Effects of carbothermal prereduction temperature and Co content on mechanical properties of WC–Co cemented carbides

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 m^1/2, 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.     

Effects of oxide addition on structure and properties of WC–10Co cemented carbide obtained by in situ synthesized powder

Combining spray drying and in situ synthesized technology, WC–10Co cemented carbide with uniform composition was prepared by vacuum sintering. The effects of Al₂O₃ and additions of different rare-earth oxides (La₂O₃, Y₂O₃ and CeO₂) on the microstructure and mechanical properties of WC–10Co were investigated. As the Al₂O₃ content increased from .5 to 2 wt%, the hardness of the sintered sample increased, whereas the relative density and fracture toughness decreased. Compared with the addition of .5 wt% Al₂O₃, the WC–10Co alloy with .5 wt% rare-earth oxides had higher hardness. In addition, compared with the alloy without an inhibitor (.80 μm), after adding .5 wt% Al₂O₃, La₂O₃, Y₂O₃ and CeO₂, the WC grain sizes were reduced to .73, .65, .71 and .62 μm, respectively, which indicated that the addition of Al₂O₃ and rare-earth oxides could refine WC grain during sintering. Among these additives, CeO₂ had the best effect. With the addition of .5 wt% CeO₂, the hardness and the fracture toughness increased from 1299 to 1710 HV₃₀ and from 16.18 to 18.90 MPa m^1/2, respectively.     

Influence of Cu-coated diamond addition on the microstructure and mechanical properties of WC-based cemented carbides

Cu-coated diamond enhanced tungsten carbide powder (WC)-Ni cemented carbides were successfully fabricated by spark plasma sintering method. Characterization of the phase composition and microstructure reveal that the diamond particles are well preserved and homogeneously distributed in the composites. Relative density of the samples improved from 92% to 97.6% with 2 wt% Cu-coated diamond addition. Vickers hardness and flexural strength of the samples achieved the maximum value of 2000 HV₁₀ and 950 MPa with 8 and 2 wt% addition, respectively. The fracture toughness improved from 8 to 11 MPa m^1/2 with the added content of diamond increasing from 0 to 4 wt%. The wear rate of the sample is reduced by five times with 6–8 wt% Cu-coated diamond addition. The wear mechanism mainly includes the removal of binder phase, the crushing of WC grains, and the crushing and pulling out of diamond particles.     

Effect of SiC nanowhisker addition on microstructure and mechanical properties of regenerated cemented carbides by low-pressure sintering

The hardness and toughness of regenerated cemented carbides, in general, are contradictory. Therefore, it is critical to explore regenerated cemented carbides with both high hardness and high toughness. In this study, regenerated WC-8-wt% Co cemented carbide with SiC nanowhisker were prepared by low-pressure sintering. The influence of SiCw contents on the microstructure and mechanical properties of regenerated WC-8-wt% Co cemented carbide was investigated. The results indicated that the hardness, density, flexural strength, and fracture toughness of regenerated cemented carbide first increased and then decreased with the addition of SiCw. The Vickers hardness, density, flexural strength, and fracture toughness could reach 1575 HV, 14.6 g/cm³, 2204 MPa, 16.85 MPa·m^1/2, respectively, with SiCw content 0.5 wt%, which were increased by 14.4%, 0.7%, 12.2%, and 17.3%, respectively, when compared with the regenerated cemented carbide without SiCw. The lowest friction coefficient and the best wear resistance could be also reached when 0.5-wt% SiCw was added. The fracture mechanism of the regenerated cemented carbide contained both transgranular and intergranular fracture through the microscopic observation of fracture surface via scanning electron microscope.     

Effect of carbon nanotubes additives on mechanical properties of WC–6Co cemented carbide

In order to increase the toughness of WC–6Co cemented carbide, different contents of carbon nanotubes (CNTs) were added to the WC–6Co alloy powder to prepare cemented carbide by low-pressure sintering. The results showed that some of the CNTs were embedded between the grains of WC–6Co cemented carbide, which would hinder the growth of WC grain boundary, thus leading to grain refinement. In addition, CNTs inhibited the formation of decarbonized phase and guided the deflection and bridge of crack to hinder the crack extension. With the increase of CNTs content, the density increased at first and then decreased, and the transverse fracture strength increased at first and then decreased. When the content was 0.2 wt.%, the alloy had the best performance. The density of the alloy was 99.67%; the transverse fracture strength was up to 2937.5 MPa, which is about 100% higher than that of cemented carbide without CNTs. The fracture toughness was 9.84 MPa m^1/2, and the hardness was 1924.8HV₃₀.     

