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We investigated the effect of barothermal treatment at a pressure of 8 GPa and temperatures of 1450–1700°C on the structure and properties of cemented carbides with varying cobalt concentrations. The application of barothermal treatment led to a 30% increase in the grain size of the carbide phase and a decrease in overall porosity. For WC–6Co alloys treated under conditions of solid-phase sintering, an increase in hardness and the stress intensity factor are observed. The barothermal treatment of WC–15Co alloys at temperatures corresponding to the existence of a liquid phase leads to the formation of Co3W3C intermetallic phases. [ABSTRACT FROM AUTHOR]

WC–Co cemented carbides were prepared via an in situ synthesis method, including the carbothermal prereduction of WO3 and Co2O3 to remove all oxygen and a subsequent carbonization‐vacuum sintering process. The experimental results revealed that as the prereduction temperature increased from 1000 to 1200°C, the grain sizes of WC in WC–6Co and WC–12Co cemented carbides increased from.91 to 1.09 and.97 to 1.19 μm, respectively. Further, the fracture toughness of the sintered WC–6Co and WC–12Co cemented carbides increased from 9.97 to 10.83 and 11.11 to 18.30 MPa m1/2, respectively. In contrast, the hardness of the WC–6Co and WC–12Co cemented carbides decreased from 1477 to 1368 and 1351 to 1184 HV30, respectively. For a given prereduction temperature, an increase in Co content can improve the fracture toughness while lowering the hardness. In addition, an increase in the prereduction temperature or Co content led to an increase in the grain size of WC, which resulted in a transgranular fracture as the dominant mode. [ABSTRACT FROM AUTHOR]

WC–Fe–Ni‐cemented carbides are prepared by hot oscillating pressing (HOP) and hot pressing (HP). Compared with the sample prepared by applying HP, the sample prepared by HOP shows higher density, lower carbide contiguity, more uniform distribution of binder phase, and finer WC grains. The average grain size of the HOP sample is 0.54 μm, where that of the HP sample is 0.67 μm. Moreover, the content of W in the binder phase is higher in the HOP sample than in the HP sample. The HOP sample exhibits a hardness of 2080 MPa and a fracture toughness of 15.95 MPa.m1/2, which are not only higher than those of the HP sample, but also higher than those of the WC–10Co alloys reported previously. The improvement in the mechanical properties is likely due to that the oscillatory pressure enhanced the flow of the liquid binder phase as well as influenced dissolution and re‐precipitation during densification process. Herein, it is indicated that HOP is an effective technique for the preparation of cemented carbides having high hardness and high toughness. [ABSTRACT FROM AUTHOR]

For cemented carbides, also known as hardmetals, fracture toughness has always been viewed as one of the key properties, which resulted in large amount of research in the subject. This study presents fracture toughness results for 30 cemented carbide grades, covering wide range of microstructures and associated properties. Toughness data was generated at room temperature by three-point bend testing of chevron notched samples. In addition to relatively well studied influences of cobalt content and carbides grain size on fracture toughness, current research also examines impacts of cubic carbides content and alloying elements on material toughness. In this work, traditional "hardness - toughness" diagram is complemented by "coercivity - toughness", which is shown to be more appropriate for illustration of the detrimental effect that cubic carbides have on fracture toughness. The results presented here also indicate that alloying of binder with Cr or Ru does not have any noticeable effect on room temperature toughness and presence of eta-phase in the microstructure is not necessarily harmful for toughness. In addition, this research illustrates a correlation between fracture toughness and thermal conductivity of cemented carbides. Most importantly, by utilising broad experimental data and regression analysis, an attempt is made to formulate a set of empirical equations that would allow fracture toughness estimate from readily available or easily measurable material parameters. It is shown that fracture toughness of cemented carbides can be predicted with good accuracy from coercivity and cubic carbides content. In addition, regression equations for estimate of hardness and the average carbides grain size are proposed. • Fracture toughness of cemented carbides with wide range of microstructures. • Correlations of toughness with hardness, coercivity and thermal conductivity. • Influence of WC grain size, binder content and cubic carbides fraction on toughness. • Effect of Cr, Ru and eta-phase in the binder on fracture toughness of hardmetals. • Simple prediction of K 1C and HV with empirical equations using magnetic properties. [ABSTRACT FROM AUTHOR]

The WC-10Co cemented carbides containing (ZrHfNbTaTiMo)C high-entropy carbide with satisfactory comprehensive mechanical properties were successfully manufactured by conventional vacuum sintering. The influences of (ZrHfNbTaTiMo)C contents (0, 0.5, 1, 5, 10 wt.%) on the densification degree, microstructure, grain size and mechanical properties were investigated. The results showed that the addition of (ZrHfNbTaTiMo)C deteriorated the wettability between Co and WC, leading to a decline in relative density. (ZrHfNbTaTiMo)C inhibited the growth of WC grains, and the average grain size of WC continued to decrease with the increase of (ZrHfNbTaTiMo)C content. After adding (ZrHfNbTaTiMo)C, the hardness and toughness rose first and then descended. When the content of (ZrHfNbTaTiMo)C was 1 wt.%, the hardness and toughness reached the maximum value of 16.77 GPa and 10.45 MPa·m1/2, respectively. Moreover, the structure was a dual-grain structure, with many high-aspect-ratio rectangular grains in the sintered samples added by 0.5 wt.% and 1 wt.% (ZrHfNbTaTiMo)C. This special structure not only enhanced the hardness, but also compensated the loss of toughness. After doping 0.5 wt.% CeO2, the hardness decreased slightly, while the toughness increased to 12.42%. [ABSTRACT FROM AUTHOR]

