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High-entropy carbides (HEC) are a class of promising new hard phases for a sustainable improvement of hardmetal properties. In this work, hardmetals of the HEC (Ta,Nb,Ti,V,W)C were studied with two typical binder volume fractions of 16 and 24 vol-% consisting of Co, Ni and FeNi. The sintering behaviour, microstructure, phase composition, magnetic and mechanical properties are discussed and are compared to a conventional WC-Co hardmetal. It was shown that the HEC has a high-phase stability and that dense hardmetals with promising mechanical properties were obtained.

Excellent thermal conductivity is beneficial for the fast heat release during service of cemented carbides. Thus, thermal conductivity is a significant property of cemented carbides, considerably affecting their service life. Still, there is a lack of systematic investigation into the thermal conductivity of two-phase WC-Co-Ni cemented carbides. To remedy this situation, we integrated experiments and models to study its thermal conductivity varying the phase composition, temperature and WC grain size. To conduct the experiments, WC-Co-Ni samples with two-phase structure were designed via the CALPHAD (Calculation of Phase Diagrams) approach and then prepared via the liquid-phase sintering process. Key thermal conductivity measurements of these prepared samples were then taken via LFA (Laser Flash Analysis). As for modeling, the thermal conductivities of (Co, Ni) binder phase and WC hard phase were firstly evaluated through our previously developed models for single-phase solid solutions. Integrating the present key measurements and models, the values of ITR (Interface Thermal Resistance) between WC hard phase and (Co, Ni) binder phase were evaluated and thus the model to calculate thermal conductivity of two-phase WC-Co-Ni was established. Meanwhile, this model was verified to be reliable through comparing the model-evaluated thermal conductivities with the experimental data. Furthermore, using this developed model, the thermal conductivity of two-phase WC-Co-Ni varying with phase-fraction, temperature and grain size of WC was predicted, which can contribute to its design for obtaining desired thermal conductivities.

International audience; Integrated Computational Materials Engineering (ICME) has proved to be an efficient tool for understanding 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 processing 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 interplay happening along microstructural evolution. A better understanding of these underlaying mechanisms 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.

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.

21. CIRP Conference on Electro Physical and Chemical Machining, ISEM XXI, Zurich, Switzerland, 14 Jun 2022 - 17 Jun 2022; Procedia CIRP 113, 53-58 (2022). doi:10.1016/j.procir.2022.09.119 special issue: "21st CIRP Conference on Electro Physical and Chemical Machining, ISEM XXI June, 14 to 17, 2022 in Zurich / edited by Konrad Wegener, Stefan Fabbro, Paulo Matheus Borges", Published by Elsevier, Amsterdam [u.a.]

Cemented carbides WC-Co feature high mechanical properties and outstanding wear resistance. Traditional grinding of such hard workpiece features low material removal rate and diminished tool life. Notwithstanding that, even if, proper cooling fluid is applied; abrasive machining of cemented carbides characterizes poor efficiency. The aim of this study was to investigate the issue of WEDM of the cemented carbides WC-Co with two alternative materials of the wire electrodes applied. The presented experimental surface layer geometry measurements was carried out on a modern profilometer MITUTOYO SV 3200. Especially, WEDM results with wire flushing and in immersion were compared. Investigated were the effects of such input parameters as the pulse width and the time between two pulses on the output parameters such as area cutting efficiency, workpiece surface roughness in 2D and 3D. Analysing SEM microphotographs the surface layer defects after WEDM, cobalt depletion and pitting was discoursed. The analysed results provided WEDM of WC-Co cemented carbides with molybdenum wire electrode as seventy one percent less efficient and higher roughness was obtained for the same number of passes. The lowest height of the roughness on the surface after cutting with molybdenum wire amounted to Ra and Sa = 3.5 μm. Such roughness involves a 25 μm deep undesirable heat affected zone. WEDM with equal number of passes and brass wire resulted in roughness Ra and Sa =0,9 μm. In further research, an endeavour should be directed to examine different water and hydrocarbons derivative dielectrics impact on the surface layer structure and chemical composition of the machined WC-Co carbides.

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 μm). 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.

The concept “structural strength of tool materials” got further development. The refusals of cemented carbide cutting plates, when heavy machining were analyzed. It was shown that 70…80% of refusals are the microchipping of cutting edges, tool cutting part chipping, cutting plate macrofracture. To assess cutting plate total carrying capacity and the influence of different methods of cemented carbides modification, bending tests were held. Local fracture resistance and damageability of cutting edge were assessed under its continuous scanning.

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)

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

Tungsten carbide (WC) is the most important tungsten compound, and the main component of WC-Co cermet composites. WC-Co are widely used engineering materials due to the combination of high hardness and strength of tungsten carbide with the toughness and plasticity of the metallic binder. The direct synthesis of WC from tungsten concentrate containing ∼70% WO3 has been achieved by carbothermic reduction. Mineral/carbon black mixtures were prepared by planetary ball milling and subjected to annealing at 1150 °C in flowing Ar. Specific leaching treatments have been developed to remove foreign phases and obtain pure WC powders. This new process allows about 50% energy saving, -34% CO2 emissions, and significantly lower amounts of industrial waste, with respect to the classical hydrometallurgical tungsten extraction and subsequent pyrometallurgical WC synthesis, widely used in tungsten industry. WC powders obtained by carbothermic reduction of the mineral were employed to prepare sintered WC-8 wt %Co samples that showed high density (>99%), hardness (1490 HV), and toughness (14.6 MPa·m1/2). These findings demonstrate, for the first time, that the carbothermic reduction of tungsten concentrates does represent a viable process for energy efficient and sustainable synthesis of WC powders to be used in the production of cemented carbides.

CoNiFeCr high entropy alloy (HEA) was used as a binder in cemented carbides for developing a new high-performance binder. The microstructure of WC-HEA cemented carbides with different binder components and carbon contents was subsequently studied. It was observed that the (Cr,W)C phase precipitated at the WC/HEA interface, and a coherent interface with a low degree of misfit was formed between WC and (Cr,W)C, thereby resulting in a significant reduction in the interfacial energy and stress concentration. The (Cr,W)C phase exerted a pinning force (Zener-drag) on the moving grain boundaries, which effectively inhibited the growth of WC grains. As a result, compared with WC-Co, WC-CoNiFeCr had smaller WC grain size, smoother grain shape and larger mean free path (MFP) of the binder, which resulted in slightly lower hardness and higher transverse rupture strength (TRS) and fracture toughness. The lower limit of carbon content in WC-CoNiFeCr was higher than that of WC-Co. With the addition of Ni, the width of the two-phase region became wider, whereas the width of the two-phase region became narrower with the addition of Fe and Cr.

