| Tungsten-copper alloy combines the performance characteristics of tungsten and copper,which shows good arc erosion resistance and welding resistance,higher hardness,high temperature strength,high electrical and thermal conductivity,small expansion coefficient and good plasticity.Since tungsten and copper are not soluble with each other,the actual alloy formed is a structural pseudoalloy.The infiltration method is a relatively common technique for preparing high-performance tungsten/copper alloys.The tungsten-copper alloys obtained have high relative density and excellent performance.The research on the preparation of tungsten-copper alloys by infiltration method is mainly based on physical experiments,and it is difficult to explain the dynamic characteristics and densification mechanism in the material preparation process from the microscopic scale.In view of the shortcomings in current researches,this paper takes 9 tungsten particles as the research object and uses different finite element models to simulate the impregnation of molten copper in the tungsten skeleton during the infiltration process of preparing tungsten-copper alloy from the particle scale.The filling rules of copper infiltration in the prepared tungsten framework were systematically studied,and the mechanism of pore defect generation was analyzed.During the preparation of tungsten skeleton,the effects of porosity and tungsten particle size on the infiltration process were studied.In the molten copper infiltration stage,the influence of infiltration atmosphere(hydrogen and air)and wettability on the infiltration process was analyzed.The main results obtained in the paper are as follows.(1)During the pore infiltration of copper in the tungsten skeleton,there is a fast filling period and a steady filling period when filling each layer of the tungsten skeleton.The upper tungsten skeleton is filled faster than the lower layer,and the copper velocity is more than 1 m/s while only 0.1 m/s during the steady filling period can be reached.In the air infiltration atmosphere,porosity defects will be generated at the center of the tungsten skeleton during the process of impregnation.This is mainly because copper has different flow speeds at different positions,the gas cannot be discharged in time,which will result in the stress concentration near the void.(2)The influence of the porosity and particle size of the tungsten skeleton on the molten copper impregnation process is as follows:the smaller the tungsten skeleton porosity,the more likely it is to produce large pore defects;but at the same time,the pores are more likely to escape to the nearest liquid.And with the decrease of the porosity,the filling rate of the molten copper into tungsten skeleton near the boundary layer of the unit system will decrease.The smaller the size of tungsten particles,the larger the stress at the pore structure.The internal stress of the pores generated by the infiltration of the tungsten skeleton with a particle size of 2 μm reaches 70,000 Pa,and the pores are more easily discharged from the liquid phase.(3)The influence of infiltration atmosphere and interfacial wettability on the process of infiltrating tungsten framework of molten copper is as follows:Compared with the infiltration in the air,the copper infiltration into tungsten framework in hydrogen atmosphere is less likely to produce porosity defects.And in the rapid filling stage,the filling of copper in the pores of tungsten skeleton is faster.The wettability of the interface between the molten copper and the tungsten skeleton also affects the process of infiltration.The smaller the contact angle,the greater the pressure on the flow front during the rapid filling of the tungsten skeleton.At a contact angle of 5°,the negative pressure at the copper flow frontier reaches 10000 Pa,and the corresponding negative pressure is about 5000 Pa when the contact angle is 45°.At the same time,the greater the copper flow velocity,the closer the boundary layer,and the more obvious this difference. |
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