Performance and wear mechanism of spark plasma sintered WC-Based ultrafine cemented carbides tools in dry turning of Ti–6Al–4V

Cutting performance and failure mechanisms of spark plasma sintered (SPS) ultrafine cemented carbides in dry turning Ti–6Al–4V were studied. The tools of UYG8 (WC-8wt%Co) and UYG8V2B10 (WC-8wt%Co-0.2 wt%VC-1.0 wt%cBN) exhibited higher lifetime and better processing quality than the commercial YG8 cemented carbide tool. The cutting distance of UYG-8 and UYG8V2B10 tools are 1.8 and 1.6 times longer than that of YG8, respectively. Cutting-edge breakage was found as the main failure forms of the SPS cemented carbide tools containing low Co content (≤6 wt%), whereas the SPS cemented carbide tools containing high Co content (≥8 wt%) exhibited flank and rake wear as main failure forms caused by abrasion, adhesion, diffusion, and oxidation. UYG8V2B10 tool wear mechanism was affected by cutting speed and depth. Wear mechanisms of UYG8V2B10 tool are mainly adhesive wear and oxidative wear at low cutting speed, but follow adhesive wear and diffusive wear at higher cutting speed. Moreover, with increasing cutting depth, tool failure forms are mainly breakage and chipping, largely induced by high cutting temperature and severe cutting vibration.     

Tool life and wear of WC–TiC–Co ultrafine cemented carbide during dry cutting of AISI H13 steel

WC–5TiC–10Co ultrafine cemented carbides were prepared and used for the cutting tool for AISI H13 hardened steel. The effect of cutting parameters on the tool life and tool wear mechanism was investigated, and conventional cemented carbide with the same composition and medium grain size were prepared for comparison. The results showed that WC–5TiC–10Co ultrafine cemented carbides possess higher hardness and transverse rupture strength, and showed better cutting performance than conventional insert with the same cutting condition. Tool life was analyzed by an extended Taylor's tool life equation, indicating that cutting speed played a profound effect on the tool life and wear behavior of both cutting inserts. SEM and EDS analysis revealed that there were major adhesive wear and minor abrasive wear on the rake of WC–5TiC–10Co ultrafine inserts, and increase of cutting speed resulted in a transition from abrasion predominant wear mechanism to adhesive wear on the flank face. As for the conventional inserts, there were combination of more serious abrasive and adhesive wear on the rake and flank. The favorable cutting performance of ultrafine WC–5TiC–10Co inserts was attributed to the higher hardness and less thermal softening during machining.     

The effects of fine WC contents and temperature on the microstructure and mechanical properties of inhomogeneous WC-(fine WC-Co) cemented carbides

Inhomogeneous WC-(fine WC-Co) cemented carbides with improved hardness and toughness were successfully prepared through the addition of fine WC using planetary ball milling combined with sinter isostatic hot pressing (SHIP) technology. The inhomogeneous microstructure of the alloys consisted of coarsened WC grains and WC-Co consisting of fine WC dispersoids and Co binder phase. The increase of temperature and the addition of fine WC enhanced the sintering process. The morphologies of the coarsened WC and of the fine WC consisted of triangular and near-hexangular prisms, respectively. Due to crack path deflection and crack bridging, the prism-like coarsened WC crystals efficiently hindered cracks propagation. Intergranular fracture became predominant when adding fine WC. However, the excessively coarsened WC and some pores in alloys with 20 wt% fine WC could decrease the mechanical properties. The inhomogeneous WC-(fine WC-Co) cemented carbides with 10 wt% fine WC, sintered at 1430 °C for 40 min, could provide a combination of superior hardness and toughness.     

Fabrication and performances of WC-Co cemented carbide with a low cobalt content

WC-Co cemented carbides with a low cobalt content (≤3 wt.%) were successfully manufactured by the powder metallurgy method. The cobalt content is lower than conventional cemented carbide (3–30 wt.%), which makes the prepared alloys possess excellent hardness. The effects of cobalt content on the densification behavior, phase composition, micromorphology, and mechanical performances of cemented carbides were investigated in detail. The results revealed that all the sintered alloys were almost completely consolidated with a relative density of greater than 98.0%. Moreover, abnormal grain growth was observed, and the inhomogeneity of WC grains decreased with the increment in cobalt content. In order to obtain cemented carbides with homogeneous microstructure and outstanding performances, VC was added to inhibit grain growth. Microstructure and performances were significantly affected by the addition of VC. The maximum Vickers hardness of cemented carbides without the addition of vanadium was 2234 HV30, while the fracture toughness was 7.96 MPa·m^1/2 after sintering WC-2 wt.%Co. After adding VC, the ultimate hardness and fracture toughness of WC-3 wt.%Co-0.5 wt.%VC alloy could reach 2200 HV30 and 8.61 MPa·m^1/2, respectively. In addition, the obvious crack deflexion and transgranular behavior can be noticed, which can prevent the extension of crack and achieve an increase in fracture toughness of cemented carbides.     

