Microstructure And Wear Properties Of WC-Ni-Co/Stainless Steel Micro Drilling Composites

With the development of information technology in China,the use of micro-drills for processing PCB boards in information industry is increasing.The traditional materials used to manufacture micro-drill bits are mostly tungsten carbide(WC)or single high-speed steel,which is widely used in information industry.WC has good hardness and other excellent properties,but its toughness is poor,and brittle fracture easily occurs in the process of use,and the cost of cemented carbide is higher,but there is a certain gap between hardness and wear resistance of high speed steel and WC.Therefore,in this paper,WC-Ni-Co/stainless steel micro-drilling composites were prepared by combining powder and solid by vacuum sintering and cold pressing.The influence of different sintering temperature and holding time on WC-Ni-was studied by using optical microscope(OM),scanning electron microscope(SEM),energy dispersive spectrometer(EDS),X-ray diffraction analyzer(XRD),friction and wear tester and Vickers hardness tester.The main research results are as follows:(1)The effects of different sintering temperatures on the microstructure,hardness and wear resistance of WC-Ni-Co/stainless steel micro-drilling composites were studied.The results show that the number of micro-gaps in WC-Ni-Co structure decreases with the increase of sintering temperature.When the sintering temperature is 1320?,the density reaches the best 86.40%.At this time,there are few defects at the interface of the composite material,and the interface bonding layer is relatively flat,indicating that the interface bonding degree is better.At this sintering temperature,the average hardness of WC-Ni-Co side reaches 1501HV_0.1,and the wear amount of WC-Ni-Co/stainless steel composite is smaller,and its wear resistance is the best.(2)The effects of different sintering temperatures on element diffusion at the interface of WC-Ni-Co/stainless steel micro-drilling composites were analyzed.The results show that increasing sintering temperature is beneficial to the occurrence of element diffusion.When the sintering temperature reaches 1320?,the diffusion phenomenon of Fe,Cr,Co and Ni occurs obviously,and the diffusion of W also occurs to a certain extent.At this sintering temperature,the stainless steel matrix reacts with WC-Ni-Co reinforcement to form new phases such as Cr₄Ni₁₅W,Co Cx and Fe₃C.(3)The effects of holding time on microstructure and hardness of WC-Ni-Co/stainless steel micro-drilling composites were studied.The results show that with the increase of holding time,the density of WC-Ni-Co side structure becomes higher and higher.When the holding time is 120min,the density of WC-Ni-Co side structure reaches 89.01%,and the hardness of the structure reaches the highest 1500HV_0.1.With the increase of holding time,the interfacial bonding layer produced by the mutual diffusion of alloy elements becomes better and better.With the increase of holding time,the four elements Fe,Cr,Co and Ni diffuse obviously,and the W element also diffuses to a certain extent.When the holding time is 90min,WC-Ni-Co is metallurgically bonded with the base stainless steel,and new phases such as Fe₇W₆and Cr₂Fe₁₄C are formed.(4)The effect of holding time on wear resistance of WC-Ni-Co/stainless steel micro-drilling composites was discussed.The results show that with the increase of holding time,the wear resistance of the composites has been significantly improved.When the holding time is 120min,the wear amount is the least,and the wear resistance of the composite material is the best.