Compositional effects on the dry sliding wear resistance of micrometer-grained WC-10 wt.%(Co+Fe+Ni) cemented carbides pressureless sintered with 2 wt.% Ni but different Fe/Co ratios were investigated. Their microstructures are very similar except for the contiguity of the WC grains, which increased with increasing Fe/Co ratio. Also, these cemented carbides are all almost fully dense, but with the degree of residual porosity exhibiting a complex trend with increasing Fe/Co ratio (first decreasing and then increasing). The greatest densification was reached for an Fe/Co ratio of 1. The reverse trend was observed for the hardness, which reached HV10=1090 kg/mm2 for Fe/Co = 1, indicative that it is dictated essentially by the porosity. The wear resistance correlated inversely with the porosity (and thus directly with the hardness), so that the densest (and thus the hardest) of these cemented carbides (the one sintered with a Fe/Co ratio of 1) also exhibited the lowest coefficients of friction, the lowest specific wear rates, and the lowest microstructural damage. The wear mode was abrasion, with the wear mechanism being plastic deformation and especially fracture. Thus, optimization of the wear resistance of WC-(Co+Fe+Ni) cemented carbides for tribological applications is feasible by a judicious design of their binder composition.

ispartof: MATERIALS CHARACTERIZATION vol:187 status: published

Cemented carbides are metallic composites consisting of a WC hard phase and a ductile binder, usually Co-based, produced by powder metallurgy and sintering. Cemented carbides are an essential part of modern material and manufacturing processes. However, Co powder is classified as a carcinogenic material with serious health hazards, and most virgin Co reservoirs are located in conflict regions. In addition, there are monopolies in the market for pure tungsten. Therefore, reducing the consumption of cobalt or replacing it with other non-hazardous elements would increase the sustainability of cemented carbide production. Furthermore, advances in production technology can help overcome raw material limitations. One such advancement is non-homogeneous structures and properties for optimization of microstructure which is the topic of this thesis. Integrated computational materials engineering (ICME) and its complementary tools, calculation of phase diagram (CALPHAD), and ab-initio modeling are strong tools that bridge experimentation and modeling. In this thesis, a framework for the material design of non-homogeneous cemented carbides is proposed and tested using these computational tools. The workflow of the material design of non-homogeneous microstructure and properties were studied on different length scales. Atomistic modeling with density functional theory (DFT), ab-initio molecular dynamics (AIMD), and generalized hydrodynamics (GHD) were used to model the viscosity of liquid Co binder. In addition, the mobility of Ti and Fe in disordered BCC TiFe alloy was assessed using new experimental data from the diffusion couple experiments and an electron probe micro-analyzer (EPMA). These two studies were conducted to complete the data necessary to study cemented carbides’ processing and performance. The other studied phenomenon studied by experimentation and modeling is the formation of the gradient zone and the γ cone structure. In addition, a phenomenological model for liquid phase migration (LPM) was created and implemented using the homogenization approach. The LPM pro- cess was studied experimentally and modeled with the YAPFI software. A study of these performers was necessary to link processing and microstructure. On the performance side, the chemical interaction between cutting tools and Ti alloys was studied in detail through experimentation and modeling of diffusion. In addition, hardness and toughness models were applied to predict the longevity of studied cemented carbides. Finally, by applying ICME and material design, a high entropy alloy (HEA) alternative to Co binder was designed, produced, and tested. The research presented in this dissertation attempts to fill the gaps in the material design workflow of cemented carbides by developing new tools and methods based on ICME and CALPHAD paradigms. This goal is achieved by studying different length scales, processing methods, microstructure, properties, and performance of cemented carbides. Hårdmetaller är metalliska kompositer som består av en hård fas, oftast WC, och ett segt bindemedel, vanligtvis Co-baserat, framställt genom pulvermetal- lurgi och sintring. Hårdmetaller är en väsentlig del av de flesta produktions- processer. Emellertid är Co-pulver klassificerat som ett cancerframkallande material med allvarliga hälsorisker, och de flesta jungfruliga Co-reservoarer finns i konfliktområden. Dessutom finns det monopol på marknaden för ren volfram. Därför skulle en minskning av förbrukningen av kobolt eller att ersät- ta den med andra ofarliga ämnen öka hållbarheten i produktionen av hårdme- tall. Dessutom kan framsteg inom produktionsteknik hjälpa till att övervin- na råvarubegränsningar. Ett sådant framsteg är “icke-homogena” strukturer och beräkiningsverktyg för optimering av produktmikrostruktur som är äm- net för denna avhandling. “Integrated Computational Materials Engineering (ICME)” och dess komplementärar verktyg, beräkning av fasdiagram (CALP- HAD) och ab-initio modellering, är verktyg som överbryggar experiment och modellering. Med hjälp av dessa verktyg föreslås och testas ett ramverk för materialdesign av icke-homogena hårdmetaller i denna avhandling. Arbetsflödet för materialdesign av icke-homogen mikrostruktur och egen- skaper studerades påolika längdskalor. Atomistisk modellering med densitets- funktionsteori (DFT), ab-initio molekylär dynamik (AIMD) och generaliserad hydrodynamik (GHD) användes för att modellera viskositeten hos flytande Co-bindemedel. Rörligheten för Ti och Fe i oordnad BCC TiFe utvärderades med hjälp av nya experimentella data som samlats in från diffusionsparexpe- rimentet och EPMA-analys. Dessa två studier syftade till att komplettera de data som är nödvändiga för att studera hårdmetalls bearbetning och prestan- da. Bildandet av gradientzonen och γ-konstrukturen modellerades och utvär- derades experimentellt. En fenomenologisk modell för flytande fasmigrering (“ Liquid Phase Migration”, LPM) skapades och implementerades med hjälp av homogeniseringsmetoden. LPM-processen studerades experimentellt och mo- dellerades med YAPFI-mjukvaran. En studie av dessa processer var nödvän- dig för att koppla samman bearbetning och mikrostruktur. På prestandasidan studerades kemisk interaktion mellan skärverktyg och Ti-legeringar i detalj genom experiment och diffusionsmodellering. Dessutom användes hårdhets- och seghetsmodeller för att förutsäga hårdmetallers prestanda. Slutligen, med tillämpning av ICME och materialdesign, designades, producerades och tes- tades ett alternativt bindemedel med bestående av högentropilegering. ICME och CALPHAD genomsyrade hela forskningsprojekted. Studierna på olika längdskalor hjälpte till att bättre förstå bearbetning, mikrostruktur, egenska- per och prestanda hos hårdmetaller. Dessutom har nya verktyg och metoder utvecklats för att fylla luckorna i materialdesignens arbetsflöde för hårdme- taller. Hårdmetaller är metalliska kompositer som består av en hård fas, oftast WC, och ett segt bindemedel, vanligtvis Co-baserat, framställt genom pulvermetal- lurgi och sintring. Hårdmetaller är en väsentlig del av de flesta produktions- processer. Emellertid är Co-pulver klassificerat som ett cancerframkallande material med allvarliga hälsorisker, och de flesta jungfruliga Co-reservoarer finns i konfliktområden. Dessutom finns det monopol på marknaden för ren volfram. Därför skulle en minskning av förbrukningen av kobolt eller att ersät- ta den med andra ofarliga ämnen öka hållbarheten i produktionen av hårdme- tall. Dessutom kan framsteg inom produktionsteknik hjälpa till att övervin- na råvarubegränsningar. Ett sådant framsteg är “icke-homogena” strukturer och beräkiningsverktyg för optimering av produktmikrostruktur som är äm- net för denna avhandling. “Integrated Computational Materials Engineering (ICME)” och dess komplementärar verktyg, beräkning av fasdiagram (CALP- HAD) och ab-initio modellering, är verktyg som överbryggar experiment och modellering. Med hjälp av dessa verktyg föreslås och testas ett ramverk för materialdesign av icke-homogena hårdmetaller i denna avhandling. Arbetsflödet för materialdesign av icke-homogen mikrostruktur och egen- skaper studerades påolika längdskalor. Atomistisk modellering med densitets- funktionsteori (DFT), ab-initio molekylär dynamik (AIMD) och generaliserad hydrodynamik (GHD) användes för att modellera viskositeten hos flytande Co-bindemedel. Rörligheten för Ti och Fe i oordnad BCC TiFe utvärderades med hjälp av nya experimentella data som samlats in från diffusionsparexpe- rimentet och EPMA-analys. Dessa två studier syftade till att komplettera de data som är nödvändiga för att studera hårdmetalls bearbetning och prestan- da. Bildandet av gradientzonen och γ-konstrukturen modellerades och utvär- derades experimentellt. En fenomenologisk modell för flytande fasmigrering (“ Liquid Phase Migration”, LPM) skapades och implementerades med hjälp av homogeniseringsmetoden. LPM-processen studerades experimentellt och mo- dellerades med YAPFI-mjukvaran. En studie av dessa processer var nödvän- dig för att koppla samman bearbetning och mikrostruktur. På prestandasidan studerades kemisk interaktion mellan skärverktyg och Ti-legeringar i detalj genom experiment och diffusionsmodellering. Dessutom användes hårdhets- och seghetsmodeller för att förutsäga hårdmetallers prestanda. Slutligen, med tillämpning av ICME och materialdesign, designades, producerades och tes- tades ett alternativt bindemedel med bestående av högentropilegering. ICME och CALPHAD genomsyrade hela forskningsprojekted. Studierna på olika längdskalor hjälpte till att bättre förstå bearbetning, mikrostruktur, egenska- per och prestanda hos hårdmetaller. Dessutom har nya verktyg och metoder utvecklats för att fylla luckorna i materialdesignens arbetsflöde för hårdme- taller. Sintering of non-homogeneous structures

