Wear resistance of nanostructured Cr-based WC hardmetals sintered by spark plasma sintering

Nanostructured Cr-based WC hardmetals are successfully sintered by spark plasma sintering. The wear behaviour of these Cr-based WC hardmetals with different C contents ranging from 5.57 wt% to 6.91 wt%, is evaluated performing sliding wear tests under two different wear conditions. This work analyses the influence of the C content on the wear performance through the study of the phase formation and WC grain size. The Cr-based hardmetal with 5.57 wt% C content exhibits a lower wear rate than Co-based WC hardmetals tested under similar dry ball-on-plate wear conditions, even considering that these Co-based WC hardmetals have higher WC content (90 wt%) than Cr-based WC hardmetals (83.2 wt%). The combination of a nanosized WC grain and the avoidance of brittle (Cr,Fe)₇C₃ or soft graphite phases leads to a superior wear performance. Thus, the use of Cr-based binders in the hardmetal industry, alternatively to Co-based binders, is promising in applications in which high wear resistance is needed.     

Ultra high-pressure spark plasma sintered ZrC-Mo and ZrC-TiC composites

Ultra-high-pressure spark plasma sintering was applied to ZrC-20 wt%Mo and ZrC-20 wt%TiC composites with a pressure up to 7.8 GPa and temperatures of 1550 °C and 1950 °C. Mechanical performance of the composites was benchmarked against a plain ZrC produced by the same method. Both composites outperformed the pure ZrC with superior hardness and indentation fracture toughness of 2239 HV1 and 5.4 MPa m^1/2, and 1896 HV1 and 5.9 MPa m^1/2, respectively, for ZrC-Mo and ZrC-TiC composites. It was shown that ultra-high compaction pressure affected the ZrC-20 wt%TiC miscibility gap by lowering the temperature threshold from the usually applied 1800 °C down to 1550 °C resulting in formation of the solid state solution of (Zr,Ti)C. In contrast, the high pressure does not inhibit the carburisation of Mo with ZrC to form MoC, even when experiments were performed in a graphite free environment. The equiaxed morphology of ZrC grains along with a right-shift in XRD peaks for ZrC indicates dissolution of Mo in ZrC resulting in formation of the solid solution of (Zr,Mo)C. High-temperature X-ray diffraction analysis under oxidation conditions was performed on the samples showing degradation of ZrC-20 wt%Mo due to the oxidation of Mo at high-temperature leading to MoO₃ vaporisation. Conversely, the oxidation of ZrC-20 wt%TiC composites was characterised by formation of ZrO₂ and TiO₂ remaining stable up to 1500 °C.     

Effects of WC particle size on densification and properties of spark plasma sintered WC–Co cermet

The WC–Co cermet bulks were prepared by spark plasma sintering (SPS) using powder mixtures with different-scaled WC particles. The SPS densification process was studied by calculating the current distribution between the powder sample and the die in the SPS system. The microstructures were characterized and compared for different samples by the WC grain size, Co mean free path and contiguity of WC grains. In spite of a weak effect of WC particle size on the SPS densification stages, the WC particle size plays a significant role in the homogeneity of the cermet microstructure. Good mechanical properties of the SPSed cermet were obtained with an optimized WC and Co particle-size combination. The effects of scale combination of WC and Co particles on the microstructure hence the properties of the SPSed cermet were discussed.     

火花等离子烧结技术制备的WC/Co纳米硬质合金

研究了火花等离子烧结工艺与YG10、YG12两种纳米硬质合金性能的关系.然后采用火花等离子烧结技术制备了硬质合金功能梯度材料,该材料由纳米WC/10%Co、纳米WC/12%Co、微米WC/15%Co混合粉以及不锈钢圆片烧结而成.显微硬度压痕显示该材料各层间的应力较小.     