Improvement of microstructure,mechanical properties and cutting performance of Ti(C,N)-based cermets by ultrafine La2O3 additions

Ti(C,N)-WC-Mo₂C-TaC-Co-Ni cermets with various content of La₂O₃ were prepared by gas-pressure sintering at 1450 °C. The effects of ultrafine La₂O₃ additions (0, 0.05, 0.1 and 0.2 wt%) on the microstructure, mechanical properties, wear resistance and cutting performance of cermets were explored. In the microstructure of cermets, the La₂O₃ particles and dissolved La element in binder phases were observed, which could inhibit the dissolution-precipitation process of ceramics phases during liquid-sintering. Furthermore, the La₂O₃ could absorb and react with the impurity Al element with low melting point from raw powders, avoiding the appearance of liquid phase at the low temperature and partial overheating during sintering process. These mechanisms could inhibit the abnormal growth of Ti(C,N) core-(Ti,W,Mo,Ta)(C,N) rim structures effectively, leading to the thinning of brittle rim phases and coarsening of wear-proof Ti(C,N) particles. The decrease of proportion of brittle rim phase and ultrafine Ti(C,N) particles promoted the fracture toughness. The increase of proportion and grain size of Ti(C,N) improved the hardness, wear resistance and cutting performance significantly. However, the excessive addition of La₂O₃ would result in the agglomeration of La₂O₃, causing the sharp decline of mechanical properties and cutting performance. The cermet with 0.1 wt% La₂O₃ addition possessed the optimal mechanical properties with Vickers hardness, transverse rupture strength and fracture toughness of 1710 (HV30) Kgf/mm², 2480 MPa and 11.7 MPa m^1/2, respectively.     

Effect of the Cubic Phase Distribution on Ultrafine WC–10Co–0.5Cr–xTa Cemented Carbide

The (Ta, W)C cubic phase distribution plays a key role in the microstructure and mechanical properties of ultrafine WC–Co–Cr₃C₂–TaC cemented carbides. By integration of thermodynamic calculations and key experiments, the influence of the cubic phase distribution in ultrafine WC–10Co–0.5Cr–xTa cemented carbides was systematically investigated. A series of ultrafine grained cemented carbides were designed and fabricated through ball‐milling and vacuum sintering at 1410°C for 1 h. The microstructure was investigated using scanning electron microscopy (SEM). The electron backscattered diffraction (EBSD) was used to measure the orientation and size of cubic phase segregation. The results indicate that the cubic phase in the microstructure distributes more heterogeneously in the range of 0.2 to 0.7 wt% Ta addition, but finally the isolated cubic phase is homogeneously distributed with a Ta content from 0.7 to 1 wt%. Combining the thermodynamic calculation with the experiment, the mechanism for the microstructure evolution has been revealed. The mechanical properties of alloys substantially depend on the cubic phase distribution in the microstructure. A synergetic correlation between the transverse rupture strength (TRS) and Rockwell hardness was observed. The homogeneity of cubic phase can be designed and controlled effectively via the present approach.     

A study of CVD diamond deposition on cemented carbide ball-end milling tools with high cobalt content using amorphous ceramic interlayers

In this paper, CVD diamond coatings are deposited on cemented carbides with 10 wt.% Co using amorphous SiO₂ and amorphous SiC interlayers. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Raman spectrum and X-ray diffraction (XRD) are carried out to characterize the microstructure and composition of as-deposited films. Moreover, the adhesion and cutting performance of as-fabricated diamond coatings are studied. Indentation tests show that the amorphous ceramic interlayers can enhance the adhesion between diamond films and WC–Co substrates. The cutting tests against zirconia indicate that the tools with amorphous ceramic interlayered diamond coatings exhibit improved cutting performance. The amorphous ceramic interlayers can improve the adhesive strength and wear endurance of diamond coatings on WC–10 wt.% Co substrates, which provide a viable way for adherent diamond coatings on cemented carbide tools with high cobalt content.     

