragments, higher mechanical strength values were always obtained for WC-Co grades with higher KIc. The observed differences were discussed based on a linear elastic fracture mechanics (LEFM) model, taking into account the effect of the temperature and microstructure of the cemented carbides on the mechanical strength.

Laser beam welding of hard metal to steel offers multiple advantages regarding resource saving, mechanical strength of the joint and automation capability. The present work focuses on the fundamental research and development of the laser based welding process of tungsten carbide-cobalt hard metals with a tempering steel. Metallurgical analysis of the welding process showed that the formation of intermetallic and/or intermediate phases has a significant influence on the properties and mechanical strength of the dissimilar joint. The amount of molten hard metal in the steel melt bath plays a key role for the formation of the different phases. Therefore, a new parameter dy was defined, which correlates with the hard metal content in the melt pool. It is shown that for hard metals with 12 wt.% of cobalt binder, the phase transformation in the weld seam starts with a relative hard metal content of 10 vol.%. This threshold is dependent on the relative cobalt concentration in the hard metal. The tungsten carbide grain size has a low influence on the phase transformation in the weld seam. Steel melt pools with hard metal content lower than 10 vol.% show under metallographic observation a martensitic/bainitic microstructure. Simulation of the stress formation in the joint showed that due to the volume expansion of martensite during the transformation, tensile stress in the hard metal part was formed. Under shear load, these tensile stresses compensate with the induced compressive stresses and results an almost stress free interface. High shear strengths of the dissimilar joints are possible. A higher percentage of hard metal melting during the welding process increases the carbon and tungsten content in the melt bath. Consequently, the martensite start temperature decreases significantly. When the initiating temperature for martensite transformation falls under room temperature, the weld seam transforms into an austenitic microstructure. Because of the missing volume expansi

Laser beam welding of hard metal to steel offers multiple advantages regarding resource saving, mechanical strength of the joint and automation capability. The present work focuses on the fundamental research and development of the laser based welding process of tungsten carbide-cobalt hard metals with a tempering steel. Metallurgical analysis of the welding process showed that the formation of intermetallic and/or intermediate phases has a significant influence on the properties and mechanical strength of the dissimilar joint. The amount of molten hard metal in the steel melt bath plays a key role for the formation of the different phases. Therefore, a new parameter dy was defined, which correlates with the hard metal content in the melt pool. It is shown that for hard metals with 12 wt.% of cobalt binder, the phase transformation in the weld seam starts with a relative hard metal content of 10 vol.%. This threshold is dependent on the relative cobalt concentration in the hard metal. The tungsten carbide grain size has a low influence on the phase transformation in the weld seam. Steel melt pools with hard metal content lower than 10 vol.% show under metallographic observation a martensitic/bainitic microstructure. Simulation of the stress formation in the joint showed that due to the volume expansion of martensite during the transformation, tensile stress in the hard metal part was formed. Under shear load, these tensile stresses compensate with the induced compressive stresses and results an almost stress free interface. High shear strengths of the dissimilar joints are possible. A higher percentage of hard metal melting during the welding process increases the carbon and tungsten content in the melt bath. Consequently, the martensite start temperature decreases significantly. When the initiating temperature for martensite transformation falls under room temperature, the weld seam transforms into an austenitic microstructure. Because of the missing volume expansi

Laser beam welding of hard metal to steel offers multiple advantages regarding resource saving, mechanical strength of the joint and automation capability. The present work focuses on the fundamental research and development of the laser based welding process of tungsten carbide-cobalt hard metals with a tempering steel. Metallurgical analysis of the welding process showed that the formation of intermetallic and/or intermediate phases has a significant influence on the properties and mechanical strength of the dissimilar joint. The amount of molten hard metal in the steel melt bath plays a key role for the formation of the different phases. Therefore, a new parameter dy was defined, which correlates with the hard metal content in the melt pool. It is shown that for hard metals with 12 wt.% of cobalt binder, the phase transformation in the weld seam starts with a relative hard metal content of 10 vol.%. This threshold is dependent on the relative cobalt concentration in the hard metal. The tungsten carbide grain size has a low influence on the phase transformation in the weld seam. Steel melt pools with hard metal content lower than 10 vol.% show under metallographic observation a martensitic/bainitic microstructure. Simulation of the stress formation in the joint showed that due to the volume expansion of martensite during the transformation, tensile stress in the hard metal part was formed. Under shear load, these tensile stresses compensate with the induced compressive stresses and results an almost stress free interface. High shear strengths of the dissimilar joints are possible. A higher percentage of hard metal melting during the welding process increases the carbon and tungsten content in the melt bath. Consequently, the martensite start temperature decreases significantly. When the initiating temperature for martensite transformation falls under room temperature, the weld seam transforms into an austenitic microstructure. Because of the missing volume expansi