Here, the effects of Ru and ball-milling on the mechanical properties of WC–10Co-cemented carbide were investigated using systematic characterisation and microstructure analysis. It was found that with an increase in the Ru content, the WC grain morphology and grain size did not change; however, the values of density and coercivity, Co magnetism, hardness, and fracture toughness of cemented carbide were changed. When the Ru content was 4%, compared with the alloy without Ru, the toughness increased from 16.8 to 24.2 (MPa. m1/2) and the hardness increased from 1290 to 1330 (HV30). Meanwhile, the analysis of the mixing process shows that the optimal ball-milling time is determined by the performance combination of the obtained alloy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

WC-10 wt% Co cemented carbides containing various amounts (0–4 wt%) of SiC nanoparticles were fabricated by vacuum sintering. The influence of SiC nanoparticles on microstructure, mechanical behavior, and dry sling wear resistance of the produced cemented carbides was explored. Results showed that SiC addition resulted in larger WC grains, thus lowering the hardness. Despite the hardness reduction, the wear resistance increased with increasing SiC content. The specific wear rate of the WC-10Co sample was 12.33 × 10−5 mm3/Nm that decreased to 1.86 × 10−5 mm3/Nm with 4 wt% nanoparticle addition. The improved wear resistance of nanocomposite samples was explained through the effects of SiC particles on modification of pore distribution, increased fracture toughness, and reduction of coefficient of friction. In the unreinforced WC-10Co cemented carbide, microstructural pores were found to be smaller but more numerous, resulting in extensive WC grain pullout. In addition, scuffing was recognized as the prevalent wear mechanism making friction trace completely unstable. In the nanocomposite samples, however, SiC nanoparticles stabilized and reduced the coefficient of friction. The change in friction condition from sliding to rolling abrasion revealed the microabrasive grooving as the predominant wear mechanism of the nanocomposites with enhanced wear resistance. [ABSTRACT FROM AUTHOR]

New graphite tools were designed and produced to fabricate a semi-finished product from which nine cutting inserts were obtained in one spark plasma sintering process. As a result, WC-5Co cemented carbides were spark plasma sintered and the effect of various sintering parameters such as compacting pressure, heating rate and holding time on the main mechanical properties were investigated. It was shown that WC-5Co cemented carbides spark plasma sintered at 1200°C, 80 MPa, 400°C/min, for 5 min are characterized by the best relation of hardness (1861 ±10 HV30) and fracture toughness (9.30 MPa·m1/2). The microstructure of these materials besides the WC ceramic phase and Co binder phase consists of a synthesized Co3W3C complex phase. Comparison with a commercial WC-6Co cutting insert fabricated by conventional powder metallurgy techniques shows that spark plasma sintering is a very effective technique to produce materials characterized by improved mechanical properties.

In the current work, a nanostructured NiFeCrWMo high entropy alloy (HEA), synthesized by mechanical alloying, was used as the alternative binder phase for substituting Co to fabricate WC–HEA cemented carbides by electron–beam sintering (EBS). The microstructure and mechanical properties of initial powder mixtures and sintered samples were studied using X-ray diffraction analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS), indentation technique and compression tests. NiFeCrWMo HEA does not have direct interaction with WC, but at the boundaries between WC and HEA particles (Ni, Fe, Cr) x W y C z complex carbide is formed as result of reduction processes during sintering. The results show that WC–HEA cemented carbide has better performances than the commercial WC–8Co-cemented carbide prepared by EBS. The NiFeCrWMo HEA binder significantly slows down the growth of WC grains due to the sluggish diffusion effect and the formation of a small amount of complex carbide, and, compared to Co, improves the mechanical properties, provides an excellent combination of microhardness (18.9 ± 0.4 GPa) and fracture toughness (11.4 ± 0.3 MPa m1/2). Therefore, the NiFeCrWMo high entropy alloy can potentially become a binder for WC cemented carbides. • WC grain growth can be considerably inhibited by the NiFeCrWMo high-entropy alloy. • A small amount of (Ni,Fe,Cr) x W y C z carbide formed during electron-beam sintering. • High microhardness of 18.9 GPa and fracture toughness of 11.4 MPa m1/2 are obtained. [ABSTRACT FROM AUTHOR]

Cemented carbides with mesoscopically non-homogeneous properties by design represent a potential to enhance performance in metal cutting and rock drilling. Development of in-homogeneous structured hard materials through an ICME approach requires a thorough understanding of diffusion kinetics during solid and liquid state sintering. In this work, we used thermodynamics and diffusion kinetics modelling tools to predict the microstructure and resulting properties of cemented carbide composites. First, we designed and gradient sintered two (WC-TiCN-Co) cemented carbides with different nitrogen to titanium ratios. Second, we reproduced the experimental results in 2D by means of thermodynamic and kinetic simulations. In the last step we calculated fracture toughness KIC, and Vickers hardness of cemented carbides. The agreement between simulations and experimental results is fair and acceptable.