Effect of WC particle size on the microstructure and mechanical properties of Ni–Co coarse grain cemented carbide

The effect of different WC grain size additions on the microstructure and grain distribution of Ni–Co coarse crystalline cemented carbide was studied. And then the effect of grain distribution on the mechanical properties of cemented carbide was discussed. The effect of WC grain size on the grain size and coherency of cemented carbide was analyzed by microstructure. And the distribution of grains in the microstructure was investigated by the truncation method. The addition of fine (1.1–1.4 μm), medium (2.3–2.7 μm), and coarse WC (5.6–6.0 μm) particles can increase the nucleation rate of WC grains in the bonded phase. And the higher grain growth driving force can produce the theoretical limitation of nucleation and inhibit the coarsening of WC grains to a certain extent. The WC grain size has an insignificant effect on the frequency of the occurrence of super-coarse grains in coarse crystalline cemented carbide. The average grain size and super coarse grains in microstructure gradually decrease, which promotes the improvement of transverse rupture strength. The increase of the adjacent degree and the decrease of the mean free path reduce which is beneficial to the improvement of the corrosion resistance of the alloy. The best overall performance of the alloy is achieved when fine-grained WC is added.     

Tool life and wear mechanism of WC–5TiC–0.5VC–8Co cemented carbides inserts when machining HT250 gray cast iron

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.     

The two dimensional microstructure characterization of cemented carbides with an automatic image analysis process

The traditional two dimensional microstructure characterization of cemented carbide, based on stereology of linear intercept method, requires tedious and subjective manual measurements. In this study, an automatic image analysis procedure with two key techniques, i.e. maximum class square error method and watershed transformation method, has been successfully developed. The image analysis for WC-16Co cemented carbides with this procedure easily acquires consistent microstructure parameters. The analysis for area weighted WC grain size, as well as the subsequent mean free path of Co binder show quite different results compared with the conventional number weighted data. It is found that for both number weighted and area weighted data, the contiguity of WC/WC grains is insensitive to the variation of either mean WC grain size or mean free path of Co binder. The mean WC grain size is linearly related to the mean free path of Co binder. The hardness of cemented carbide, having a linear relationship with the inverse square root of mean WC grain size, conforms to Chermont and Osterstock's model. Although it is too early to conclude whether number weighted or area weighted WC grain size (and subsequent mean free path of Co binder) is better, this study shows that area weighted WC grain size and the corresponding mean free path of Co binder are more suitable for Chermont and Osterstock's hardness modeling compared with number weighted WC grain size. The area weighted WC grain size and subsequent mean free path of Co binder, which have rarely been considered for microstructure characterization of cemented carbide previously, could be the key parameters for a better understanding of the microstructure evolution, as well as a better mechanical behavior modeling for cemented carbide.     

Effect of carbon content on microstructure and mechanical properties of WC-10Co cemented carbides with plate-like WC grain

Four sets of WC-10Co cemented carbides with different carbon content were prepared by adding the ultrafine WC powders as seeds during the in-situ sintering reaction among W, Co and C. The effect of carbon content on microstructure and mechanical properties were studied. The results show that the microstructure, phase composition and mechanical properties of WC-10Co cemented carbides with plate-like WC grains were seriously affected by the carbon content. The fast growth of WC grains with high carbon content could proceed the prismatic plane preferentially along the <1 0 $1(-)$ 0> directions, resulting in the high content of plate-like WC grains. The density increased with the increment of the carbon content and reached the maximum value, then, followed by a decline. The hardness and the transverse rupture strength of the alloy in the two-phase zone with carbon content of 5.91 wt% reached the maximum value. The existence of plate-like WC grains could impede the propagation of the cracks due to the decrease of the weakest carbide regions and the increase of the basal facets of broken WC crystals. In this case, more fracture energy was required to crack propagation and further improved the transverse rupture strength. Additionally, the plate-like WC was benefit to reduce the wear volume and bring about a better wear resistance. Thus, the alloy with the appropriate proportion of carbon content can obtain higher mechanical properties and wear resistance.     

