Multi-scale Numerical Simulation And Physical Experimental Study On Powder Metallurgy Preparation Of Pure Tungsten Metal And Tungsten-copper Alloy

The compaction and sintering stages of pure tungsten powders and tungsten-copper composite powders in powder metallurgy(PM)were systematically studied on the basis of microscopic particulate scale by using MPFEM method.The effects of particle size,po wder initial packing structure,compaction pressure,sintering temperature/sintering pressure,and Cu content on the relative densities of the green compacts and sintered parts of pure W metal and W-Cu alloy,internal stress/strain distributions therein,powder deformation and void filling behavior were systematically investigated.In addition,the densification dynamics and mechanisms were analyzed.Meanwhile,corresponding physical experiments were carried out to validate the effectiveness of the numerical model.The research results indicate that:(1)Pure W component with the relative density of 98%can be obtained after being sintered at a temperature of about 2000? when the particle size is 20 ?m and the compaction pressure is 500 MPa.(2)Tungsten particles with larger size are eligible to form much denser initial packings and green compacts.Meanwhile,more uniform stress distribution and much lower residual stress can be formed in the sintered components.But these enhancements become insignificant when the particle diameter is larger than 20 ?m.(3)During compaction of pure tungsten powders,the large pores formed in the initial packing are mainly filled by the rearrangement and tiny deformation of tungsten powders.However,large amount of remaining pores are filled by the growth of the sintered neck during sintering at the temperature of 300-1650 ?,which is induced by the softening effect of tungsten particles.(4)During the compaction and sintering processes of W/Cu composite powders,forces are mainly transmitted through W particles,which results in a high stress concentration;pores are mainly filled by Cu particles due to their large plastic deformation.With the increase of Cu content,the deformation of individual Cu particles is decreased.(5)For copper particles,the thermal strain will result in a decrease of stress during sintering;while for tungsten powders,the increase of plastic strain can cause the declining trend of stress during sintering.Compared with pressureless sintering,the sintering temperature reduce 400? when the pressure sintering method is used.