The electrochemical corrosion performance of WC-12 wt% Co in coating and bulk forms has been evaluated in a 3.56 wt% NaCl solution. The coatings were deposited by means of thermal spray techniques, i.e., cold gas spraying (CGS) and high-velocity air fuel (HVAF) spraying, while bulks with different WC sizes were manufactured by conventional pressing and sintering. Microstructural characterizations and phase composition determinations were carried out using scanning electron microscopy and X-ray diffraction. Differences in WC grain size and morphology, carbide dissolution, and cobalt binder phase transformation are discussed according to the inherent characteristics of each processing method. Together with surface roughness (polished/as-sprayed), these features have been observed to directly affect the electrochemical corrosion performance. Electrochemical measurements (open circuit potential, polarization resistance, electrochemical impedance spectroscopy, and polarization curves) showed that the as-sprayed CGS coating presented an electrochemical behavior similar to those of the bulk materials. This was attributed to the higher metallic character of this coating in comparison to that of the HVAF coating. The polished HVAF coating showed anodic activity lower than those of the bulk samples, most likely due to the presence of cobalt–tungsten carbide phases and eventually the lower amount of Co available for dissolution. Finally, the as-sprayed HVAF coating showed very high resistivity due to the presence of surface oxides generated during the deposition process. publishedVersion

The purpose of this study is to verify how the carbon doping of the WC-Co cemented carbide (CC) affected their structure before their processing by hot isostatic pressing (HIP) technology. The samples for this experiment were fabricated by selective laser melting technology (SLM) using a YAG fiberl aser with a power of P = 40 W and a scanning speed of 83 mm/s. The subsequent carbon doping process was performed in a chamber furnace at 900 °C for 1, 4 and 12 h. The HIP was performed at 1,390°C and pressures of 40 MPa, 80 MPa and 120 MPa. The changes induced in the structures were evaluated using X-ray diffraction and various microscopic methods. X-ray diffraction analysis showed that the structure of the samples after SLM consisted of WC, W2C, Co4W2C and Co phases. As a result of the increase in the carbon content in the structure of the samples, the transition carbide W2C and structural phase Co4W2C decayed. Their decay was manifested by the coarsening of the minor alpha phase (WC), which occurred both during the carburizing process and during the subsequent processing using HIP. In the samples in which the structure was carburized prior to HIP, only the structural phases WC and Co were observed in most cases.The results confirm that it is possible to increase the homogeneity of the CC structure and thus its applicability in practice by additional carburization of the sample structure with subsequent processing by HIP technology. The purpose of this study is to verify how the carbon doping of the WC-Co cemented carbide (CC) affected their structure before their processing by hot isostatic pressing (HIP) technology. The samples for this experiment were fabricated by selective laser melting technology (SLM) using a YAG fiberl aser with a power of P = 40 W and a scanning speed of 83 mm/s. The subsequent carbon doping process was performed in a chamber furnace at 900 °C for 1, 4 and 12 h. The HIP was performed at 1,390°C and pressures of 40 MPa, 80 MPa and 120 MPa. The changes induced in the structures were evaluated using X-ray diffraction and various microscopic methods. X-ray diffraction analysis showed that the structure of the samples after SLM consisted of WC, W2C, Co4W2C and Co phases. As a result of the increase in the carbon content in the structure of the samples, the transition carbide W2C and structural phase Co4W2C decayed. Their decay was manifested by the coarsening of the minor alpha phase (WC), which occurred both during the carburizing process and during the subsequent processing using HIP. In the samples in which the structure was carburized prior to HIP, only the structural phases WC and Co were observed in most cases.The results confirm that it is possible to increase the homogeneity of the CC structure and thus its applicability in practice by additional carburization of the sample structure with subsequent processing by HIP technology.

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.

