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.     

Microstructure,mechanical properties,and cutting performances of WC-Co cemented carbides with Ru additions

In this study, the microstructure, mechanical properties, and cutting performance of WC-8Co cemented carbide with different Ru additions were studied in detail. The results show that Ru can inhibit the abnormal growth of WC grains and the mean grain size of WC grains decreases. Ru can result in the lattice distortion of Co phases and promote the phase transition of Co from face-centered cubic (FCC) to hexagonal closepacked (HCP) as Ru can reduce the stacking fault energy of Co phases. The proportion of HCP Co phases increased from 14.4 to 39.6% with increasing Ru content. Meanwhile, among the five groups of cemented carbides with different Ru additions, cemented carbides with 1.5 wt% Ru exhibit the highest hardness of 1382 HV and transverse rupture strength (TRS) of 3790 MPa. The enhanced hardness and TRS were due to solid solution strengthening and phase transition of Co, respectively. The fracture toughness of cemented carbide was enhanced from 16 MPa m^−1/2 with 0 wt% Ru to 19 MPa m^−1/2 with 0.5 wt% Ru. Additionally, during the dry cutting of Ti–6Al–4V, the diffusion of Ti and Al elements is hindered. Therefore, the wear resistance of the tools is improved. The cutting lifetime of the cemented carbide tools with 0.5 wt% Ru increased three-fold compared to those without Ru addition.     

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.     

Microstructure and properties of WC-8Co cemented carbides prepared by multiple spark plasma sintering

In this study, WC-8Co cemented carbides were prepared by spark plasma sintering. When the samples sintered at 1300℃ were cooled to room temperature, the samples were sintered multiple times at 1250℃. The changes in microstructure and mechanical properties of WC-8Co cemented carbides prepared by multiple spark plasma sintering were studied. The hardness of cemented carbides increased in the first two sintering, reaching 16.5 GPa. However, the hardness decreased seriously in the last two sintering. The attenuation rates of hardness were 6.2% and 2.5% due to the abnormal coarse grains. Furthermore, the crack path along the grain boundary was almost straight, causing a decrease in the indentation fracture toughness of cemented carbides. Additionally, the grains of cemented carbides were abnormally coarsened, and the morphologies of grains became unstable due to multiple sintering.     

Effects of composite binder phase on microstructure and mechanical properties of ultrafine-grained cemented carbides

In order to develop a new high-performance binder phase, four different alloys Co-Ni-Fe, Co-Ni-Cr, Co-Ni-Nb, and AlCoCrNiNb_0.5 were used as a binder in cemented carbides. The room-temperature mechanical properties and high-temperature flexural strength of cemented carbides were studied. The results show that the optimal mechanical properties for the WC-8(Co-Ni-Fe, Co-Ni-Cr, Co-Ni-Nb, and AlCoCrNiNb_0.5) can be obtained at the sintering temperatures of 1200°C, 1350°C, 1350°C, and 1300°C, respectively. Compared with cemented carbides with Co as binder phase, the hardness of the four kinds of alloys is increased, the WC grain size becomes finer, but the fracture toughness is slightly decreased. When the temperature is under 600°C, there is no visible oxidation of the four kinds of cemented carbides, and their bending strengths are basically not reduced. When the temperature increased from 600°C to 900°C, the WC-8(Co-Ni-Nb) and WC-8(Co-Ni-Fe) samples present the better high-temperature bending resistance compared with the WC-8(Co-Ni-Cr) and WC-8AlCoCrNiNb_0.5 samples, with respective decrease in bending strength of 11.7% and 7.3%.     

Effects of powder preparation and sintering temperature on consolidation of ultrafine WC-8Co tool material produced by spark plasma sintering

In this study, ultrafine tool materials were produced by spark plasma sintering using three sets of WC-8Co nanopowders mixed by different methods. Effects of powder preparation method and sintering temperature on the consolidation of WC-8Co cemented carbides were investigated. At sintering temperature of 1250 °C, cemented carbide sintered from the powder mixed by ultrasonic vibration method exhibited homogeneous microstructure, high relative density (99.1%), small average grain size (280 nm), and excellent mechanical properties (H_V: 18.8 GPa, K_IC: 11.4 MPa⋅m^1/2). However, cemented carbide sintered from heavily ball-milled powder (ball milling for 24 h) showed increased grain coalescence and microdefects as well as lower relative density of 94.6%. Moreover, its hardness decreased to 17.7 GPa due to the decrease in relative density. Furthermore, straight cracks along grain boundary became dominant, causing fracture toughness to decrease to 10.5 MPa⋅m^1/2. Additionally, high sintering temperature caused grain coarsening, which was detrimental to mechanical properties of cemented carbides.     