Abstract The unique combination of hardness, toughness and wear resistance exhibited by WC-Co cemented carbides (hardmetals) has made them a preeminent material choice for extremely demanding applications, such as metal cutting/forming tools or mining bits, in which improved and consistent performance together with high reliability are required. The high fracture toughness values exhibited by hardmetals are mainly due to ductile ligament bridging and crack deflection (intrinsic to carbides). In this work two WC-Co grades obtained by using the electric resistance sintering technique are studied. The relationships between the process parameters (cobalt volume fraction, sintering current and time, die materials, etc.), the microstructural characteristics (porosity, cobalt volume fraction, carbide grain size, binder thickness and carbide contiguity) and mechanical properties (Vickers hardness and fracture toughness) are established and discussed. Also the presence of microstructural anisotropy and residual stresses is studied. The sintering process at 7 kA, 600 ms and 100 MPa, in an alumina die, followed by a treatment of residual stress relief (800 °C, 2 h in high vacuum), allows to obtain WC-Co pellets with the best balance between an homogeneous microstructure and mechanical behaviour. Highlights • Fabrication of WC-Co pellets using electric resistance sintering technique • Presence of microstructural anisotropy and residual stresses is studied. • Relationships between the fracture toughness, process and microstructural parameters • Balance of structural integrity, density and mechanical behaviour are established. [ABSTRACT FROM AUTHOR]

Tantalum carbides (TaXC) interlayers have been synthesized by double glow plasma surface alloying (DG-PSA) method at different temperature for subsequent deposition of diamond coatings. The evolution of the microstructures, phase composition and adhesion of the interlayers dependent on substrate temperature has been discussed. The results show that the layers are composed of TaXC (i.e. Ta2C, TaC) with nanocrystalline microstructure and small amounts of CoTa2. The layer produced at 700∘C is formed of specific flower-shaped rings embedded in smooth structures. As the temperature increases to 800∘C, interacted rings are covered the full surface, and the surface roughness is increased. As the temperature increases further, the rings are replaced by irregular-shaped pits, caused a decreasing surface roughness. Besides the special microstructure with interactional rings and relatively high roughness, the layer prepared at 800∘C possesses higher adhesion, better wear performance and higher hardness than those of other layers. The coating obtained on the interlayer pretreated at 800∘C exhibits the best adhesion. Thus, the TaXC interlayers synthesized at 800∘C are demonstrated as a suitable option for adherent diamond coatings deposited onto WC-Co substrates. [ABSTRACT FROM AUTHOR]

New graphite tools were designed and produced to fabricate a semi-finished product from which nine cutting inserts were obtained in one spark plasma sintering process. As a result, WC-5Co cemented carbides were spark plasma sintered and the effect of various sintering parameters such as compacting pressure, heating rate and holding time on the main mechanical properties were investigated. It was shown that WC-5Co cemented carbides spark plasma sintered at 1200°C, 80 MPa, 400°C/min, for 5 min are characterized by the best relation of hardness (1861 ±10 HV30) and fracture toughness (9.30 MPa·m1/2). The microstructure of these materials besides the WC ceramic phase and Co binder phase consists of a synthesized Co3W3C complex phase. Comparison with a commercial WC-6Co cutting insert fabricated by conventional powder metallurgy techniques shows that spark plasma sintering is a very effective technique to produce materials characterized by improved mechanical properties. [ABSTRACT FROM AUTHOR]

This paper studies the correlation between the microstructure and the mechanical properties at the nanometric length scale of individual WC grains as well as the metallic cobalt binder in cemented carbide systems. The local crystallographic orientation has been determined by electron backscattered diffraction and the microstructural analysis has been performed using field emission scanning electron microscopy. Small-scale hardness and elastic modulus have been assessed by means of high speed massive nanoindentation and subsequent statistical analysis. The attained mechanical property mappings present a clear correlation between local hardness and stiffness with chemical nature for each constitutive phase as well as with the crystallographic orientation for the WC particles. Besides expected findings associated with individual phases, such as clear anisotropy of the ceramic phase (basal plane being harder and stiffer than the prismatic one) and relatively high flow stress for constrained binder, the protocol implemented provides novel information on local mechanical response at interfaces between ceramic particles with different orientations as well as regions within the metallic cobalt binder close to the WC-Co interface. [ABSTRACT FROM AUTHOR]

