Research On Selective Electron Beam Melting Of Pure Tungsten

Tungsten has an important application in national defense,medical treatment,chemical industry and other fields,because of its high melting point,high hardness,high elastic modulus,high thermal impact resistance,low expansion coefficient,good high temperature strength and other characteristics.However,due to the high melting point and brittleness of tungsten at room temperature,it is a great challenge to manufacture complex components by traditional manufacturing methods.Additive manufacturing technology is a revolutionary near-net forming technology developed in recent years.Among them,Selective electron beam melting(SEBM)with large power and high energy utilization rate,low residual stress,the outstanding advantages of high vacuum without pollution,especially suitable for tungsten and other rare and refractory metal rapid manufacturing of complicated components.In this paper,the irregular tungsten powder was used as raw material,and the SEBM technology was used to carry out the exploration research on the forming process of pure tungsten sample.The influence of process parameters such as melting current,scanning speed and line spacing on the forming quality of pure tungsten samples was studied.The microstructure,compressive strength and microhardness of SEBM shaped tungsten samples were characterized by SEM,OM,EBSD and universal material testing machine.The main conclusions were as follows:(1)Unlike titanium alloy and nickel alloy formed by SEBM technology,pure tungsten formed by SEBM does not need preheating,and the snaking scanning method can effectively prevent the generation of macroscopic cracks in the process of SEBM forming under the condition that the powder bed is not preheated.(2)Through the optimization of the process parameters,a nearly pure tungsten sample can be obtained.The relative density of the pure tungsten sample prepared by SEBM technology is up to 99.5%;(3)The pure tungsten formed by SEBM technology consists of coarse columnar crystals parallel to the growth direction,and the grain orientation is<100>//Z and<111>//Z,and the grain length is about 200 μm,and the width is 50-150 μm.(4)The hardness of pure tungsten formed by SEBM technology can reach above 500HV,which is higher than that of tungsten prepared by traditional technology,and the compressive strength shows obvious anisotropy due to the microstructure characteristics of columnar crystal.