During metal cutting, high temperatures of several hundred-degree Celsius occur locally at the cutting edge, which greatly impacts tool wear and life. Not only the cutting parameters, but also the tool material’s properties influence the arising cutting temperature which in turn alters the mechanical properties of the tool. In this study, the hardness and thermal conductivity of cemented tungsten carbides were investigated in the range between room temperature and 1000 °C. The occurring temperatures close to the cutting edge were measured with two color pyrometry. The interactions between cemented carbide tool properties and cutting process parameters, including cutting edge rounding, are discussed. The results show that cemented carbides with higher thermal conductivities lead to lower temperatures during cutting. As a result, the effective hardness at the cutting edge can be strongly influenced by the thermal conductivity. The differences in hardness measured at room temperature can be equalized or evened out depending on the combination of hardness and thermal conductivity. This in turn has a direct influence on tool wear. Wear is also influenced by the softening of the workpiece, so that higher cutting temperatures can lead to less wear despite the same effective hardness.

Milling of ferrous metals is usually performed by applying cemented carbide tools due to their high hardness, temperature and wear resistance. Recently, ceramic tool materials have been on the rise and enhanced the efficiency in machining. As ceramics are brittle-hard materials, tool manufacturing requires a sound knowledge in order to meet the tool requirements such as sharp cutting edges and wear resistance. In this study, milling tools made of the high performance ceramic SiAlON were compared to tools made from cemented carbide. For both tool materials, the influence of a prepared cutting edge was investigated. Both the tool manufacturing process and the cutting edge preparation processes are presented, followed by the application of those tools within milling experiments. In order to evaluate the efficiency of both tool types, the cutting forces and the cumulative process energy demand were analyzed. Additionally, surface roughness of the machined workpieces and tool wear were examined. It was found that the ceramic tools, although process forces were higher than for cemented carbide tools, exhibited by far lower energy consumption, less tool wear and finally generated lower surface roughness. © 2020, The Author(s).

The correlation between the damage induced under cyclic contact fatigue and their electrochemical behavior (anodic polarization curves) for different WC-Co-based cemented carbides grades was investigated at the macrometric and micrometric length scale. Under both, dry (i.e. air atmosphere) and wet (cutting lubricant fluid) conditions, the crack path propagates near the carbide/metallic binder interface, resulting in tortuous cracks of several micrometers. Despite the alkaline conditions imposed by the cutting fluid (pH 9.2), the cobalt binder is preferentially dissolved, and the carbide-skeleton keeps stable. The presence of cutting fluid in the contact fatigue zone changes the morphology of the cracks due to the partial dissolution of the binder phase. The addition of chromium to the WC-Co composition enhances corrosion resistance of the metallic binder phase resulting in reduced damage of the cemented carbides in environmental assisted cyclic contact fatigue conditions., Peer Reviewed, Postprint (author's final draft)

The main goal of the present work is to study the influence of the microstructure on the corrosion behavior of cemented carbides WC-Co in two corrosive media. Corrosion kinetics were determined by immersion tests while the electrochemical evolution of the Surface was analyzed using impedance testing. Damage tolerance to corrosion was evaluated by assessing fracture strength on specimens previously subjected to corrosion. Results pointed out that for both grades the corrosion rate was higher in seawater, being more significant for the grade with a medium grain size. The corrosion phenomenon that took place in both media was caused by the oxidation reaction of cobalt. In seawater, the polarization resistance decreased for both grades whereas in mine water increased, due to the formation of a layer of corrosion products, which slowed down the cobalt dissolution process in Surface. In both media, a greater strength loss of the ultrafine grades was evidenced., Peer Reviewed, Postprint (author's final draft)