Different commercial WC-Co hard metals with carbide grain sizes ranging from ultrafine to coarse and Co contents between 4.2 and 25 wt.% have been investigated with regard to their microstructural and mechanical properties. Therefore, novel preparation strategies – including specific etching reactions – and microscopic methods for the microstructural characterization were developed. Two sets of microscopic images were generated suitable for further semi-automatic determination of either the Co volume fraction φ Co or the mean maximum Feret diameter d Fer of the WC grains considering the irregular shape of the grains. Subsequently, the determined microstructural parameters and measured Vickers hardness values were used to develop a novel model calculating the hardness of WC-Co hard metals. The total hardness is mainly determined by the hard carbide whereby its influence is reduced by the soft Co binder phase. The current model is in good agreement with the measured values within almost the whole relevant hardness range of WC-Co hard metals (700 - 2300 HV 10) and do not require any statement of the existence of a carbide skeleton within the material and thus the Co binder mean free path which is essential for hardness models established so far but also hard to determined experimentally. So the current model is a significant simplification and improvement of the prediction of the hardness of WC-Co hard metals by means of microstructural parameters. [ABSTRACT FROM AUTHOR]

The nano-hardness in the alternative 85 Ni- 15 Fe binder phase of WC cemented carbide has been investigated. High-resolution scanning electron microscopy (SEM) imaging was used to measure the projected indentation area and a general pile-up correction, confirmed on selected indents, has been employed using atomic force microscopy (AFM). Focused ion-beam (FIB) cross-sections have been used to investigate the binder morphology below the indentations and the local binder hardness has been associated to the distance to the surrounding WC grains. Generally, decreasing distance to the WC grains leads to increased binder hardness. Furthermore, the nano-hardness for the cemented carbide binder has been corrected for the indentation size effect (ISE) to obtain the corresponding macroscopic hardness. A solid solution strengthening model for multicomponent bulk alloys was used to calculate the expected binder Vickers hardness considering the binder solubilities of W and C. Both the strengthening model and the ISE corrected hardness values, for larger binder regions, are in good agreement indicating that the intrinsic binder phase hardness is similar to that of a bulk metal alloy with similar composition. [ABSTRACT FROM AUTHOR]

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. • Laser produced abrasive-like protrusions were protected by three AlTiN-based PVD coatings. • The coating-substrate systems were assessed by means of indenting and sliding contact testing. • The TiSiN-AlTiN coating achieved the best performance, followed by the TiSiN-AlTiN-CrN coating and AlTiN-CrN coating. [ABSTRACT FROM AUTHOR]

WC-MC/M(C,N)-Co hardmetals with 10 wt% Co were prepared in undoped, as well as in either Cr- or V-doped form. The starting formulations contained 5 wt% TiC or 5% (TiC+TiN), the latter with two different TiC/TiN ratios, and 10 wt% (Ta,Nb)C. For each composition, a low-C grade (Ms ≈ 75%) and a high-C grade (Ms ≈ 88%) was adjusted by C or W addition, to end up with 18 different hardmetal formulations, prepared in an industrial process. Model alloys, MC and M(C,N) phases with a composition reflecting the composition of these phases in the hardmetal were prepared, too. A variety of data was collected: binder phase and hard phase compositions of model alloys by wavelength-dispersive electron-probe microanalysis (WDS-EPMA), liquid phase formation temperatures in model alloys with free C and eta by differential thermal analysis (DTA), respectively, thermal conductivities of MC and M(C,N) phases and hardmetals by laser-flash temperature conductivity and heat capacity measurements up to 950 °C, crystallite-size distribution by electron backscatter diffraction EBSD, hardness HV30, Palmqvist-Shetty fracture toughness KIC, Weibull evaluation of the transverse rupture strength (TRS), oxidation resistance in air as well as milling tests on coated hardmetals with Ti(C,N)/Al2O3 and (Ti,Al)N layers.

PVD coating is a critical technique to improve the wear resistance and cutting performance of softer carbide substrates. The wear performance of the coating is closely related to the carbide substrate grade, coating parameters, and the coating materials. In this study, a unique carbide grade, 91WC-2TiC-3Co-3Ni-1Mo, has been developed specifically for PVD coating. Two different coatings i.e. TiAlN and AlCrN were successfully deposited with cathodic arc evaporation (CAE) technique on this carbide grade. The microstructure analysis shows good bonding between coating and carbide substrate. The comprehensive sliding wear testing, including reciprocating sliding, ball-on-disc, and micro-scratch testing, has been made to these two coatings. AlCrN coating shows consistently lower coefficient of friction (COF) compared with TiAlN coating in both reciprocating sliding test and ball-on-disc test. In addition, AlCrN coating has consistently higher normal critical loads than TiAlN coating during micro-scratch testing, demonstrating better bonding condition between coating and carbide substrate. [ABSTRACT FROM AUTHOR]

Microstructure, hardness, transverse rupture strength, and abrasion resistance of WC-10 wt% Co cemented carbides modified with the addition of different mass fraction of Cr3C2, in the range of 0⁻3 wt%, are studied. The influence of the microstructure, composition and hardness on the mechanical properties and wear resistance is analysed. Considering that the material under investigation can be used as die for the extrusion process of hard ceramic materials, the tribological behaviour was evaluated by performing sliding wear tests in wet conditions using a block-on-ring tribometer. Wear mechanism principally based on binder removal and subsequent fragmentation and microabrasion of the WC grains is proposed. Carbide grain size and bulk hardness can be tuned as function of specific applications by adding different amounts of Cr3C2. In particular, increasing hardness and reducing grain size by the addition of Cr3C2 are demonstrated to considerably enhance the wear performance of these carbides.

