The WC-Co cemented carbides with 4 wt%~14 wt% Co content were fabricated by spark plasma sintering. The effect of Co content on microstructure and mechanical properties of WC-Co cemented carbide were ...analyzed. The results showed that the grain size of cemented carbide with different Co content was in 220–380 nm. As the Co content increased, the density, fracture toughness and flexural strength of cemented carbide increased, but the hardness gradually decreased. The hardness decreased by approximately 1.6 GPa with per 2 wt% increase of the Co content when the Co content was below 10 wt%. The optimal comprehensive mechanical properties was optimal when Co content was 8 wt%. The hardness, fracture toughness, and flexural strength were 19.87 GPa, 12.27 MPa m1/2 and 1834 MPa, respectively. The cemented carbide fabricated in this paper are more excellent compared to the commercial cemented carbides.
It is crucial to design a novel active filler metal for brazing WC–Co cemented carbide–steel joints at low temperatures. In this study, we designed a low-melting-point multi-component active filler ...metal (Ag–Cu–Sn–Ti) based on Ag–Cu–Ti filler metal to achieve perfect combination of WC–Co/40Cr steel joints. The interfacial microstructure of the WC–Co/40Cr steel joint was comprehensively characterized, and the joint-bonding mechanism, mechanical properties, and fracture behavior after brazing at 700–780 °C were systematically analyzed. On both sides of the filler metal, WC and α-Fe combined with the TiC layer, enhancing the bonding of the filler metal to base materials. The typical structure of the joint is WC–Co/TiC layer/Co2SnTi + Cu–doped Cu81Sn22 + Ag s, s + Ti–Cu granules/TiC layer/40Cr. The maximum shear strength of 241 MPa was obtained when the joint was brazed at 740 °C for 10 min, which is approximately 50% higher than those of previous low-temperature vacuum-brazed WC–Co/steel joints. The main factors leading to premature failure of joint include the distribution of phases in filler metal layer and defects of WC–Co caused by Co diffusion.
•Designed a novel multicomponent active filler metal for application.•The microstructure of the WC–Co/Ag–Cu–Sn–Ti/40Cr joint was characterized and the connection mechanism was analyzed.•On both sides of the filler layer, WC and α-Fe combined with the TiC reaction layer.•The cost of filler metal is reduced and the shear strength of WC–Co/steel joint with low-temperature brazing is improved.
Assembly and packaging technology is one of the most critical factors that restrict the development of microelectromechanical systems (MEMS), including chips and other devices. Dispensing robot is a ...key high-end equipment in MEMS packaging. Its core component, WC-Co impact needle, is limited by fretting wear and deformation, leading to reduced service accuracy and life, which is the most important cause of failure. Impact fretting wear frequently occurs in micro-nano mechanical systems and has been widely studied. However, the combined high frequency (∼300 HZ) and micro impact amplitude (∼120 μm) wear behaviors such as WC-Co impact needle with ultrafine grain (∼100 nm) is rarely concerned. To further understand the influence of impact frequency and impact velocity on the wear rate of impact needle, dispensing experiments were designed and the wear mechanism was investigated. Results indicated that the impact velocity has more influence on the wear rate of impact needle than the impact frequency. In addition, a high-current pulsed electron beam (HCPEB) surface treatment method which can effectively increase the wear resistance of impact needle was proposed. After HCPEB treatment, the abrasion loss was reduced by 44% compared to the untreated one at the same impact frequency and different impact velocities, while the abrasion loss was reduced by 52% compared to the untreated one at the same impact velocity and different frequencies. These can be attributed to the fact that HCPEB treatment decreased the grain size of WC-Co cemented carbide impact needle and promoted WC phase transition, leading to an increase in microhardness.
•High-current pulsed electron beam (HCPEB) was employed to WC-Co impact needle.•Impact velocity has a significant effect on impact fretting wear resistance of impact needle than impact frequency.•The microhardness of HCPEB treated impact needle being 1.4 times compared to untreated one.•Impact wear resistance improvement attributed to the WC phase transition and surface grain refinement.
The WC-6Co cemented carbides were sintered using hot oscillating pressing (HOP) method. The interplay of sintering parameters between microstructure and mechanical properties were systematically ...investigated. Results revealed that HOP could enhance the densification, restrain grain growth, shorten Co matrix average free path, and accelerate Co distribution in WC-6Co cemented carbides, which improved the combined performance for hardness of 25.22 Gpa and fracture toughness of 12.89 MPa m1/2 after sintering at 1400 °C. It is worth emphasizing that these mechanical properties are better than similar cemented carbides prepared by conventional methods, indicating the promise of utilizing HOP for high-performance cemented carbides.