Study of characteristics and properties of spark plasma sintered WC with the use of alternative Fe-Ni-Nb binder as Co replacement

Most of all WC-based cemented carbides use cobalt as binder due to the excellent strength and ductility that this combination provides. Motivators to find alternative binders have been related to factors such as the shortage and price oscillations of the cobalt and toxicity of the WC-Co system. In this work, Fe-Ni-Nb was used as alternative binder for WC sintered via spark plasma sintering (SPS) technique. The composites were sintered at different sintering temperatures (1100 °C, 1200 °C and 1300 °C). In addition, WC-Co was sintered at 1200 °C via SPS for comparison purposes. X-ray diffraction and Scanning electron microscopy (SEM) were employed as characterization methods to investigate the crystalline phase's formation, sintering effectiveness, porosity and phase distribution. Mechanical properties such as Vickers hardness, fracture toughness, nanohardness, elastic modulus and thermal properties (thermal expansion coefficient) were evaluated. The results demonstrate Fe-Ni-Nb as a viable alternative binder to cobalt in hardmetal applications.     

Microstructure of the cBN/WC6Co composite produced by the pulse plasma sintering (PPS) method

The cBN/WC6Co composite with the relative density of 99.8% and hardness of 2130 HV5 was produced by sintering at a temperature of 1150 °C under a pressure of 100 MPa for 5 min. The composite was sintered using electric pulses generated periodically by discharging a capacitor battery. The constituent phases of the composite, as identified by the NBED method, were the cBN, WC, and Co phases. The HR STEM observations have shown that the interfaces between the individual phases are continuous and no pores or precipitates of other phases can be seen there. Thanks to the specific heating realized by electric pulses, the composite is heated during each current pulse to a temperature of 1950 °C at a rate of 10⁵ °C/s. As a result of these quick changes of the temperature, transient thermal compressive stresses of about 3 GPa are induced in the composite, which results in the grains of the WC composite matrix being refined and defected.     

The effect of volume fraction of WC particles on wear behavior of in-situ WC/Fe composites by spark plasma sintering

Tungsten carbide (WC) particles have been in-situ synthesized through the reaction between tungsten particles and carbide particles by spark plasma sintering (SPS). The composites with different WC content were comparatively observed by the techniques of scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM), X-ray diffraction, hardness and pin-to-disc abrasive wear test. The results showed that the formed WC particles were homogenously distributed in the iron matrix with the size of smaller than 25 μm. Additionally, with the increasing of the WC content, the hardness of composites, the microhardness of matrix and the wear resistance increased, but there was no change significantly between 32 vol% WC/Fe composites and 42 vol% WC/Fe composites. The composites possessed excellent wear resistance comparing the specific wear rate determined in the present work to the martensitic wear-resistant steel under the load of 80 N after a sliding distance of ~ 950 m. The specific wear rate of the martensitic wear-resistant steel was a factor of 24 and 48 times higher than WC/Fe composites, when the content of WC was 32 vol% and 42 vol% in WC/Fe composites, respectively. The main wear mechanism was synthetic of abrasion wear and oxidation wear. The wear performance of 32 vol% WC/Fe composites didn't appear to be much different from 42 vol% WC/Fe composites, due to the WC particles in the 42 vol% composites produced stress concentration easily, which could ultimately induce the creak initiation around WC particles in the subsurface (near wear surface) and propagation to wear surface promoting the breakup of surface film.     

碳化钨含量对钴基碳化钨复合喷熔层耐磨性的影响

为提高20钢的耐磨料磨损性能,利用氧一乙炔火焰喷涂的方法制备了不同WC含量的钴基WC复合喷熔层。显微组织分析表明,复合喷熔层与基体结合良好,喷熔层内WC颗粒分布均匀。磨损试验结果表明,钴基WC复合喷熔层具有优异的耐磨性能,随WC含量的增加,喷熔层耐磨性能增强。     

Wear resistance and thermal stability enhancement of PDC sintered with Ti-coated diamond and cBN