Cutter development has drawn a lot of attention for cast iron machining in recent years. In this study, a special cemented carbide of WC–5TiC–0.5VC–8Co (WTVC8) was used for a comprehensive HT250 gray cast iron machining test. Compared with the baseline plain WC–8Co(WC8) carbides, WTVC8 shows significantly higher tool life under the same cutting conditions due to significantly higher hardness and red hardness. The worn flank face observation shows that adhesion wear and oxidation are the main wear mechanisms and there is no apparent chipping/breakage and abrasion wear for both WTVC8 and WC8. Based on Taylor's equation, the accurate tool life models for both WTVC8 and WC8 have been constructed, which shows clearly that cutting speed has the most significant effect on tool life, followed by depth of cut and feed rate. The tool life models can serve as a quantified guidance for cutting performance optimization. [ABSTRACT FROM AUTHOR]

Microstructure and properties of WC–Co cemented carbides from WC powders obtained by the self-propagating high-temperature synthesis (SHS) were examined. The microstructure and properties of a submicron carbide grade with 5% Co made from the near-nano SHS WC powder and a standard submicron grade are similar. Microstructure of a medium-coarse WC–6%Co grade made from the medium-coarse SHS WC powder and its properties are comparable with those of the standard medium-coarse carbide grade for percussive drilling. Results of laboratory performance tests on percussive drilling of the medium-coarse WC–6%Co grade obtained from both the SHS powder and conventional WC powder indicate that their wear-resistance and performance toughness are very similar. [ABSTRACT FROM AUTHOR]

This article presents comparative results of investigations of cutting edges made of nanocrystalline and standard cemented carbides. The cutting edges made of nanocrystalline cemented carbides were sintered by the PPS method at various values of temperature (1320–1560 K) for 500 s in a vacuum of 0.05 Pa and under a load of 60 MPa. The results of investigations showed considerable variation in the structure of the nanocrystalline cemented carbides depending on the applied sintering parameters. The nanocrystalline cemented carbides obtained by the PPS method were characterized by considerably higher hardness than the standard cemented carbides with similar chemical composition. The PPS is a new method of producing sintered materials elaborated at Warsaw University of Technology. [ABSTRACT FROM AUTHOR]

The paper consists of three parts. In the first part, functionally graded cemented carbides comprising hard surface layers with low Co contents are described. Such surface layers form as a result of a tailored sintering technique based on the selective carburization of the near-surface layer of carbide green bodies with original low carbon contents and consequent liquid-phase sintering, which leads to Co drifts from the surface towards the core during sintering. This novel sintering technique allows obtaining Co gradients between the surface layer and the core of carbide articles of up 7 wt.%. As a result of significantly different contraction rates between the near-surface layer and the core of such functionally gradient cemented carbides, high residual compression stresses are created in the carbide near-surface layer. This leads to a dramatically increased combination of both hardness and fracture toughness of the near-surface layer. The presence of the hard and tough surface layers on the novel functionally gradient carbides results in their significantly improved wear-resistance and prolonged tool lifetime in mining applications. In the second part of the paper, functionally graded cemented carbides comprising surface layers with high Co contents are described. They are fabricated by a tailored sintering technique based on the selective de-carburization of the near-surface layer of carbide green bodies with original high carbon contents resulting in Co drifts from the core towards the surface during the consequent stage of liquid-phase sintering. Such functionally graded cemented carbides are successfully employed as substrates for poly-crystalline diamond (PCD) layers. In the third part of the paper, a mechanism of formation of thin Co films on the surface of carbide articles during sintering, which is designated in literature as “Co capping”, is briefly described. On the basis of understanding the mechanism of the Co capping phenomenon, an industrial technology for obtaining such thin Co films on the surface of carbide articles during sintering was developed. The wettability of non-ground carbide articles by braze alloys is dramatically improved by use of the thin Co films, resulting in better quality of various brazed wear parts and tools. [ABSTRACT FROM AUTHOR]

For conventional structural and tool materials, in particular WC–Co cemented carbides, hardness and wear-resistance can usually be increased only at the expense of toughness and strength. For the first time we have achieved a dramatically increased combination of hardness, wear-resistance, fracture toughness and strength as a result of precipitation of extremely fine nanoparticles in the cobalt binder of cemented carbides. These nanoparticles are ∼3nm in size, coherent with the Co matrix and consist of a metastable phase. [ABSTRACT FROM AUTHOR]

Highlights: [•] The ultrafine WC–(micron WC–Co) cemented carbides were fabricated. [•] The addition of micron-sized WC particles can generate the deflection of crack in the extension process. [•] The addition of micron-sized WC particles can improve the fracture toughness obviously. [Copyright &y& Elsevier]