Effects of GNP on the mechanical properties and sliding wear of WC-10wt%Co cemented carbide

WC-10Co cemented carbides reinforced with 0, 0.5, 1, and 2 wt% graphene nanoplatelet (GNP) were fabricated by ball milling and spark plasma sintering (SPS). The microstructure, structural and phase analysis, hardness, and fracture toughness of WC-10Co/GNP composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and Vickers indenter. Tribological behaviors of the fabricated composites against an alumina counterface were studied using a pin on disk configuration. It was found that GNP refined the microstructure, increased the fracture toughness, and postponed the stable-to-unstable friction transition. While transgranular fracture and crack deflection were observed in the base composite, crack bridging, micro-crack formation, and crack deflection were the major toughening mechanisms in GNP-reinforced cemented carbides. The addition of 1 wt% GNP resulted in the highest hardness and wear resistance. However, at higher GNP contents, both hardness and wear resistance decreased due to the agglomeration of GNPs. Widespread abrasive grooving and Co binder extrusion were characterized as the main controlling mechanisms of wear in GNP-free cemented carbides. The wear of GNP-reinforced cemented carbides was dominated by the formation of a lubricating surface layer and its cracking or fragmentation. Plastic flow is much less likely to occur in the presence of GNPs.     

Effect of co-addition of SiC and WC on the densification behaviour and microstructural evolution of TiC-based composites

In the present study, the effect of simultaneous incorporation of SiC and WC additives on the densification behaviour and microstructural development of TiC-based composites is studied. Four different TiC-SiC-WC (TSW) composites with varying SiC and WC content were synthesized by ultrasonic wet milling followed by spark plasma sintering (SPS) at 1750 °C for 5 min under 40 MPa external pressure. The average particle size of the ultrasonic wet-milled mixture underwent an appreciable refinement from 2.48 μm (un-milled powder) to between 0.9 and 1.25 μm. The sintered compacts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and thermodynamic assessment. All TSW sintered specimens exhibited a relative density of greater than 98% with TiC +10 wt% SiC +15 wt% WC reaching the highest value of 99.2%. The XRD analysis and microstructural evaluation confirmed the in-situ formation of Ti₃SiC₂ compound for specimens TiC +15 wt% SiC +10 wt% WC and TiC +20 wt% SiC +5 wt% WC as suggested by the thermodynamic evaluation. Besides, except for specimen TiC +20 wt% SiC +5 wt% WC, some of the SiC grains with unclean grain boundaries were found to be dissolved partially within the (Ti, W) C solid solution, thereby indicating the formation of (Ti, W, Si) C solid solutions as confirmed by the SEM/EDS analysis. The optimum hardness and indentation fracture toughness of 22.43 GPa and 6.54 MPa m^½ were obtained for the samples TS10W15 and TS15W10, respectively. Crack deflection, branching, and bridging induced by the untwine SiC grains, partly un-dissolved WC particles, and (Ti, W) C solid solution phase are among the main toughening mechanisms responsible for improving the fracture toughness of the co-reinforced specimens besides the break of intertwining SiC grains.     

Effect of Binder Content on the Erosive Wear of Ti(C,N)‐Based Cermet in SiO2 Particle‐Containing Simulated Seawater

Erosion of Ti(C,N)‐10 wt% Mo₂C‐15 wt% Ni/Co cermet of different Ni/Co in artificial seawater containing 5 wt% SiO₂ was investigated. Pure Ni‐bonded cermet exhibited the largest wear rate of 35.7*10^?3 mm³/h, which decreased to 17.7*10^?3 mm³/h with the substitution of 30% Ni by Co. Further decrease of Ni/Co ratio resulted in the improvement of erosion resistance. Pure Co binder resulted in the increase hardness from 92.0 to 92.5 HRA and transverse rupture strength from 1510 to 1650 MPa. The erosion resistance was slightly worse due to an increasing hardness and brittleness of the binder phases, but the hard phases still kept the as‐prepared morphology.     

Effects of metal phases on microstructure and mechanical properties of microwave-sintered Ti(C,N)-based cermet tool

A kind of Ti(C, N)-based cermet tool material was prepared by microwave sintering. The influence of metal phases (Ni, Co, and Mo) on densification and mechanical properties was studied by orthogonal test. The results indicated that Co was more significant in improving relative density and fracture toughness than Ni, while Ni and Co had the similar effects on increasing the hardness of Ti(C, N)-based cermet. Mo can improve fracture toughness but decrease hardness. Ti(C, N)-based cermet with 6 wt% Ni, 6 wt% Co and 6 wt% Mo (TN6C6M6) had the optimal comprehensive mechanical performances, and its fracture toughness and hardness were better than that of Ti(C, N)-based cermet prepared by conventional sintering. The increasing of sintering temperature promoted the uniformity of microstructure and significantly improved densification and hardness of the Ti(C, N)-based cermet. The highest fracture toughness of TN6C6M6 (12.41 ± 0.33 MPa·m^1/2) was achieved when sintered at 1600°C. For the microwave-sintered Ti(C, N)-based cermet, heat preservation period had little effect on densification. The relative density can reach up to 98.6% even though the heat preservation period was 0 minute.