As a backbone to the cutting tools and rock drilling industry, cemented carbides have been used widely due to their high hardness and wear resistance. Most commercially used cemented carbides contain a hard phase made of Tungsten carbide (WC) and a binder phase which is generally ductile. Lately, a secondary hard phase is desired by replacing W in WC partially with one or more metal substitutes such as Ti, V, Ta, Cr and Zr to better its mechanical properties. Some of these carbides are observed to exhibit unusual microstructures during ageing. For example, (Ti,Zr)C present along with WC, has been observed to undergo phase separation from a supersaturated phase, called $\gamma$, to Ti-rich and Zr-rich domains leaving behind an array of precipitates morphologically manifesting as lamellae. This phase separation process has been termed as discontinuous precipitation(DP) as it resembles the classical DP reaction observed in certain binary and multi-component systems. The behaviour comes from the presence of a miscibility gap in the carbide Ref. Borgh et al. 2014 and Ma et al. 2016 due to which the usual response of the system should be to undergo spinodal decomposition(SD), however, the carbide chooses a different path which questions the governing mechanism behind its decomposition process. Several factors are believed to affect such a process and one of such factors is the strain energy, which is generated due to the difference in lattice parameters of the separating phases. When compared to a different miscibility gap system, such as Fe-Cr, where the strain energy is quite low and the response is SD. Other factors such as grain boundary diffusion, atomic mobility, and gradient energy coefficient (κ) are also believed to have an effect on the decomposition process. Therefore, a thorough investigation of the factors is required and, a powerful tool to study the spatio-temporal evolution of the microstructure such as the phase field method, should be used. According to some experiments the lamellae are generally observed to nucleate at grain boundaries and later grow with the help of grain boundary migration Ref. Borgh et al. 2014. The moving grain boundary leaves behind a series of alternate strands of Ti and Zr rich phases. The growth mechanism behind the moving boundary is believed to be assisted by diffusion of solutes along the grain boundary and generation of the elastic strain energy by it. The phenomenon is commonly known as diffusion induced grain boundary migration(DIGM) and it is believed to be a key part of DP Ref. Hillert and Purdy 1977 and Chongmo and Hillert 1981. In order to recreate DIGM and DP an energetic coupling between the mole fraction and phase field variable is required so that it accounts for the generated strain energy during the process. The main focus of this thesis will be to develop a phase field model accounting for such coupling which will predict DIGM in binary systems and use it further as a medium to model DP in (Ti,Zr)C. The model for DP could be used to predict and control its formation as its occurrence prone to increase the hardness of the carbides. Therefore, it can be used as a tool to design alloys and develop better alternatives. The alternatives could be used to prevent DP in the carbides which could be done by using different metal substitutes that will prefer SD over DP or vice versa. Som en ryggrad till skärande verktyg och bergborrningsindustrin har hårdmetaller använts i stor utsträckning på grund av deras höga hårdhet och slitstyrka. De flesta kommersiellt använda hårdmetaller innehåller en hård fas gjord av volframkarbid (WC) och en bindefas som vanligtvis är formbar. På senare tid önskas en sekundär hård fas genom att ersätta W i WC delvis med en eller flera metallersättningar såsom Ti, V, Ta, Cr och Zr för att förbättra dess mekaniska egenskaper. De nyutvecklade karbiderna observeras ofta uppvisa ovanliga mikrostrukturer under åldrandet. Till exempel har (Ti,Zr)C närvarande tillsammans med WC observerats genomgå fasseparation från en övermättad fas, kallad , till Ti-rika och Zr-rika domäner som lämnar efter sig en rad fällningar som morfologiskt manifesterar sig som lameller. Denna fasseparationsprocess har betecknats som diskontinuerlig utfällning (DP) eftersom den liknar den klassiska DP-reaktionen som observeras i vissa binära och flerkomponentsystem. Beteendet kommer från närvaron av ett blandbarhetsgap i karbiden Ref. Borgh et al. 2014, Maet al. 2016 på grund av vilket systemets vanliga reaktion bör vara att genomgå spinodal nedbrytning (SD), men karbiden väljer en annan väg vilket ifrågasätter styrande mekanism bakom dess nedbrytningsprocess. Flera faktorer tros påverka en sådan process och en av sådana faktorer är töjningsenergin, som genereras på grund av skillnaden i gitterparametrar för de separerande faserna. Jämfört med ett annat blandbarhetsgapsystem, såsom Fe-Cr, är töjningsenergin i allmänhet ganska låg och responsen är SD. Andra faktorer såsom korngränsdiffusion, atomrörlighet och gradientenergikoefficient () tros också ha en inverkan på nedbrytningsprocessen. Därför krävs en grundlig undersökning av faktorerna och ett kraftfullt verktyg för att studera den spatio-temporala utvecklingen av mikrostrukturen, såsom fasfältsmetoden, bör användas. Enligt vissa experiment observeras lamellerna i allmänhet bilda kärnor vid korngränserna och senare växa med hjälp av korngränsmigrering Ref. Borgh et al. 2014. Den rörliga korngränsen lämnar efter sig en serie omväxlande strängar av Ti- och Zr-rika faser. Tillväxtmekanismen bakom den rörliga gränsen tros vara assisterad av diffusion av löst ämne längs korngränsen och generering av den elastiska töjningsenergin av den. Fenomenet är allmänt känt som diffusionsinducerad korngränsmigrering (DIGM) och det tros vara en viktig del av DP Ref. Hillert et al. 1977, Chongmo et al. 1981. För att återskapa DIGM och DP krävs en energetisk koppling mellan molfraktionen och fasfältsvariabeln så att den står för den genererade töjningsenergin under processen. Huvudfokus för denna avhandling kommer att vara att utveckla en fasfältsmodell som redogör för sådan koppling som kommer att förutsäga DIGM i binära system och använda den vidare som ett medium för att modellera DP i (Ti,Zr)C. Modellen för DP skulle kunna användas för att förutsäga och kontrollera dess bildning då dess förekomst är benägen att öka hårdheten hos karbiderna. Därför kan den användas som ett verktyg för att designa legeringar och utveckla bättre alternativ. Alternativen skulle kunna användas för att förhindra DP i karbiderna, vilket skulle kunna göras genom att använda olika metallersättningar som kommer att föredra SD framför DP eller vice versa.

Tungsten carbide-based composites are, in many cases, the materials of choice in applications requiring high wear resistance. In the present research work, the mechanical characterization of the WC-Co and WC-AISI 304 composites was carried out, with evaluation of the hardness and fracture toughness and tribological characterization of the composites that included the study of friction and wear rate coefficient through unlubricated sliding tests according to the Pin-on-Disc test method. It was possible to correlate the effect of the different binding phases on the mechanical and tribological properties of WC-based composites, and it can be concluded that the system composed by the tribological pair WC-AISI304/100Cr6 was the one that showed the lowest coefficient of friction while the tribological pair WC-Co/Al2O3 was the one that showed the lowest wear rate coefficient.

Laser-based additive manufacturing of cemented carbides (WC-Co) remains challenging due to crack forming and residual porosity. Reduction of temperature gradients by high preheating temperatures and successive thermal treatments are starting points for improving the quality of additively manufactured components. Thermal post-treatment is beneficial for the final densification and homogenization of the microstructure. In this study, hot isostatic pressing (HIP) and sinter-HIP are used for thermal post-treatment of additively manufactured parts of WC-12Co. Both methods use elevated temperatures and pressures for densification. Densification during the sinter-HIP process is achieved by liquid phase sintering, while in the HIP process, compaction is expected by plastic deformation of the material. The effect of these both methods for post-treatment on microstructure and fracture strength is investigated in this study. Subsequently, tungsten carbide grain size, as well as the composition of the binder phase, are related to these results.

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.

Previous studies on Laser Powder Bed Fusion of tungsten carbide-cobalt (WC-Co) revealed several defects in the laser molten microstructures. To analyze the defect formation mechanisms and the fundamental impact of laser energy input on phase development and microstructure of WC- Co, single-pulse and single-track analogy experiments are conducted. Conventional WC-Co is used as substrate. Variations in cobalt content and processing conditions are investigated. It is found that a single laser exposure can be enough to induce decomposition of microstructure, WC grain growth, formation of non-equilibrium phases and thermal cracking. Based on the results, defect formation mechanisms and countermeasures are discussed.