Abstract: Effects of carbon content on microstructure and properties of WC–20Co cemented carbides with carbon content from 4.45% to 5.25% prepared by sinter-HIP were analyzed by X-ray diffractometry (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), Rockwell hardness analysis, cobalt magnetic performance analysis, bending strength analysis and so on. The results show that carbon content plays a significant role in the phase composition and microstructure, WC grain size and shape, W solubility of the binder, and mechanical properties of cemented carbides. In the field of research, with increasing carbon content, the WC mean grain size increases and morphology characteristic of WC grains tends to show truncated trigonal prim shape. And carbon content also influences W solubility, so that in carbon-rich cemented carbides the binder dissolves about 4mass% tungsten and in carbon-deficient cemented carbides up to 20mass%. The density and Rockwell hardness of alloys decrease with increasing carbon content. On the contrary, the cobalt magnetic performance of alloys increases and the extent of variation gets smaller and smaller. The bending strength of alloys increases then substantially decreases with increasing carbon content and appears maximum in the two-phase region. [Copyright &y& Elsevier]

Abstract: Ultrafine WC–Co cemented carbides doped with 0, 0.5, 1, 1.5 and 2wt.% Cu were fabricated by the sintering/hot isostatic pressing (sinter–HIP) process for the mixed WC and chemical precipitated Co–Cu powders. The Vickers hardness of cemented carbides was measured at temperatures ranging from room temperature to 800°C. The Cu-doped WC–Co alloys with the higher proportion of WC hard phase and finer microstructure of the average grain size of 590nm exhibit the higher hardness at the elevated temperature of 800°C. The Cu-doped WC–Co cemented carbides have a potential application in machining. [Copyright &y& Elsevier]

Abstract: The friction and wear behaviors of WC/Co cemented carbide tool materials with average WC grain sizes ranging from 0.6 to 2.2μm were evaluated in ambient air at temperatures up to 600°C using a ball-on-disk high temperature tribometer. The friction coefficient and wear rate were measured. The microstructural changes and the wear surface features of the WC/Co cemented carbides were examined by scanning electron microscopy. Results showed that the friction coefficient of WC/Co cemented carbides decreased with the increase of test temperature. All the tested samples showed the highest friction coefficient when sliding at 200°C, and exhibited the lowest friction coefficient in the case of 600°C. The wear rate of WC/Co cemented carbides increased with the increase of test temperature. The cemented carbide with the smallest WC grain size showed improved wear resistance at temperature up to 600°C, which corresponds to its higher value of hardness. The difference of the worn surface features of the WC/Co cemented carbide after sliding at different temperature is related to the chemical transformation during sliding wear tests. Abrasion and grain cracking seemed to be the main wear types at temperature less than 200°C, the wear owing to binder removal by plastic deformation and grain pull out were suggested to be the main wear mechanism at intermediate temperature, while the mechanism of oxidative wear dominated at 600°C. [Copyright &y& Elsevier]

Abstract: Most materials exhibit a decreased toughness as the hardness (or strength) increases. Here we report a new strategy to combat this problem for cemented carbides (WC-Co). Instead of suppressing the growth of WC grains during sintering, we allow nano-WC particles to grow in a controlled manner, leading to the formation of thin WC platelets with a high aspect ratio. The thin thickness offers high hardness, while the high aspect ratio provides superior toughness. As a result, the bulk WC-Co produced from the nanocrystalline powder bucks the unfavorable trend exhibited by most of the cemented carbides available today – showing simultaneous improvements in hardness and toughness. The principle discovered in this study has significant impact on WC-Co and offers new opportunities to obtain superior mechanical properties for other cermets and advanced ceramics as well. [Copyright &y& Elsevier]

• Ultrafine-grained cemented carbides are prepared by in-situ synthesis route. • Elements of W, Co and V are uniformly distributed in the finally sample. • High C/WO 3 ratio and appropriate addition amount of VC can improve performances. WC-12Co- x VC cemented carbides were synthesized using an in-situ synthesis method consisting of precursor formation, deoxidization and carbonization-sintering steps. The experimental results showed the mean grain size of the WC in the sintered alloys decreased from 1.05 to 0.46 and 2.13–0.57 µm, corresponding to the VC content from 0 to 2 wt% at 1350 °C and 0–6 wt% at 1400 °C. V 4 WC 5 thin-layer was generated in the final sintered sample with low VC addition. As the VC content increased to more than 2 wt%, the V 4 WC 5 with larger particles size were generated except the V 4 WC 5 thin-layer, which would effectively enhance the hardness of WC-12Co-VC cemented carbides. The fracture toughness reached the maximum value of 16.45 MPa·m1/2 for WC-12Co-2VC sintered at 1350 °C for 2 h; while the Vickers hardness reached the maximum value of 2124 HV for WC-12Co-6VC sintered at 1400 °C for 2 h, respectively. [ABSTRACT FROM AUTHOR]

This study investigates the influence of milling parameters and sintering cycle on the microstructure and properties of cemented carbides with an overal WC–11.5wt%Fe–4wt%NbH–0.5wt%C starting powder composition. The raw material powders were milled and mixed in a ring mill or planetary ball mill and sintered at 1150, 1200 or 1250 °C using spark plasma sintering (SPS). The cemented carbide density, Vickers hardness and fracture toughness were evaluated. The microstructure was investigated by optical and scanning electron microscopy using wavelength dispersive X-ray spectroscopy for elemental mapping. The transition from NbH to NbC was identified for all sintered materials. Moreover, microstructural gradients were formed creating bi-layered structured materials with higher hardness edges and tougher cores. The highest microstructural homogeneity and hardness were found for planetary ball milled starting powder sintered at 1250 °C. For these samples, the highest density recorded was 13.69 g/cm3, which also obtained highest hardness values of 1620 H v and 1589 H v , on the surface and center regions, respectively. [Display omitted] • The (Fe-NbH-C) system was applied in an unprecedented way as an alternative binder for cemented carbides. • Ring and planetary ball milling techniques were compared. • SPS technique created bi-layered structured cemented carbides with higher hardness edges and tougher cores. • An increased sintering temperature resulted in homogeneous and dense microstructures. [ABSTRACT FROM AUTHOR]

