Preparation Of Novel W-Cu Composites And Their Microstructure And Performance

Tungsten-copper composite is a pseudo-alloy formed by the combination of tungsten and copper in a certain proportion.It combines the high strength,hardness,thermal conductivity and superior conductivity of tungsten and copper.It is utilized to prepare electrical contact materials,high temperature resistant materials,electronic packaging and heat sink components.Because tungsten and copper are insoluble,their wettability is poor,and they have a high melting point difference,it is difficult to obtain fully dense tungsten-copper composites by the traditional powder metallurgy method.Therefore,increasing sintering density,reducing sintering temperature and improving comprehensive properties are the hot topics in W-Cu composites.In this dissertation,three layers of W-Cu gradient materials were prepared by powder metallurgy,and their deformation and failure under thermal shock and laser heat shock were studied.In addition,W-Cu composites with high performance can be obtained by adding RGO and refining the original powder grains.The main contents of this paper are as followings:(1)W-10Cu(wt.%)composite powder was prepared by electroless plating method;W-20Cu and W-30Cu composite powders were obtained by adding Cu powder to W-10Cu powder.Gradient W-Cu alloy were prepared by laminating pressing three kinds of composite powder and sintering on H₂.The experimental results show that the three layered W-Cu gradient materials with a density of 96.9%can be obtained by sintering the layered green compacts at 1350?for 120min,The thermal conductivity of the sintered samples reach 217W/(m·K).The three layered gradient W-Cu samples were heated and cooled internately 30 times,60 times and 90 times in 1000?,respectively.It was found that thermal shock would make the copper in W-Cu gradient materials enriched at the interface between the 10Cu layer,the 20Culayer and the 30Cu layer.The interface deformation between the 30Cu layer and the 20Cu layer was obvious,but there is no crack;Cracks extend from the edge to the center of the interface between the 10Cu and the 20Cu layers.Taking the low copper layer(W-10Cu)as the thermal impact interface to observe the damage of the gradient materials after thermal impact under different laser power density,the results show that the laser thermal shock will form a conical mass loss area in the W-10Cu layer,and its depth increases with the increase of laser power density,and the depth of the ablation area is 1157?m when the heat flux of the laser beam is 1.35 MW/m²·s^1/2.(2)Cu-RGO composite powders and W-Cu composite powders were prepared by electroless plating method,and RGO enhanced W-20Cu composites were prepared by Spark Plasma Sintering.The morphology and phase composition of composite powders were investigated,and the density,microstructure and properties of the blocks after sintering were tested.The experimental results demonstrate that the mechanical properties and thermal conductivity of the W-Cu composites can be improved by adding RGO to W-Cu composites.And thermal conductivity,flexural strength and microhardness of the W-20Cu-0.5RGO samples are 237 W/(m.K),960MPa,248.5HV,respectively.(3)Using ammonium nitrate,ammonium tungstate,copper nitrate and glycine as raw materials,ultrafine W-30Cu composite powder was prepared by the solution combustion synthesis-hydrogen reduction method.The process of solution combustion was explored,and the reaction mechanism of solution combustion synthesis was revealed by means of XRD,TG-DSC-MS and SEM,which provided a basis for better control of the reaction.Experiments results show that the precursor powders prepared by the synthesis of solution combustion can be reduced to W-30Cu composite powders with grain size less than 20nm at 700?for 120min in H₂.W-30Cu composites with a density of 98.6%can be prepared by using the powders after sintering at 1200?for 120min,and their microhardness and thermal conductivity are 245.6HV and 223.55W/(m·K),respectively.