Hardmetals are widely used as cutting, machining, and drilling tools for rocks due to their excellent properties of hardness, fracture toughness, and wear resistance over a wide temperature range. This study proposed to evaluate the fracture toughness of WC–10% Co carbide, sintered via spark plasma sintering—SPS, through the Vickers indentation measures, using a modification of the Palmqvist test, which is widely used to assess the toughness of cemented carbides, and to compare this result with the results of six different conventional models: Shetty, Niihara, Laugier, ISO 28079, Hanyaloglu, and Lankford. The model to assess the toughness proposed in this study showed similarity with the Palmqvist test. However, there were considerable differences in the KIC values for the different models, such as 13.36 MPa·m1/2 and 4.44 MPa·m1/2 for the same application load. Comparing the values of the conventional fracture toughness and proposed fracture toughness, the greatest difference between the fracture toughness values was found in the Lankford equation, which varied by 14.74%. The Hanyaloglu equation showed a smaller difference between the fracture toughness values, with a greater variation of 3.61% and lower variation of 1.54%. Adequate results of hardness were obtained, with a maximum of 20.93 ± 0.25 GPa, minimum of 15.76 ± 0.63 GPa, and densification of 99.14 ± 0.47 g/cm3.

DNN (Deep Neural Network) is one kind of method for artificial intelligence, which has been applied in various fields including the exploration of material properties. In the present work, DNN, in combination with the 10-fold cross-validation, is applied to evaluate and predict the thermal conductivities for two-phase WC-M (M = Ag, Co) cemented carbides. Multi-layer DNNs were established by learning the measured thermal conductivities for the WC-Ag and WC-Co systems. It is observed that there are local-minimum regions for the loss functions during training and testing the DNNs, and the presently utilized Adam optimizer is valid for breaking the local-minimum regions. The good agreements between the DNN-evaluated thermal conductivities and the measured ones manifest that the DNNs were well trained and tested. Moreover, another 1000 input data points were randomly generated for the established DNNs to predict the thermal conductivities for WC-Ag and WC-Co systems, respectively. Compared with the thermal conductivities predicted by the previously developed physical model, the presently established DNNs show similarly robust predicting ability. Concerning the efficiency, it is demonstrated in the present work that machine learning is promising to explore the material properties, especially in the high-dimensional parameter space, more efficiently than previous models, and thus can considerably contribute to the corresponding material design with less time consumption and costs.

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.

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 fraction of interfacial layers strongly depend on the presence of bulk (V,W)Cx precipitates and V activity in the binder phase. In-situ ND experiments during aging of (Ti,Zr)C-based systems provide time-resolved insights into the kinetics and structural evolution during phase separation at 1600 oC for 10 h. The results reveal that the decomposition of (Ti,Zr)C into TiC- and ZrC-rich phases can be significantly retarded by minor HfC or NbC additions. During decomposition, in line with the nucleation and growth process, no change is observed in the lattice parameter of ZrC-rich phase. In contrast, the lattice parameter of TiC-rich phase reduces with decomposition, resulting from TiC enrichment, i.e. it reaches equilibrium composition in the course of time. Furthermore, a novel multi-principal element carbide system (Ti,Zr,Hf,W)C with exceptional hardness is designed. Although the system has a miscibility gap, only minor decomposition is observed after 100 h aging at 1350 oC, where the formation of (Ti,W)C- and (Zr,Hf)C-rich decomposition products and WC precipitates occur. Such hindered decomposition enables the carbide system to preserve its high hardness. In summary, by using neutron scattering techniques, this thesis contributes to a better understanding of nano- and microstructural evolution in hard metals and related systems during their processing at elevated temperatures. The thesis and appended papers also guide readers regarding the planning, e.g. sample preparation and sample environment selection, and data analysis of neutron scattering experiments. The thesis can thus serve as a starting point for the more widespread utilization of neutron scattering techniques by the hard metal industry. 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 sintringstemperaturer undersöks ytterligare genom in-situ SANS upp till 1500 °C. Resultaten visar att storleken och volymsfraktionen hos gränsskikten starkt beror på närvaron av bulk (V,W)Cx-utskiljningar och V-aktivitet i bindefasen. In-situ ND-experiment under åldring av (Ti,Zr)C-baserade system ger tidsupplösta insikter i kinetiken och den strukturella utvecklingen under fasseparation vid 1600 °C under 10 timmar. Resultaten visar att sönderfallet av (Ti,Zr)C till TiC-och ZrC-rika faser kan fördröjas avsevärt genom små mängder av HfC eller NbC-tillsatser. Under sönderdelning observerades ingen förändring i gitterparametern för ZrC-rik fas. Däremot minskar gitterparametern i TiC-rik fas under sönderfallet, vilket är ett resultat av TiC-anrikning och liknar spinodalt sönderfall. Dessutom har en ny karbid i systemet (Ti,Zr,Hf,W)C designats och den har exceptionell hårdhet. Även om systemet har en blandningslucka så sker endast smärre sönderfall efter 100 timmars åldring vid 1350 °C genom bildning av (Ti,W)C-och (Zr,Hf)C-rika produkter och WC-utskiljningar. En sådan långsam sönderfallskinetik gör att karbiden bibehåller sin höga hårdhet. Sammanfattningsvis, genom att använda neutronspridningstekniker bidrar denna avhandling till en bättre förståelse av nano- och mikrostrukturutveckling i hårdmetaller och relaterade system under olika industriellt relevanta processer vid hög temperatur. Avhandlingen och bifogade artiklar vägleder även läsarna angående förberedelser, t.ex. prov och provmiljö, och dataanalys efter neutronspridningsexperiment. Avhandlingen kan därmed vara en utgångspunkt och stimulera vidare användning av neutronspridningstekniker inom hårdmetallindustrin. 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 [0001]/[110] interface combinations based on the interfacial energy.

Článek se zabývá hlubokým kryogenním zpracováním (DCT) slinutých karbidů (SK) typu WC-Co. K experimentu byly vybrány čtyři sort SK, které se lišily hrubostí zrn WC a objemem pojiva Co. U části vzorků bylo provedeno jejich DCT zpracování při teplotě -186 0C v prostředí kapalného dusíku. Druhá část vzorků byla popuštěna při teplotě 450 0C. U zpracovaných vzorků byla následně provedena analýza změn v jejich korozní odolnosti v prostředí uměle připravené důlní vody potenciodynamickou zkouškou. Změny v mikrostruktuře analyzovaných vzorků byly hodnoceny s použitím RTG difrakční anlýzy. Výsledky experiment ukázaly, že vzorky po DCT procesu mají vyšší korozní odolnost vůči vzorkům bez tohoto zpracování a vzorkům popuštěným. RTG difrakční analýza prokázala, že při DCT zpracování vzorků došlo ke změně podílu fází ε-Co a α-Co. Podíl takto přeměněné faze závisel na hrubosti zrn karbidické faze a podílu pojiva Co. Deep cryogenic treatment (DCT) of WC-Co cemented carbides (CC) was experimentally explored. Four types of cemented carbides were studied. They had different WC grain sizes and the volume fractions of the cobalt binder. Some specimens were deep-cryogenic-treated (DCT) at -186°C in dry vapour of liquid nitrogen. Another group of specimens was tempered at 450°C. The corrosion resistance of treated specimens was then determined by potentiodynamic testing in artificial mine water. Microstructural changes were characterized with the aid of X-ray diffraction analysis. DCT-treated specimens showed a higher corrosion resistance than the untreated ones and than those which were only tempered. X-ray diffraction analysis revealed that DCT changed the ratio of ε-Co and α-Co phases. The extent of these transformations was dictated by the carbide phase grain size and by the volume fraction of cobalt.