Preparation and mechanical properties of SiCw-reinforced WC-10Ni3Al cemented carbide by microwave sintering

SiC_w-reinforced WC-10Ni₃Al cemented carbide was prepared by microwave sintering method, and the effects of the sintering temperature and SiC_w content on the microstructure and mechanical properties of WC-10Ni₃Al cemented carbide were investigated; the promotion effect and strengthening mechanism of SiC_w were then analysed. The experimental results showed that the relative density, hardness, flexural strength and fracture toughness of WC-10Ni₃Al cemented carbide increased and then decreased with increasing SiC_w addition and sintering temperature. When the sintering temperature was 1500 °C and the content of SiC_w was 0.3 wt%, the sample reached the highest mechanical properties and had a relative density of 96.5%, hardness of 1570 HV, flexural strength of 1275 MPa and fracture toughness of 13.1 MPa mm^1/2, which were 4.0%, 23.1%, 12.5% and 8.1% higher than those of the sample without SiC_w, respectively. During microwave sintering of WC-Ni₃Al, the addition of an appropriate SiC_w content can increase the microwave absorption of the sample, and produce many micro-high-temperature regions within the sample, which can accelerate the generation of the Ni₃Al liquid phase. This promotes liquid phase flow to fill pores and rearrange the WC grains, thereby improving density and mechanical properties of the sample. The strengthening mechanisms of SiC_w on microwave sintered WC-Ni₃Al consist of promoting densification enhancement, fine-grained strengthening, and solid solution strengthening of Ni₃Al by Si atoms.     

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.     

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.     

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.     

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.     

Preparation,mechanical properties,and toughening mechanisms of SiCw/SiCp-reinforced zirconia-toughened alumina ceramics

Zirconia-toughened alumina (ZTA) ceramics with high mechanical properties were sintered by hot-pressing method using SiC particles (SiCp) and SiC whiskers (SiCw) as the reinforcing agents simultaneously. The influences of sintering temperature, SiCp, and SiCw contents on the microstructure and mechanical properties of ZTA ceramics were investigated. It was found that both SiCp and SiCw could contribute to grain refinement significantly and promote the mechanical properties of the ceramics. However, the excess addition of SiCp or SiCw led to the formation of pores with large sizes and degraded the mechanical properties instead. When 13 wt% SiCp was introduced, the maximum flexural strength of 1180.0 MPa and fracture toughness of 15.9 MPa·m^1/2 were obtained, whereas the maximum flexural strength of 1314.0 MPa and fracture toughness of 14.7 MPa·m^1/2 were achieved at 20 wt% SiCw. Interestingly, the simultaneous addition of SiCp and SiCw could further improve the mechanical properties, and the highest flexural strength of 1334.0 MPa and fracture toughness of 16.0 MPa·m^1/2 were achieved at a SiCw/SiCp ratio of 16/4. The reinforcement mechanisms in the ceramics mainly included the phase transformation toughening of ZrO₂, the crack deflection and bridging of SiCp and SiCw, and the pull-out of SiCw.     

Influence of sintering temperature on microstructure and mechanical properties of WC-8Ni cemented carbide produced by vacuum sintering

The WC-8Ni powder was prepared by the ball milling method, then consolidated via a vacuum sintering technique. The influence of sintering temperature varying from 1375 °C up to 1500 °C on microstructure and mechanical properties of WC-8Ni cemented carbide was investigated. The best mechanical properties of the samples have been achieved at sintering temperature of 1450 °C. At which the relative density, hardness and fracture toughness (K_IC) of the samples are 99.81%, 13.23 GPa and 24.22 MPa m^1/2, respectively. The effect of η-phase identified by Murakami etching method and XRD technique on the mechanical properties was also discussed.     

Effect of phase transformation of CoCrFeNiAl high-entropy alloy on mechanical properties of WC-CoCrFeNiAl composites

WC-CoCrFeNiAl composites were fabricated via SPS using commercial CoCrFeNiAl and WC powders, with the optimal addition content of CoCrFeNiAl determined. Furthermore, the influence of phase transformation in CoCrFeNiAl high-entropy alloy on the mechanical properties of WC-CoCrFeNiAl composites was investigated. The results indicate that the hysteresis diffusion effect of CoCrFeNiAl HEA can significantly impede the growth of WC grains. Moreover, during the sintering process, a BCC-to-FCC phase transformation occurs in CoCrFeNiAl HEA. The phase transition of HEA can be regulated by adjusting the sintering temperature, resulting in a decrease in hardness and an increase in fracture toughness of WC-CoCrFeNiAl composites as HEAs undergo phase transformation. The Vickers hardness and fracture toughness values of WC-10CoCrFeNiAl composites sintered at 1250 °C are comparable to those of WC-10Co hard alloy, with respective values of 17.64 GPa and 12.3 MPa m^1/2.     