Abstract: Hardness of WC–Ni cemented carbides with tiny addition of TiC is studied. The addition of TiC changes the shape of WC crystals to a flatter triangular prism with lower value of the shape equiaxiality P WC. The hardness increases 8–15% on the alloys with lower value of P WC. It is shown that none of the existing models for hardness can explain the effect of the shape. A modification to Hall–Petch relation and Lee & Gurland model for hardness is suggested to accommodate the anisotropy and the shape of WC crystals. The mean linear intersections of the carbide and binder phases are multiplied by the normalized shape equiaxiality . The modified Lee & Gurland model for anisotropic WC crystals gives a satisfactory fit to the experimental data. In addition, the relationships between fracture toughness and strength vs. hardness for these cemented carbides are presented and discussed. [Copyright &y& Elsevier]

Abstract: The microstructure and properties of (W,Ti)C cemented carbides with a different metal binder composition of Ni and Co fabricated by powder technology were investigated. The densifications of the prepared materials were accomplished by using vacuum sintering at 1450°C. Nearly fully dense (W,Ti)C cemented carbides were obtained with a relative density of up to 99.7% with 30wt% Co and 99.9% with 30wt% Ni. The average grain size of carbides for the (W,Ti)C–Co and the (W,Ti)C–Ni was decreased with increasing the metal binder content. The hardness of the dense (W,Ti)C–15wt%Co and (W,Ti)C–15wt%Ni, was greater than the hardness of other different compositions of (W,Ti)C–Co and (W,Ti)C–Ni cemented carbides respectively; in addition, the (W,Ti)C–Co cemented carbides had greater hardness values than the (W,Ti)C–Ni cemented carbides. The magnetic properties, which were measured at an applied field of 0.8T, indicate that the (W,Ti)C–Co cemented carbides have ferromagnetic properties with a higher magnetic saturation with higher cobalt content as well as higher coercivity with lower cobalt content. On the other hand, the (W,Ti)C–Ni cemented carbides are non-magnetic on account of the very low magnetic saturation and they have lower coercivity values than the (W,Ti)C–Co cemented carbides. [Copyright &y& Elsevier]

Abstract: An analytical model to calculate the hardness of ultra-fine WC–10Co cemented carbides was investigated. The nanocrystalline WC–10Co powders were manufactured using a spray conversion process and sintered at 1375°C in a vacuum. Varying amounts of TaC, Cr3C2, and VC were added to nanocrystalline WC–10Co cemented carbides as grain growth inhibitors. The hardness of WC–10Co cemented carbides increased with a decreasing WC grain size from 5μm to 300nm. An analytical model to calculate the hardness of WC–10Co cemented carbides was proposed under the assumption that the applied load is transferred from the WC to the Co binder phase. The analytically calculated hardness showed good agreement with the experimentally measured hardness of WC–10Co cemented carbides. In the proposed analytical model, the hardness of WC–10Co cemented carbides is similar to that predicted by the Hall–Petch relationship when the WC grain size is large. However, when the grain size is finer than a critical value, the predicted hardness of the WC–10Co cemented carbide becomes saturated. [Copyright &y& Elsevier]

Abstract: The structure and hardness of a WC-10wt% Co alloy prepared with an experimental WC powder are compared with those of another alloy of the same composition produced under the same conditions and prepared with a commercial WC powder. The experimental WC powder was synthesized by a gas–solid reaction between APT and methane at low temperature and the commercial WC powder was conventionally produced by a solid–solid reaction between tungsten and carbon black. WC-10wt% Co alloys with the two powders were prepared under the same conditions of milling and sintering. The structure of the sample prepared with the experimental WC powder is homogeneous and coarse grained. The structure of the sample prepared with the commercial powder is heterogeneous. Furthermore the size and shape of the WC grains are significantly different. [Copyright &y& Elsevier]

Abstract: In this study, large additions of VC or VC and TiC were made to WC–Co cemented carbide to create a harder and more wear-resistant material. The effectiveness of Ti as a grain growth inhibitor was investigated. Backscattered electron SEM imaging of the microstructure of WC–VC–Co revealed a core–rim structure in the (W,V)C grains. SEM–EDS revealed a composition gradient in these (W,V)C grains. These results were confirmed by bright-field TEM investigations, which showed the presence of a core–rim structure and dislocations in the core–rim interface. Backscattered electron SEM imaging did not show a core–rim structure in (W,Ti,V)C grains, and this result was confirmed by SEM– and TEM–EDS analyses, which did not reveal any evidence of a composition gradient in these grains. The lattice parameters of (W,V)C and (W,Ti,V)C were determined, using XRD, and found to be 0.420nm and 0.429nm, respectively. The Co binder composition of both materials was found to be similar. The average grain size of the cubic carbides decreased from 2.0 to 1.7μm and the grain size distribution became more narrow with the addition of TiC, and the HV30 hardness increased from 1519 to 1549. A model for the hardness of WC–Co with large cubic carbide additions is proposed. [Copyright &y& Elsevier]