The focus of this paper is on examining the mechanical behavior of spark plasma sintered WC-Co based composites doped with Cr3C2, TaC-NbC, TiC, and VC, as well as defining some parameters characterizing deformation and fracture processes during hardness measurement. The calculated microhardness of WC-Co cemented carbides for all the studied compositions is found to be higher than the results obtained during hardness testing. Therefore, the ratio of the experimental and calculated values of microhardness is shown to be an approximate indication of WC-Co cemented carbide sensitivity to damage processes during indentation. Some parameters characterizing the microstructure–microhardness relationship are defined, and the nanomechanical properties of WC-Co cemented carbide phases are examined in order to separate the deformation and fracture processes during the indentation process. Strain gradient linear function parameters are calculated for 10-cycle nanoindentation. It was found that the nanoindentation curve after 10 cycles shows anomalous behavior of the WC grains, which indicates their fracture processes.

In recent years, coated cemented carbides have often been the first choice for a wide variety of tool inserts and applications. Its success as a cutting tool material arises from the unique combination of wear resistance and toughness, and its ability to be formed into complex shapes. The structure obtained by sintering nanoparticle powders provides a significant improvement in product properties, such as higher cutting speeds, lower tool tolerances, and longer service life. In this study, a multi-layered gradient coating, deposited on nanostructured cemented carbides by plasma-assisted chemical vapor deposition (PACVD) was investigated with emphasis on its wear and exploitation properties. TiBN coating was deposited on nanostructured cemented carbide samples with the addition of 5 wt% Co, 10 wt% Co and 15 wt% Co. The samples were consolidated by one cycle hot isostatic pressing (HIP) technique. Complex architecture built of TiN and TiB2 gradient multilayer sequence block was deposited on each type of substrate. Wear resistance of the obtained samples was determined by erosion wear testing and dry sliding wear testing (ball-on-flat test). The friction coefficients of ~0.22 obtained for coated samples by the ball-on-flat test show a decrease in friction when compared to uncoated samples values of ~0.32. The absence of coating rupture was confirmed by wear track depth measurements showing a wear trace depth of ~1.2 μm. Exploitation properties i.e., tool life determination of samples was obtained using single-point turning tool test and compared to commercial cutting tool insert type K10 tested under the same conditions. All the conducted tests show excellent wear and exploitation properties of the newly developed TiBN coating under chosen conditions, including cutting speed, vc = 200 m/min, depth of cut, ap = 1 mm, and feed, fn = 0.2 mm. Coated WC-Co samples with 15 wt% Co, having withstood 15 min of machining with flank wear trace size less than 0.3 mm, suggest significant improvement when compared to trace size of 0.56 mm obtained for K10 commercial cutting insert.

International audience; Cemented carbides are used in the cutting tools industry thanks to their exceptional mechanical properties. Manufactured by the powder metallurgy route, they are made of a hard WC phase with a ductile metallic binder, most commonly Co. Due to the lower availability of Co and its classification as carcenogenic material by the REACH European Regulation, new metallic binders have to be considered: Fe and Ni binders are investigated in this work. Because Co is the most common binder used in the hard metal industry for decades, there is still a lack of knowledge regarding the specific effect of alternative binders on shrinkage and microstructure evolution of cemented carbides. The purpose of this work is to understand the effect of binder nature specifically, comparing classic Co binder used in the industry to pure Fe and Ni binder including the influence of carbon content. Shrinkage behaviour and microstructure evolution of WC-M alloys (M=Co, Ni, Fe) are studied from dilatometry experiments as well as qualitative and quantitative microstructural characterisations. Solid state sintering is delayed to higher temperature for WC-Fe in comparison to WC-Co and WC-Ni alloys. Densification mechanisms are discussed in relation with dilatometry results, microstructural analyses, DFT calculations and a theoretical kinetic model from the literature.

The study focuses on microstructural evolution in a WC-Co powder mixture during Selective Laser Melting (SLM) and hot isostatic pressing (HIP) processing. This powder mixture contained a 13 &plusmn, 0.6% weight fraction of Co binder and WC particles of mean size of 3.0 &plusmn, 1.9 &mu, m. SLM of the mixture produced samples of various densities, depending on the volumetric energy density (VED) applied. High VED levels led to densities of up to 88%. The aspects affected by changes in VED included the pore density as well as the resulting types of phases and the size of WC phase particles. At high VED, the material began to develop cracks due to embrittlement. This had multiple causes: coarsening of &alpha, phase (WC), evaporation of &beta, phase (Co binder), and precipitation of &eta, phase. At low VED levels, pores formed, typically of nonsymmetric shapes, with sizes larger than 500 &mu, m. Subsequent HIP processing led to an increased density, up to 96% of solid material. Contributions to this increased density were provided by structure transformations, namely, coarsening of &alpha, phase by up to 1300% when compared to the powder grain size, and formation of &eta, phase. The results provided a basis for steering further research to explore to a greater depth the SLM and HIP processing of selected WC-Co powder mixtures with as yet unused ranges of process parameters.

The combined use of focused ion beam (FIB) milling and field-emission scanning electron microscopy inspection (FESEM) is a unique and successful approach for assessment of near-surface phenomena at specific and selected locations. In this study, a FIB/FESEM dual-beam platform was implemented to docment and analyze the wear micromechanisms on a laser-surface textured (LST) hardmetal (HM) tool. In particular, changes in surface and microstructural integrity of the laser-sculptured pyramids (effective cutting microfeatures) were characterized after testing the LST-HM tool against a steel workpiece in a workbench designed to simulate an external honing process. It was demonstrated that: (1) laser-surface texturing does not degrade the intrinsic surface integrity and tool effectiveness of HM pyramids; and (2) there exists a correlation between the wear and loading of shaped pyramids at the local level. Hence, the enhanced performance of the laser-textured tool should consider the pyramid geometry aspects rather than the microstructure assemblage of the HM grade used, at least for attempted abrasive applications.

International audience; Cemented tungsten carbides with Co, Ni or Fe binders were studied by transmission electron microscopy. Particular attention was paid to phase and grain boundaries. A striking feature is the high frequency of coherent carbide/binder interfaces with Fe. The Fe rich binder adopts an epitaxy orientation relationship with prismatic facets of WC, with a parametric misfit of about 1.5%. A special orientation relationship with basal facets of WC grains is sometimes observed with Ni binder, as already noticed for Co. It is associated with a parametric misfit of about 15%. Binder segregation in WC grain boundaries was studied taking into account the effect of carbon content in the alloys. Whatever the binder, no influence of the carbon content could be pointed out. The analyses performed in random grain boundaries in WC-Co alloys agree with the literature value of 0.5 monolayer of segregated Co while slightly larger values are obtained for Ni and Fe binder. ∑=2 special grain boundaries were studied in WC-Co and WC-Ni alloys and no segregation was detected. The higher grain boundary segregation as well as the occurrence of coherent interfaces should influence the mechanical properties of WC-Fe alloys.