Ti-coated diamond with different particle sizes and proper amounts of cubic boron nitride (cBN) was used to fabricate polycrystalline diamond composite (PDC) with improved wear resistance and thermal stability under high temperature and high pressure (5.5–6.5GPa, 1500–1650 °C). The ratio of Ti-coated diamond powder, cBN powder and normal diamond powder was W_30–50: W_4–8: W_0–1 = 70: 15: 15. Cobalt (Co) was used as a binder, and cemented tungsten carbide was used as a substrate to sinter a new high-performance PDC. Ti and TiC on the surface of Ti-coated diamond reacted with cBN under high temperature and high pressure to generate new ceramic phases such as TiB₂, TiN and TiN_0.3, which have high hardness and good wear resistance. Compared with the conventional PDC, the impact toughness and wear resistance of PDC with Ti-coated diamond and cBN addition were enhanced by 19% and 28%, respectively. The ceramic phase acts as a protective barrier, which enhances the initial graphitization and oxidizing temperature to 942–950 °C, which were 162–170 °C higher than the conventional PDC. The new ceramic barrier wrapped around the surface of the diamond and Co after the formation of the D-D (diamond-diamond) bonding will give priority to the oxidation reaction of Co and diamond with oxygen, which prohibits cobalt-catalytic graphitization of diamond, meeting the needs of PDC thermal stability and wear resistance in the field of drilling.     

Pulsed electric current sintered Fe3Al bonded WC composites

WC based composites with 5, 10 and 20 vol.% Fe₃Al binder were consolidated via pulsed electric current sintering (PECS) in the solid state for 4 min at 1200 °C under a pressure of 90 MPa. Microstructural analysis revealed a homogeneous Fe₃Al binder distribution, ultrafine WC grains and dispersed Al₂O₃ particle clusters. The WC-5 vol.% Fe₃Al composite combines an excellent Vickers hardness of 25.6 GPa with very high Young’s modulus of 693 GPa, a fracture toughness of 7.6 MPa m^1/2 and flexural strength of 1000 MPa. With increasing Fe₃Al binder content, the hardness and stiffness decreased linearly to 19.9 and 539 GPa, respectively with increasing binder content up to 20 vol.%, while the fracture toughness and flexural strength were hardly influenced by the binder content. Compared to WC–Co cemented carbides processed under exactly the same conditions, the WC–Fe₃Al composites exhibit a substantially higher hardness and Young’s modulus.     

等离子喷涂WC—Co涂层的磨料磨损

采用等离子喷涂方法在真空和大气环境下喷涂制备了不同Ｃｏ基含量的ＷＣ－Ｃｏ涂层，用橡胶轮磨损试验机进行高应力和低应力磨料磨损试验，并对涂层的相结构及磨损机理进行了研究，结果表明：真空喷涂涂层的耐磨性明显优于大气中喷涂涂层的耐磨性，涂层的耐磨性主要取决于涂层的致密程度和涂层中的相，而与涂层硬度的关系不是太大，等离子喷涂ＷＣ－Ｃｏ涂层的磨损机理是在低应力磨料磨损情况下硬度低的富Ｃｏ区先磨损，硬度高的ＷＣ     

Hydrogen storage performance of Mg-based composites prepared by spark plasma sintering

The hydrogen storage capacities, hydrogen absorption mechanism and hydride stability of Mg-based composites prepared by spark plasma sintering (SPS) were investigated in this paper. The results showed that the composites had a double-phase microstructure of Mg phase and V-based solid solution, with nanocrystalline magnesium existing at their sintering interface. With the addition of the V-based solid solution in 20% volume fraction, the composite exhibited a maximum reversible hydrogen storage capacity of 4.2 wt.% at 573 K, compared with that of pure Mg of almost zero. DSC results indicated that the hydride decomposition temperature of MgH₂ decreased sharply from 708 K in pure Mg to 636 K and to 591 K as the volume of V-based solid solution increased from 20 vol.% to 50 vol.%. With the addition of V-based solid solution, the hydrogen absorption kinetics of pure Mg was greatly improved at 573 K, and its hydrogen absorption mechanism changed from surface reaction control to diffusion control in the composite. Based on these experimental results, a model was put forward to describe the hydrogen absorption/desorption mechanism in these composites.     

等离子喷涂WC复合涂层耐磨性能

利用大气等离子喷涂技术在45钢基体上制备了WC复合涂层,采用Ml-10摩擦磨损试验机研究了涂层在干摩擦条件下摩擦磨损性能.结果表明:涂层比基体耐磨性高很多,未出现硬质相的剥落;涂层具有典型的"软基体加硬质相"耐磨组织结构,Ni包Al粉末的加入强化了软相,涂层在干摩擦条件下表现出来比较优良的耐磨性;由于气孔不可避免存在于涂层,涂层磨痕在气孔处出现断裂和塌陷现象,因此提高涂层致密性能降低涂层磨损率.     