Friction and wear properties of WC–Co cemented carbides with Co concentrations ranging from 6 up to 12
wt% and WC grain sizes in the sub-micrometer scale have been examined in reciprocating sliding ...wear experiments using a high-frequency TE77 pin-on-plate system. The aim of the work was to investigate the influence of test parameters such as normal contact force, oscillating velocity and sliding distance on the tribological characteristics. The tests were carried out under unlubricated conditions. The generated wear was quantified volumetrically by means of surface topography scanning measurements. The changes in test parameters gave a variation in wear of more than one order of magnitude. A marked increase in wear was seen as the load increased, whereas the friction coefficient displayed an opposite trend. Raising the oscillating speed was found to increase both friction coefficient and wear level. The wear tracks and wear debris were analyzed by scanning electron microscopy (SEM), energy disperse X-ray spectrometry (EDX) and X-ray diffraction (XRD). The observed mechanisms of wear are discussed with respect to the magnitude of wear that was measured.
The binder phase Co in WC‐Co cemented carbide is dissolved easily in corrosive media (even in neutral solution), which has limited its application in a wider range. In this paper, the influence of Cr ...on corrosion resistance of WC‐Co immersed in neutral solution was studied, with a focus on the surface chemistry of the corrosion product. The results show that in neutral solution, the corrosion is mainly caused by the selective dissolution of Co and the dominant surface corrosion product after immersion is Co (OH)2. The corrosion resistance of WC‐Co cemented carbide can be improved by the addition of Cr. This can be explained by the formation of more protective chromium containing oxide on the binder phase of WC‐Co‐Cr alloy, leading to reduced corrosion rate.
Based on wet chemical precipitation and spray drying technology, a Y–Zr-doped W powder was prepared as a precursor material for the preparation of Y–Zr-modified WC-8Co cemented carbides. The ...Y–Zr-modified WC-8Co hard alloy prepared by low pressure sintering method was used to study the change in the interface structure between the second phase and the substrate. The result showed that in the Y–Zr-doped W powder, the second phase was Y2O3 and ZrO2 particles. The Y2O3 particles had a coherent interface with the W matrix, which was the reason for the formation of intragranular nano second phases in the modified hard alloys. The interface between ZrO2 and W particles exhibited a semi coherent relationship, which was consistent with the interface structure of WC crystals and the second phase at grain boundaries. Some free second phase particles Y2O3 and ZrO2 in the doped powder formed a staggered interface structure in the modified alloy, generating Y–Zr–O solid solutions dispersed in the bonding phase. The performance of Y–Zr-modified WC-8Co hard alloy were superior to pure WC-8Co alloy prepared by the same process. The stable and compatible interface structure between WC grains and the second phase was an effective means to improve the performance of modified WC-8Co cemented carbide.
This article is to devoted to investigate the effect of graphene oxide (GO) on the mechanical and tribological properties on WC-Co cemented carbide. Based on the microstructure and morphology of wear ...surface, it is found that the addition of GO has little effect on the densification process and the grain size of cemented carbide, thus hardly weakening the hardness, while the fracture toughness has been improved 29.1%. Both friction coefficient and specific wear rate have been significantly decreased due to the added GO. The bridging mechanism caused by GO is considered to be the main reason for the toughening effect in cemented carbide. Increasing fracture toughness by the added GO during sintering is noticed to significantly enhance the anti-wear performance of WC-Co cemented carbide. The effect of fracture toughness on wear resistance should be attributed to the added GO preventing the cobalt binder phase from occurring the combination of plastic deformation and micro-abrasion, and hindering the crack propagation of WC grains during sliding.
•The mechanical and tribological properties of WC-Co composites are improved due to the addition of graphene oxide.•The bridging mechanism caused by graphene oxide is the main reason for the toughening effect in cemented carbide.•Increasing fracture toughness by the added graphene oxide enhances the anti-wear performance of WC-Co cemented carbide.•The plastic deformation, micro-abrasion and crack propagation are hindered due to graphene oxide during sliding.
WC–Co cemented carbide/steel brazed at low–temperature is of significant scientific and technical interest. In this study, the interface microstructure between the filler alloy and WC–Co and 40Cr ...steel, the formation process of the joint microstructure, and the effect of brazing temperature on the microstructure and properties of joints were systematically studied. The filler alloy was bonded by forming a TiC reaction layer with WC–Co and 40Cr steel, which enhanced the retention of the filler layer on the joint. The microstructure of the joint was a WC–Co/TiC reaction layer/TiCo reaction layer/Cu2InTi + eutectic structure (Ag s, s + Ag–doped Cu7In3 + Cu4In) + Cu s, s/TiC reaction layer/40Cr steel. Moreover, the maximum average shear strength of the joint (brazed at 740 °C) reached 258 MPa, which is approximately 60% higher than those reported in the literature. The fracture behavior of the joint was mainly affected by the distribution of the Cu2InTi intermetallic compounds in the filler layer and the diffusion of Co from the cemented carbide.
•WC–Co cemented carbide and 40Cr steel was brazed at low–temperature (700–780 °C) with Ag–Cu–In–Ti filler alloy.•TiC reaction layer was formed at the interfaces of WC–Co/filler alloy and 40Cr steel/filler alloy after brazed, ensuring the perfect combination of the interface.•The maximum average shear strength of the joints (brazed at 740 °C) can reach 258 MPa, which is enhanced approximately 60%.•The joint dependence of fracture behaviors on joint microstructures was clarified.
