Study On The Manufacturing Process Properties Of Tungsten Alloy Additives By Selective Electron Beam Melting

Tungsten alloy has the characteristics of high melting point,high density,high high-temperature strength,low coefficient of linear expansion,good corrosion resistance and oxidation resistance,and is an ideal material for hot work molds.At present,tungsten alloys are mainly prepared using powder metallurgy methods,but due to the high melting point and room temperature inherent brittleness of tungsten,it is difficult to prepare some complex structures such as curved surfaces,flow channels,or porous molds.Additive manufacturing technology using high-energy beams such as lasers and electron beams as heat sources has unique advantages in the forming and manufacturing of complex structural components.Selective electron beam melting（SEBM）technology uses electron beams as the heat source,which has higher energy density and utilization efficiency than lasers.The formed parts have less deformation and are formed in a vacuum environment,providing an effective way for the preparation of complex structural parts of refractory metals such as tungsten alloys.This article uses SEBM technology to prepare 90W-7Ni-3Fe（wt.%）alloy.Through finite element simulation method,the influence of SEBM process parameters and scanning path on the instantaneous temperature field of the molten pool during SEBM preparation process is studied,and preliminary optimization of process parameters and scanning path is achieved.Through experimental research,the influence of process parameters on the microstructure,density,mechanical properties,and wear performance of tungsten alloy formed parts is analyzed,Explore the changes in microstructure,phase structure,and density of tungsten alloys under different heat treatment processes,as well as the impact mechanism on mechanical and wear properties.In the finite element simulation of SEBM process,when the scanning speed is1.6m/s,the scanning power is 720W,the overlap rate is 50%,and the spot diameter is0.2mm,the tungsten alloy has sufficient cooling time and melt pool temperature to melt the bonding phase,and the tungsten particles are coated,which can effectively rearrange the tungsten particles.The simulated forming temperature under this parameter is more suitable,reducing the range of process experiments and providing reference for subsequent experimental work.Based on the finite element simulation results of tungsten alloy SEBM process,adjust the SEBM process parameters（electron beam current and scanning speed）to explore the microstructure,density,hardness,and friction and wear properties of tungsten alloy under different process parameters.The results show that when the energy density of the electron beam is insufficient,the temperature of the molten pool is low,the cooling rate is fast,and the fluidity of the liquid bonding phase is not sufficient to completely fill the gaps between tungsten particles,resulting in a large number of pores inside the formed part;The energy density of the electron beam is too high,the temperature of the molten pool far exceeds the boiling point of the bonding phase,and a large amount of volatilization occurs in the bonding phase.The residual amount of the bonding phase is not enough to fill the pores between tungsten particles,and the pores gradually increase again.The experimental results show that when the electron beam current is 14m A～16m A and the scanning speed is in the range of1.2m/s～1.6m/s,there are fewer pores,the powder fusion is good,and the highest density reaches 88.57%.During SEBM process of tungsten alloy,when the energy density of the electron beam is insufficient,the temperature of the melt pool is low,the cooling rate is fast,and the fluidity of the liquid bonding phase is not sufficient to completely fill the gaps between tungsten particles,resulting in a large number of pores inside the formed part;The energy density of the electron beam is too high,the temperature of the molten pool far exceeds the boiling point of the bonding phase,and a large amount of volatilization occurs in the bonding phase.The residual amount of the bonding phase is not enough to fill the pores between tungsten particles,and the pores gradually increase again.The experimental results show that the electron beam current ranges from 14m A to 16m A,and the scanning speed ranges from 1.2m/s to 1.6m/s with fewer pores.The powder has good fusion,and the highest density can reach 88.57%.In order to further improve the microstructure and properties of SEBM formed tungsten alloy,the formed parts were subjected to heat treatment at 1150℃for 4 hours and 1150℃for 2 hours,respectively.Through comparative analysis,it can be concluded that the microstructure and properties of tungsten alloy formed after heating at 1150℃and holding for 2 hours of heat treatment are excellent.The distribution of bonding phase and tungsten particles is relatively uniform,and the segregation of tungsten dendrites is effectively improved,with the actual density reaching up to16.05g/cm³ and the density reaching 93.86%;The tensile strength reaches 720.96MPa,and the fracture morphology is mainly characterized by W particle transgranular fracture;Effectively improving friction and wear performance,reducing the friction coefficient from 0.79 before heat treatment to 0.39,and reducing the wear volume from2.13×10^-2mm³ to 1.08×10^-2mm³.