Study On Solid State Alloying Of W-Ta/Re Powder And Its Co-Sintering Characteristics With Ni-Fe System

Tungsten is a refractory metal with high density,high melting point,high hardness and good chemical stability.It is widely used in military equipment,aerospace and industrial production.However,pure tungsten has obvious room temperature brittleness due to low dislocation mobility at room temperature and large slip force.The failure of traditional W-Ni-Fe alloys is also dominated by the transgranular cleavage fracture of W particles.Therefore,improving the intrinsic brittleness of W particles is of great significance for improving the strength and toughness of tungsten alloys.Ta and Re elements have good lattice matching with W,and can reduce the resistance of dislocation motion after solid solution with W,thereby improving the intrinsic properties of W.Based on this,from the perspective of solid solution modification,W-Ta/Re alloy powder was prepared by solid-state alloying method.90（W-Ta）-7Ni-3Fe and 90（W-Re）-7Ni-3Fe alloys were prepared by co-sintering with Ni-Fe System with W-Ta/Re solid solution particles instead of W particles as sintering core.The microstructure and phase evolution of solid alloyed powder were systematically studied.The effects of pre alloyed Ta and Re on the sintering structure,element diffusion,phase transformation and mechanical properties of tungsten alloy were investigated.The main results are as follows:（1）The solid-state alloying process of W-Ta and W-Re powders goes through several stages:powder calendering deformation,crushing refinement and cold welding fracture balance.W-20wt.%Ta/Re solid solution powder with low impurity and uniform element distribution can be prepared by using cemented carbide ball milling tank and ball milling beads at 300 rpm,anhydrous ethanol as ball milling medium,ball material ratio of 10:1 and ball milling for 60 h.（2）90（W-Ta）-Ni-Fe alloy was prepared with pre alloyed W-Ta powder as skeleton.The synergistic strengthening mechanism of solid solution of tungsten particles and nano precipitation of matrix phase was revealed.90（W-Ta）-Ni-Fe alloy sintered at 1450℃for 1 h can achieve a density of more than 98%.The solid solution of Ta strengthens W particles,and the precipitated acicular phase strengthens the bonding phase,which increases the overall hardness of the alloy.During the sintering heating process,the solid solution Ta precipitates from W-Ta particles,and eutectic reaction occurs with Ni,which reduces the liquid phase formation temperature.During the cooling process,peritectic reaction occurs in the bonding phase,and nano acicular Ni₃Ta phase is precipitated,which improves the microstructure uniformity and the density of the alloy.Compared with the traditional direct addition,pre alloying changes the interface failure of the alloy into the ductile tearing of W particle transgranular cleavage and matrix phase,which increases the tensile strength of the alloy.（3）The mechanism of element diffusion and grain refinement in the co-sintering process of W-Re alloy powder and Ni-Fe system was revealed,and the high-strength 90（W-Re）-Ni-Fe alloy was successfully prepared.The optimum sintering process of the alloy is holding at 1480℃for 1.5 h.Re dissolved by pre-alloying is mainly retained in W particles after sintering.A small amount of Re entering the matrix phase does not react with Ni Fe,but forms a uniform phaseγ-（Ni,Fe,Re）solid solution.Due to the solid solution of Re in the matrix phase,the dissolution and precipitation process of W particles is inhibited,and the average grain size of W particles is reduced from 33.78μm to 12.67μm.The tensile strength and hardness of 90（W-Re）-Ni-Fe alloy were significantly improved due to fine grain strengthening and solid solution strengthening,and reached the highest strength of 1.05 GPa at 5 wt.%.However,the failure mode of the alloy changed from transgranular fracture to interface failure between W particles and matrix phase,resulting in the decrease of toughness.