In-situ Synthesis Of W(WC) Composite Grain And Study On Infiltration Preparation Technology Of 75W-25Cu Composite

As a special composite(also called"pseudo-alloy"),W-Cu composites can meet the requirements of high-voltage electrical contact materials,such as low resistance,high thermal conductivity,high melting point,high strength at room temperature and high temperature,high hardness,good plastic toughness,arc ablation resistance and good manufacturing performance,etc.However,W-Cu composites prepared by traditional process has been unable to meet the extremely requirements of electrical properties,wear resistance and high-temperature strength.This is a feasible way to improve the high-temperature performance and wear resistance of W-Cu composites by adding various refractory,high-temperature resistant,and high strength doping materials,such as rare earth and its oxides,ceramic particles.In this paper,the in-situ synthesis of WC and the preparation technology of W-Cu composites were studied in combination with the problems existed in the preparation process of WC doped reinforced W-Cu composites and the mainstream production technology.Taking 75W-25Cu as an example,the effects of different binder systems and multi-component binder systems on the in-situ synthesis of WC in W-Cu composites fabricated infiltration were studied.The effects of pulverizing method,infiltration sintering process and process control on the microstructure and properties of W-Cu composites were discussed.The wear resistance and high temperature compressive strength of traditional W-Cu composites and WC reinforced W-Cu composites prepared in this study were compared.The main research contents and results of this paper are as follows:(1)The effects of different binder systems on the in-situ synthesis of WC in W skeleton were studied.Firstly,the W powders with 1.5 wt.%paraffin,1.5 wt.%rubber solution,1.5 wt.%stearic acid,and 1.5 wt.%self-made adhesive was molded to obtain W green compacts.Then,the W skeleton was fabricated by degreasing and skeleton pre-sintering.The results of microstructure and XRD analysis show that only self-made adhesive can be simultaneous as binder and carbon source for W carbonization.Combined with the TG-DTA curves of four binders and thermodynamic calculation of the W carbonization process,the formation of WC was analyzed and discussed.It is considered that the coated on the surface of W particles formed by self-made adhesive was creates conditions for the uniform distribution of carbon sources,and the influence for W carbonization on the conductivity of composites due to the formation of W₂C phase was reduced.At the same time,the influence of self-made adhesive content on the microstructure and properties of WC reinforced W-Cu composites was studied by using the two-component binder system(self-made adhesive with stearic acid)on the premise of ensuring green compact formability.The results show that with the increase of self-made adhesive content,the conductivity of the composites first increases and then decreases,the hardness increases linearly;the relative density first increased and then stabilized.(2)Combined with the traditional production process,the milling process,sintering process,and the control of infiltration sintering process for WC reinforced W-Cu composites was optimized and adjusted.Due to the material of ball milling tank and ball,excessive impurities will be introduced after long-term ball milling,which can not guarantee the density and conductivity of composite materials at the same time.It can avoid the introduction of excessive impurities by using V-type mixer to make powders,and the density and conductivity of composites were improved.The best sintering process after studied the different sintering temperature,holding time,and cooling rate was obtained as follows:increasing to 1150?at a rate of 5?/min?holding for 60 min?increasing to 1300?at a rate of 3?/min?holding for 90 min?cooling with the furnace.The sintering process control of different profiles was optimized and adjusted through bidirectional infiltration and alumina powder coating to control the seepage direction of Cu liquid in infiltration sintering process.(3)The conventional properties(hardness,conductivity,relative density),wear resistance and compressive strength of traditional W-Cu composites and WC reinforced W-Cu composites prepared under the same infiltration process were comprehensively evaluated.With the increase of self-made adhesive content,the conductivity and relative density of the composites first increased and then decreased,and the hardness increased linearly.The average friction coefficient(0.58)and mass loss(0.31 g)of carbonized WC-Cu composites 1 wt.%self-made adhesive were lower than those of conventional WC-Cu composites(0.76,1.56 g).Meanwhile,the high-temperature compressive strength of carbonized W-Cu composite was higher than traditional W-Cu composite.