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.

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&rsquo, 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 &deg, 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.

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.

Cemented carbide tools are often used for milling operations that cause high thermal and mechanical process loads, e.g. machining processes for titanium alloys. However, the disposal of those tools after one life cycle would significantly reduce their resource efficiency. Therefore, regrinding operations are crucial in order to recycle worn tools and ensure an economical as well as resource efficient manufacturing process. The main challenges during regrinding are the precise quantification of present defects and the subsequent determination of the grinding allowance. As it is, a worker performs both tasks using his individual estimations. Consequently, the estimated grinding allowance is often too low or too high. This either decreases the lifetime of the reground tools due to remaining defects or reduces the resource efficiency since more material than necessary is removed. This paper investigates the determination of the grinding allowance and the environmental impact of regrinding operations on the life cycle of the investigated tools. It is shown that about 12.5% percent of the worn tools are being unnecessarily disposed of. Furthermore, the resource efficiency of tools with small breakouts might be increased by 20% if the recommended allowance strategy is utilized. The tool wear of the grinding tools is also taken into consideration in order to further increase the resource efficiency of the whole life cycle, including milling tool and grinding wheel. The results show that small grain sizes and low grain concentrations are not suitable for efficient regrinding processes since higher wear and consequently higher geometrical inaccuracies of the reground tools occur.

A study was carried out to investigate the influence of the initial powder features on the microstructure, the phase composition, and on the mechanical properties of WC-12%Co samples produced by binder jetting and densified by sintering in vacuum at 1400 °C and by sinter-HIPing. The initial powder consisted of a mixture of fine-grained and coarse-grained WC-based particles, and W2C-based ones. The density of the printed samples was 97.4% and 99.3% after sintering and sinter-HIPing, respectively. Layer-oriented porosity was observed only in sintered samples. The microstructure of the samples consisted of a mixture of fine and coarse WC grains, which can be the result of the coalescence of grains from anomalous coarse grains in the powder particles. Vickers hardness and transverse rupture strength of sinter-HIPed samples are 1205 HV and 2257 MPa, respectively, which is coherent with the microstructural analysis and close to coarse-grained commercial products.

We present a new method for retarding the oxidation rate of hardmetals. By diffusion impregnating a WC-FeCr hardmetal with silicon, we manufacture two-layered silicide coatings consisting of an FeSi x outer crust and WSi 2 beneath. The structure results from a preferential reaction between silicon and the metallic binder. The FeSi x outer layer is crucial to providing oxidation resistance as when exposed to oxygen it passivates, forming a protective SiO 2 surface film – while simultaneously preventing exposure of the underlying WSi 2 , which is known to oxidise in an active manner. Our analysis shows the coating method is applicable to various hardmetals structures.

In this research, the wear behavior of commercial grades of WC-10wt%Co (H10F), WC-40vol%Co and WC-40vol%FeAl-B composites with different amounts of boron from zero to 1000 ppm has been investigated by the pin on disk testmethod at high temperature. The wear tests were done under load of 40 N, a distance of 100 m and at ambient temperature, 200 ̊C and 300 ̊C. Wear surfaces were examined by scanning electron microscopy. The results showed that the wear resistance of all composites decreased with increasing temperature. The boron free WC-40vol%FeAl composite showed the lowest wear resistance at all ranges of temperature. In the presence of boron up to 500 ppm in iron-aluminide matrix, the high temperature wear resistance of these composites improves and the wear mechanisms changes from particle pullout into abrasive state. The toughness enhancement of these composites and plasticity enhancement of iron aluminide in the presence of boron, leads to better link of the interface of FeAl matrix and tungsten carbide particles, and thus increases the wear resistance of these composites. WC-40vol% FeAl-500ppmB composite has a higher wear resistance at high temperature than WC-40vol% Co and commercial WC-10wt% Co. &nbsp

Níže uvedený článek se zabývá zpracováním různých typů práškových směsí WC-Co technologií SLM. Použité práškové směsi se lišily svojí morfologií částic prášku, tj. Lišily se tvarem, velikostí a chemickým složením jednotlivých částic prášku. Celkem byly pro experiment použity dva různé typy práškových směsí WC-Co. Studium bylo zaměřeno na hodnocení vlivu aplikované energie na vlastnosti vyrobeného prototypového vzorku. Z toho důvodu byly prototypové vzorky vyrobeny při stejné hodnotě aplikované hustoty energie Ev= 238 J/mm3. U vzorků byla po jejich přípravě provedena metalografická analýza. Tato analýza byla provedena za použití světelného a řádkovacího elektronového mikroskopu. Metalografická analýza byla doplněna o analýzu fázového složení prototypových vzorků a analýzu změn v jejich chemickém složení a korozní odolnosti. Díky provedeným experimentům bylo potom možné porovnat rozdíly ve vlastnostech protypových vzorků a to zejména z hlediska jejich poréznosti, strukturních změn, změn v chemickém složení a složení fázovém a korozní odolnosti. Na základě získaných dat bylo možné například uvést, že u všech vzorků došlo díky difúzi prvků, zejména pak uhlíku, k vytvoření fáze éta, která je brána jako fáze nežádoucí. Její objemové množství se ovšem lišilo v závislosti na tom, jaký typ prášku a za jakých podmínek se zpracovával. Její nejmenší množství bylo zaznamenáno u vzorků vyrobených z práškové směsi s volnou vazbou mezi částicemi pojiva a zrny karbidu wolframu. The paper deals with the influence of different types of WC-Co powder mixtures processed by SLM technology on the final properties of the prototype build.The powder mixtures used differed in the morphology of the powder particles, i.e. the shape, size and chemical composition of the individual powder particles. In total, two different types of WC-Co powder mixtures were used for the experiment. The study was focused on the evaluation of the effect of these powders and other parameters of SLM technology (applied energy) on the resulting properties of the prototype sample.The samples were subjected to metallographic analysis after their preparation. This analysis was performed using metallographic and scanning electron microscopes. The metallographic analysis was supplemented by analyzing the phase composition of the prototype samples and the changes in their chemical composition. The experiments enabled us to compare the differences in the properties of the prototype samples, especially in terms of their porosity, structural changes, changes in chemical and phase composition. The information obtained in relation to the parameters of the technology and the powders provided us with interesting data. The diffusion of the elements, especially carbon, meant the eta phase was formed in all of the samples, which is considered to be an undesirable phase in cemented carbides. However, its volume varied depending on the type of powder and the processing conditions. The smallest amount was recorded for samples made from a powder mixture with a free bond between the binder particles and tungsten carbide grains.