高速火焰与等离子喷涂WC／Co涂层的性能比较

分析比较了超音速喷涂与等离子体喷涂的ＷＣ／Ｃｏ涂层的形貌,显微组织结构,孔隙率,硬度及其耐磨性,结果表明超音速火焰喷涂的ＷＣ／Ｃｏ涂层具有与粉末相近的相结构,也说ＷＣ颗粒在超音速火焰喷涂过程中,只有极少部分被分解和氧化,同时涂层具有很高的致密度,硬度和良好的耐磨性,涂层与基体的结合情况也得到很大的改善。     

纳米稀土改性热喷涂WC/12Co涂层的摩擦磨损性能研究

利用超音速火焰喷涂技术在45#钢表面制备了不同稀土含量的WC/12Co涂层.在HV-5型小负荷维氏硬度计上测定了涂层的显微硬度,在WTM-2E微型摩擦磨损试验仪上测定了涂层的摩擦磨损性能.结果表明:适量稀土的加入使WC/12Co涂层的显微硬度提高,耐磨性增强.当稀土含量在1.5%时,涂层的硬度提高42%,磨损体积最小.     

M42/45钢双金属复合材料的SPS烧结及其界面研究

利用放电等离子烧结技术（SPS）实现了M42粉末高速钢的制备及与45钢的连接,对其界面的显微组织形貌、元素分布、显微硬度及相界面形成过程进行了测试分析。结果表明,接头过渡层的成分、显微硬度都呈现梯度变化,连接界面没有裂纹及大孔洞出现,界面结合紧密,其过渡层厚度可达10.2μm;界面连接为熔合连接与扩散连接的共同作用,其中烧结初期以熔合连接为主,烧结中后期,扩散连接逐渐成为主导。     

Sintering of WC-Co powder with nanocrystalline WC by spark plasma sintering

A 92WC-8Co powder mixture with 33 nm WC grains was prepared by strengthening ball milling and was then sintered by spark plasma sintering （SPS） at 1000-1200℃ for 5-18 rain under 10-25 kN, respectively. Movement of the position of low punch shown shrinkage of the sintered body began above 800℃. The shrinkage slowly rose as the temperature rose from 800 to 1000℃ and then quickly rose at above 1000℃ and then gradually rose at above 1150℃. The densities of the samples increased with an increase in sintering temperature, rapidly below 1100℃, and then gradually above 1100℃. WC grains grow gradually with increasing sintering temperature. The powder was sintered to near full density at 1100℃ for 5 rain under 10 kN. The best result of the sample with 275 nm WC grains and no pores was obtained at 1150℃ under 10 kN for 5 rain. The research found the graphite die had a function of carburization, which could compensate the sintered body for the lack of carbon, and had the normal microstructure.     

Wear resistance of Zr/WC composite coatings on Cr12MoV steel surface by electric spark deposition

Zr/WC composite coating was prepared on the surface of Cr12MoV steel by electric spark deposition technology to change its surface properties. The surface and worn surface morphology of the coating were observed using scanning electron microscope. Dry friction and wear tests of the coatings were carried out at room temperature. The results show that the coating is continuous and uniform, and the thickness was about 50-60 μm. The microhardness of the coating surface was highest at 1140 HV_(200g), which was significantly higher than that of the substrate. The ear tests results show that the wear weight loss, wear volume and wear rate follow the following rules: Cr12MoVWC coating Zr/WC composite coating.     

Microstructure and wear behavior of spark plasma sintering sintered Al2O3/WC-based composite

Various alumina/tungsten carbide based nanocomposites have been fabricated by spark plasma sintering and their wear properties have been investigated by performing ball-on-disk type wear test at room temperature under ambient environment. Our results reveal that the main facture behavior of the Al₂O₃/tungsten carbide composites sliding against Al₂O₃ balls is the plastic deformation. Crack formation and grain pull-out in the wear processes are responsible for lowering the wear rate. The Vickers hardness and toughness values are directly related to wear behavior of the composites that grounds Al₂O₃/WC to show lower wear rate on smoothly worn surface.