Study On Rapid Sintering And Microstructure Of Ni-Al Phase Strengthened Tungsten Alloy

Tungsten alloys are used for armor-piercing projectile materials due to their high density,high strength,high hardness,no radiation pollution,and good machinability.However,the traditional 90～93 wt%W-Ni-Fe alloy is not sensitive to adiabatic shearing,and the warhead has reduced the penetration depth due to the“mushroom head”in the process of piercing.Therefore,in recent years,the development of new tungsten alloy materials with adiabatic shear sensitivity has become the focus of research.Ni3Al not only has the advantages of high specific strength and high temperature strength,but also has a positive temperature effect which easily causes adiabatic shear.Therefore,W-Ni3AI alloy is a potential armor material that can compete with depleted uranium kinetic penetrator.This paper focuses on the preparation of fine-grained W-Ni3AI alloy material and its microstructure and properties.The research contents are as follows:Firstly,the raw laterial powder pretreatment of W-Ni3Al alloy was completed by"two-step ball milling" and "electric discharge assisted ball milling" respectively,and a new fine-grained W-Ni3Al alloy with good comprehensive mechanical properties was prepared by rapid spark plasma sintering.It has been found that the use of "electric discharge assisted ball milling" can effectively refine the particle size of the powder and promote densification of fine-grained high-hardness alloys at low temperature.However,the powder after ball milling is more oxidized to form an Al2O3 phase and is not suitable for the formation of a flake binder phase structure at a certain scale,so the final bending strength and density are limited.A fine-grained W-Ni3Al alloy with a nearly full relative density(97.45%)and a grain size of 4.09 μm was prepared at 1400℃ by a two-step ball milling assisted spark plasma rapid sintering technique.Its bending strength and hardness are 958 MPa and 72.56 HRA,respectively.Secondly,on the basis of the "two-step ball milling" pretreatment,a W-Ni3AI-0.25G alloy with a relative density of 94.88%and good comprehensive properties was fabricated by a spark plasma sintering method at a temperature of 1350℃.And effect of graphene nanosheets on microstructure and properties of W-Ni3Al alloy was studied.The hardness and bending strength of the alloy were 75.37 HRA and 762 MPa,respectively.The grain size was 40.53%thinner than that of the unadded graphene sample,and the hardness of the alloy was increased by 3.6%.The results show that the addition of graphene nanosheets can effectively refine the alloy grains and improve the hardness of the alloy.However,excessive addition may result in difficulty in dispersion and agglomeration resulting in a large amount of pores and a decrease in the mechanical properties of the alloy.Finally,a series of carbon nanotube-reinforced fine-grained W-Ni3AI alloys with good comprehensive mechanical properties were prepared by spark plasma sintering at a temperature of 1350℃.The effects of adding different content of carbon nanotubes on the densification trend and microstructure of W-Ni3Al alloy were studied.As shown by the results,carbon nanotubes can hinder the sintering densification process and refine grains of W alloy to some extent.However,compared with graphene nanosheets,the fine-grain effect of carbon nanotubes on W-Ni3Al alloy is not significant.As the content of carbon nanotubes increases,the hardness of the alloy first increases and then decreases,and increases to 81.87 HRA when the amount is 0.75 wt%.The bending strength of the alloy gradually decreased from 642 MPa at 0.25 wt%to 322 MPa at 1 wt%.