Research On Densification Of W-Cu Powders By Hot Extrusion And Plastic Deformation

W and Cu are liquid phase immiscible materials, also called as W-Cu composite. Generally, it is usually prepared by infiltration or liquid active sintering, but the density and properties (specific conductance and hardness) are usually unsatisfied. In order to obtain W-Cu materials in high-grade, the process such as vacuum hot-pressing or HIP is usually used to increase the relative density. Because of the low productive efficiency and high cost of vacuum hot-pressing and HIP, the application of W-Cu materials is limitted. This paper studied on the densification of W-Cu powders by hot extrusion with the Cu contents between 20~50wt.%, especially foucsed on the liquid phase extrusion process in order to substitute a new process for HIP.The recrystallization temperature of W (>1600℃) is much higher than the melting point of Cu (1083℃). Based on this feature, two different processes of powder densification by hot extrusion and plastic deformation are introduced in this paper. One is prepared by liquid sintering and hot hydrostatic extrusion, the other is prepared by canning hot extrusion between 1000~1150℃and particularly in the temperature of 1100℃. W-Cu materials is hard to be processed. So the plastic deformation of W-Cu materials prepared by liquid phase extrusion is also studied in order to diversify the product species of W-Cu as well as improving the properties.The uniformity of composite powders effects the properties of block materials severely. In this paper, the mixing and mechanical milling processes are studied. Comparing to machine mixing, the mechanical milling process with low speed can obtain composite powders of copper matrix attached by fine W particles. This structure guarantees the good uniformity of compact W-Cu materials. The liquid sintering and hot hydrostatic extrusion process is studied. After hot hydrostatic extrusion, the relative density and properties of W-Cu sintered billets are apparently improved. The relative density of W-40wt.%Cu is up to 98%, and the specific conductivity reaches 48%IACS with the hardness of about 140HV.This paper has payed major attention on the densification of W-Cu powders by canning hot extrusion. The basic regularitys on relative density and properties affected by extrusion temperature, milling time, extrusion ratio, can thickness, contents of Cu and heat treatment are experimentally studied. The relationship of extrusion temperature and the physical state of Cu is explored by the change of relative density, contents of Cu and distribution of Cu element on the edge of W-Cu materials. The result shows that, the liquid phase extrusion which means the compact with liquid Cu inside during extrusion can be achieved when the extrusion temperature at 1100℃. The appearance of liquid Cu is very helpful to improve the densification course and properties of W-Cu. When the extrusion temperature increase to 1150℃, the liquid Cu inside the compact exosmosed and aggregated to building a Cu rich zone. Though the relative density increased a lot, the specific conductivity decreased violently. After 1100℃liquid phase extrusion, the distribution of Cu inside W-40wt.%Cu material is uniform, the particle size of W is fine (2-3μm), the relative density is about 97%, the specific conductivity reaches 56%IACS, and the hardness is up to 215HV. In the liquid phase extrusion process, the relative density and specific conductivity decreased with increasing milling time, and increased with increasing extrusion ratio and contents of Cu. When the contents of Cu is between 30~50wt.%, the W-Cu materials with good properties are obtained by liquid phase extrusion. The liquid phase extrusion process has showed its advantages and obtained W-Cu materials with properties level almost reached the level of HIP process.Researched on the distribution of temperature, stress/strain and velocity fields of porous and steel can materials in powder canning extrusion process by numerical simulation. The influence on the highest temperature in the extrusion process and corresponding stress, maximum strain and the velocity of porous and steel can effected by extrusion temperature, extrusion velocity, extrusion ratio and can thickness was studied. The simulation and experimental results had reached a good agreement. Established the theoretical model of powder canning extrusion which was divided in two steps of multiple compress and steady-state flow. The densification equation and hydrostatic-pressure expression in the multiple compress step and the relationship between extrusion force and extrusion ratio, can size, relative density of porous in steady-state flow step were obtained.At last, the influence on relative density, mechanical property and structure property effected by different plastic deformation of dense materials prepared by liquid phase extrusion was studied. The increment of relative density of rolling is higher than upset, but is lower than second extrusion. The improvement of properties of W-Cu materials by upset and rolling is little, but remarkable by second extrusion. After second extrusion, the specific conductivity of W-40wt.%Cu materials reaches 60%IACS and the hardness is up to 230HV.Compared to the traditional sintering process, hot hydrostatic extrusion process can improve the relative density and properties of W-Cu. And the liquid phase extrusion process disposes the long time, high temperature vacuum sintering course and uses one-time forming technique without special atmosphere protection. It has the advantages of simple process, high productive efficiency, low cost and energy-saving/time-saving, and solves the problem of losing Cu when liquid sintering and precision controlling the percentage composition. It shows the huge priority on preparing W-Cu materials with Cu contents above 30wt.%. Either of the two process mentioned in this paper has obtained W-Cu materials with good properties. The relative density of liquid phase extrusion billet is a little lower than sintering-extrusion billet, but the specific conductivity and hardness are improved a lot. The liquid phase extrusion process is a predictable way to substitute for HIP process in preparing high-grade W-Cu materials.Recently, the research and patent reports about hot hydrostatic extrusion and powder canning extrusion of W-Cu materials have not been consulted yet, especially about the achievement of liquid phase extrusion process. At the same time, the study about plastic deformation of W-Cu is also rare. This paper creatively states a new liquid phase extrusion process to prepare immiscible alloy and obtains a good result. It shows the great importance on improving the development and application of W, Mo alloy in our country.