Abstract: Nanometer WC–Co powder was hot pressed in order to develop new processes and improve the properties of WC–Co cemented carbides. Density and hardness were measured. The microstructures of sintered alloys were observed by SEM. And the grain size of WC in alloys was also measured. The results show that hot pressing can lower the sintering temperature by about 100°C, increases the density (more than 99%) and circumscribes the growth of grain size (smaller than 1μm) of alloys. Hardness can also be improved up to HRA 92 by this process. Hot pressing is an effective method to get WC–Co cemented carbides with fine grain size and good properties. [Copyright &y& Elsevier]

Abstract: Microstructure and mechanical properties of WC–TiC–10wt%Co cemented carbides fabricated by sintering with hot isostatic pressing (Sinter-HIP) process were investigated. The WC/TiC grain size ratio of WC–TiC–10wt%Co cemented carbides was controlled by changing the average size of WC powders ranged from 0.5 to 4μm, with keeping the average size of TiC powder as 1μm. The microstructures of sintered WC–TiC–10wt%Co cemented carbides were sensitively dependent on the WC/TiC grain size ratio. In WC–TiC–10wt%Co cemented carbides with WC/TiC grain size ratio of 0.5, the TiC/(Ti,W)C core-rim phases were distributed in WC/Co matrix. While, in WC–TiC–10wt%Co cemented carbides with WC/TiC grain size ratio above 0.8, the WC and TiC/(Ti,W)C core-rim phases were surrounded by Co binder phase. Hardness of WC–TiC–10wt%Co cemented carbide increased with decreasing the WC/TiC grain size ratio from 4 to 0.8 following the modified Hall–Petch type equation. However, the hardness of WC–TiC–10wt%Co cemented carbides with WC/TiC grain size ratio of 0.5 shows much higher values than that expected by modified Hall–Petch type equation. Transverse rupture strength of WC–20TiC–10wt%Co cemented carbides increases with decreasing the WC/TiC grain size ratio. [Copyright &y& Elsevier]

Microstructure and mechanical properties of WC–10Co cemented carbides fabricated by spark plasma sintering (SPS) process were investigated. Nanocrystalline precursor powders were prepared by spray drying process from solution containing ammonia meta-tungstate and cobalt nitrate, and followed by reduction and carbonization into nanocrystalline WC/Co composite powders by a mechano-chemical process. The WC particles of about 100 nm in diameter were mixed homogeneously with Co binder. The nanocrystalline WC–10Co powders were consolidated by SPS process at temperature ranged 900–1100 °C and under a pressure of 50 or 100 MPa, respectively. Optimum consolidation conditions, such as temperature and pressure, were determined by analysing the dimensional changes of powder compact during SPS process. Hardness and fracture toughness of consolidated WC–10Co cemented carbide were measured by using a Vicker''s indentation test. The solute content within the Co binder phase of WC–10Co cemented carbide was evaluated by measuring the saturated magnetic moment. It is found that the hardness of cemented carbide was dependent on the density and grain size of WC. The fracture toughness of cemented carbides increased with increasing the saturated magnetic moment, while decreased rapidly when the liquid Co phase was formed during sintering. [Copyright &y& Elsevier]

A new model for the hardness of cemented carbides is proposed. The model is based on the main assumption that very thin binder layers (a few atom layers) confined between hardphase grains are forced to behave mechanically as the confining material. When increasing the binder layer thickness, the influence from the hardphase will decline, following an exponential relationship. This model has the advantages over current models that it predicts the hardness from data on carbide grain size and volume fraction only, without the need for the laborious carbide contiguity value. It also covers a wider range of carbide grain sizes and binder volume fractions than do the current models. The model has been verified on a very wide range of cemented carbide compositions, covering a hardness interval of 800–2400 Vickers. Throughout this interval, the calculated hardness values agree to within 15% to the measured values. This makes the model a useful tool in the development of new WC–Co grades, for the interpretation of wear results and for estimating grain size and cobalt volume fraction values. [Copyright &y& Elsevier]

In this work more than 2500 published experimental data on hardness and indentation fracture toughness of cemented carbides during the last 40 years have been collected. The significant number of samples displays the influence of microstructure, chemical composition, and processing on the hardness - toughness relationship of cemented carbides. Selected two-dimensional plots are presented and discussed as an example of visualization of the available experimental information. This collected record can serve as an initial reference set for the cemented carbide community using all available shared knowledge organized in one well-structured database. [Display omitted] • 2500 published experimental data on hardness and indentation fracture toughness of cemented carbides • Shared knowledge of cemented carbides during last 40 years organized in structured database • Microstructure, chemical composition and processing influence on the Hv-K IC of cemented carbides • Selected two-dimensional Hv-K IC plots for visualization of the available experimental information [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]