Příspěvek se zabývá možností chemicko-tepelného zpracování slinutých karbidů (SK) boridováním. Pro experimentální program byly zvoleny 3 různé sorty SK s velice jemnou frakcí zrn karbidu wolframu (WC). Struktura těchto SK se lišila chemickým složením pojiva. Byly vybrány dvě sorty SK, u kterých bylo pojivo tvořeno čistými kovy a to kobaltem a niklem. U třetí sorty SK bylo zvoleno komplexní pojivo na bázi Fe-Co-Cr. Objem pojiva byl pro všechny zvolené sorty SK shodný a to 8 hm. %. Velikost zrna WC se pohybovala mezi 0,5-0,8 µm. Z vybraných sort SK byly vytvořeny vzorky, z nichž část podstoupila proces boridování a to v několika různých režimech. Cílem provedeného experimentu bylo určit, jakým způsobem ovlivňuje proces boridování konečné vlastnosti SK a jejich strukturu. K hodnocení strukturních změn byly použity techniky RTG difrakce a techniky světelné a elektronové mikroskopie. K hodnocení změn v mechanických vlastnostech a odolnosti proti opotřebení byly použito měření tvrdosti a zkouška Ball on Disk. This paper explores the thermochemical treatment of cemented carbides (CC), specifically the boriding process. Six different types of CCs with different size of tungsten carbide (TC) grains were chosen as experimental materials. They contained binders of different chemical compositions. In five CCs, the binders were pure metals: cobalt (four of them) and nickel (one of them). In the six one, the binder was a complex Ni-Co-Cr-based alloy. Samples of the different types of CCs were prepared by grinding and polishing and then half of them underwent boriding process. The experiment aimed to find how boriding affects the final properties of CCs and their structure. Microstructural changes in the materials were examined using X-ray diffraction and optical and electron microscopy. Changes in mechanical properties and wear resistance were evaluated using hardness testing and the Ball on Disk test. The experimental results, for example, shown that CC with nickel binder had lowest wear resistance from all tested sorts of CC.

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.

Předložená studie se zabývá vývojem struktury práškové směsi WC-Co a to při jejím postupném zpracování SLM a HIP technologií. Použitá prášková směs obsahovala 13±0.6% hmotnostní podíl pojiva Co a WC frakci o průměrné velikosti zrna(3.0±1.9) μm.Jejím zpracováním SLM technologií došlo, v důsledku aplikace různé hustoty energie (VED), k vývoji různého stupně hustoty vytvářených vzorků. Při vysokých hodnotách VED bylo dosaženo hustoty až 88 %. Aplikovaná hodnota VED ovlivnila kromě hustoty pórů, které se ve struktuře vzorků vytvářely, typy strukturních fází a hrubost WC fáze. Při vysokých hodnotách VED se ve struktuře vzorků začaly utvářet trhliny, které vznikaly v důsledku zkřehnutí struktury vzorků a to z několika důvodů, mezi které patřilo hrubnutí α-fáze (WC), vypařování β-fáze (pojiva Co) a precipitace η-fáze. Při nízkých hodnotách VED byla oproti tomu struktura pórů tvořena převážně tvarově nesymetrickými póry, i o velikosti vyšší jak 500 μm. Následným zpracováním vybraných vzorků technologií HIP bylo dosaženo zvýšení jejich hustoty až na hodnotu 96 % kompaktního materiálu. Na tomto zvýšení hustoty se podílely strukturní přeměny zejména pak opětovné hrubnutí α-fáze až o 1300 % oproti původní velikosti zrna práškové směsi a vývoj η-fáze ve struktuře analyzovaných vzorků. Na základě získaných výsledků pak bylo možné rozhodnout o dalším směřování experimentálního programu, který se do větší hloubky bude zabývat zpracováním vybraných práškových směsí WC-Co technologiemi SLM a HIP za doposud nerealizovaných parametrů jejich zpracování. The study focuses on microstructural evolution in a WC-Co powder mixture during Selective Laser Melting (SLM) and hot isostatic pressing (HIP) processing. This powder mixture contained a 13 plus/minus 0.6 % weight fraction of Co binder and WC particles of mean size of 3.0 plus/minus 1.9 μm. SLM of the mixture produced samples of various densities, depending on the volumetric energy density (VED) applied. High VED levels led to densities of up to 88%. The aspects affected by changes in VED included the pore density as well as the resulting types of phases and the size of WC phase particles. At high VED, the material began to develop cracks due to embrittlement. This had multiple causes: coarsening of a-phase (WC), evaporation of b-phase (Co binder), and precipitation of h-phase. At low VED levels, pores formed, typically of nonsymmetric shapes, with sizes larger than 500 μm. Subsequent HIP processing led to an increased density, up to 96 % of solid material. Contributions to this increased density were provided by structure transformations, namely, coarsening of a-phase by up to 1300 % when compared to the powder grain size, and formation of h-phase. The results provided a basis for steering further research to explore to a greater depth the SLM and HIP processing of selected WC-Co powder mixtures with as yet unused ranges of process parameters.

WC-Co cemented carbides (hardmetals) represent the backbone materials for the tooling industry. In order to achieve particular tool geometries, diamond wheel grinding is a well-established method for machining hardmetals. Grinding-induced damage has been proven to strongly affect the performance and reliability of the machined tools. Assessment of grinding-mechanisms and induced surface integrity changes has usually been limited to monolithic ceramics, and it is particularly done on the basis of post-failure fractographic examination. In this work, characterization of grinding-induced damage of a WC-Co grade has been conducted by means of focused ion beam (FIB) tomography. The study includes a 3D description of the damage scenario, based on a reconstruction from successive parallel slices. Our results show that grinding induces a 200-400 nm thick surface layer containing fragmented WC grains and smeared Co phase morphology. A highly anisotropic subsurface microcrack network is generated. The discerned microcracks follow different microstructural paths: running through the binder, close to WC/Co interfaces or transgranular within the carbide phase. Very interesting, completely or near- lateral cracks (parallel to the ground surface) are found to be the predominant damage feature, whereas only few completely or near- orthogonal (perpendicular to the ground surface) cracks are discerned. Results are discussed in terms of material removal mechanisms during grinding of cemented carbides and surface integrity effects on the mechanical performance of hardmetal tools under service conditions.

Cemented carbides are composites made of a hard refractory ceramic phase and a ductile binder, most commonly WC and Co, respectively. Since the use of cobalt in the hard metal industry is questioned by the new European regulation on chemicals, extensive research has been done to develop new grades based on a Co-Ni-Fe binder. With similar mechanical, physical properties and affinity to C and W, nickel and iron are the best candidates for an efficient binder in cemented carbides. As mechanical properties are strongly dependent on the materials microstructure, and especially on the WC grain size, understanding the effect of the binder on the final microstructure is crucial. In this work, the carbide grain growth behaviour of WC-M alloys (M = Co, Ni, Fe) with different carbon contents is discussed from qualitative and quantitative microstructural analyses. Whereas grain growth is more or less inhibited in WC-Fe alloys, increasing carbon content promotes grain growth in WC-Co and WC-Ni alloys, with a slight abnormal grain growth in case of Ni binder. Different mechanisms for grain growth are discussed, in relation with the observed morphology of WC grains after sintering.