Mechanical and tribological properties of SiC whisker-reinforced SiC composites via oscillatory pressure sintering

SiC whisker (SiCw)-reinforced SiC composites were prepared by an oscillatory pressure sintering (OPS) process, and the effects of SiCw content on the microstructure and mechanical and tribological properties of such composites were investigated. The addition of SiCw could promote the formation of long columnar α-SiC, and the aspect ratio of α-SiC grains first increased and then decreased with the increase of SiCw content. When the SiCw content was 5.42 wt%, the relative density of the SiC–SiCw composite reached up to 99.45%. The SiC–5.42 wt% SiCw composite possessed the highest Vickers hardness, fracture toughness, and flexural strength of 30.68 GPa, 6.66 MPa·m^1/2, and 733 MPa, respectively. In addition, the SiC–5.42 wt% SiCw composite exhibited the excellent wear resistance when rubbed with GCr15 steel balls, with a friction coefficient of .76 and a wear rate of 4.12 × 10⁻⁷ mm³·N⁻¹·m⁻¹. This could be ascribed to the improved mechanical properties of SiC–SiCw composites, which enhanced the ability to resist peeling and micro-cutting, thereby enhancing the tribological properties of the composites.     

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.     

Preparation and toughening mechanism of Mo2NiB2-based cermets with SiC whiskers

Mo₂NiB₂ is a kind of cermet with excellent mechanical properties, stable chemical properties, and excellent corrosion resistance and is often used in wear-resistant application fields, such as injection molding machine parts, can making tools and hot copper extruding dies. The brittleness of Mo₂NiB₂-based cermets limits their wide application. Mo₂NiB₂-based cermets were prepared by the vacuum sintering method, the effect of SiC whiskers (SiCw) on the microstructure and mechanical properties of cermets was investigated, and the toughening mechanism of SiCw on cermets was further discussed. The results indicate that with increasing SiCw content, the indentation fracture toughness (K_IC), transverse fracture strength (TRS), and Vickers hardness (HV) of the cermets first increase and then decrease. The HV, TRS, and indentation fracture toughness of Mo₂NiB₂-based cermets with 0.5 wt% SiCw are 1 113 HV, 1 620 MPa, and 27.97 MPa·m^1/2, respectively, which are 16.8%, 22.7%, and 25% higher than those without SiCw. In the sliding friction tests, Mo₂NiB₂-based cermets with 0.5 wt% SiCw have the smallest friction coefficient, low wear rate, and high wear resistance. SEM observation and analysis of the crack path and fracture surface showed that the toughening mechanism is whisker bridging, crack deflection, microcrack toughening, and whisker pull-out. The results indicate that the addition of 0.5 wt% SiCw can effectively improve the mechanical properties of Mo₂NiB₂-based cermets and further expand the application space of Mo₂NiB₂-based cermets.     

Sintering behaviour of alumina–niobium carbide composites

Ceramic cutting tools have been developed as a technological alternative to cemented carbides in order to improve cutting speeds and productivity. Al₂O₃ reinforced with refractory carbides improve fracture toughness and hardness to values appropriate for cutting applications. Al₂O₃–NbC composites were either pressureless sintered or hot-pressed without sintering additives. NbC contents ranged from 5 to 30 wt%. Particle dispersion limited the grain growth of Al₂O₃ as a result of the pinning effect. Pressureless sintering resulted in hardness values of approximately 13 GPa and fracture toughness around 3.6 MPa m^1/2. Hot-pressing improved both hardness and fracture toughness of the material to 19.7 GPa and 4.5 MPa m^1/2, respectively.     

The influence of different SiC amounts on the microstructure,densification, and mechanical properties of hot-pressed Al2O3-SiC composites

The hot pressing process of monolithic Al₂O₃ and Al₂O₃-SiC composites with 0-25 wt% of submicrometer silicon carbide was done in this paper. The presence of SiC particles prohibited the grain growth of the Al₂O₃ matrix during sintering at the temperatures of 1450°C and 1550°C for 1 h and under the pressure of 30 MPa in vacuum. The effect of SiC reinforcement on the mechanical properties of composite specimens like fracture toughness, flexural strength, and hardness was discussed. The results showed that the maximum values of fracture toughness (5.9 ± 0.5 MPa.m^1/2) and hardness (20.8 ± 0.4 GPa) were obtained for the Al₂O₃-5 wt% SiC composite specimens. The significant improvement in fracture toughness of composite specimens in comparison with the monolithic alumina (3.1 ± 0.4 MPa.m^1/2) could be attributed to crack deflection as one of the toughening mechanisms with regard to the presence of SiC particles. In addition, the flexural strength was improved by increasing SiC value up to 25 wt% and reached 395 ± 1.4 MPa. The scanning electron microscopy (SEM) observations verified that the increasing of flexural strength was related to the fine-grained microstructure.     

Static and dynamic mechanical properties of boron carbide processed by spark plasma sintering

Spark plasma sintering (SPS) has become a popular technique for the densification of covalent ceramics. The present investigation is focused on the static mechanical properties and dynamic compressive behavior of SPS consolidated boron carbide powder without any sintering additives. Fully dense boron carbide bodies were obtained by a short high temperature SPS treatment. The mechanical properties of the SPS-processed material, namely hardness (32 GPa), Young modulus (470 GPa), fracture toughness K_C (3.9–4.9 MPa m^0.5), flexural strength (430 MPa) and Hugoniot elastic limit (17–19 GPa) are close or even better than those of hot-pressed boron carbide.