W-Cu composites combine the high strength,high hardness,low expansion coefficient of tungsten and high thermal and electrical conductivity of copper.Due to its comprehensive performance,it is widely used in electronic devices,military industry,aerospace and other fields.The traditional powder metallurgy method and infiltration process are difficult to obtain W-Cu materials with complex shape and uniform microstructure,which can not meet the requirements of modern technology to develop high-performance complex parts.Metal injection moulding(MIM)technology has the advantage of technology and cost in manufacturing small and complex parts compared with conventional processes.Although the incompatibility of W and Cu and the difficulty of densification limit the production of W-Cu composites by injection moulding to a certain extent,W-Cu products with satisfactory size and properties can be obtained by choosing appropriate injection moulding process parameters and binder composition.W-20wt%Cu composites were prepared by injection moulding with paraffinbased binder system.The injection moulding process of W-Cu composites was studied from two aspects of process parameters optimization and binder optimization.The mechanism of the influence of injection moulding processes on the size and properties of injection samples was analyzed.The optimum process parameters of injection moulding were explored.In the original wax-based binder,the W-20wt%Cu composites were prepared by injection moulding.The optimum design was carried out on the basis of composition.This paper adopts 66PW-15EVA-15HDPE-4SA binder system and W-Cu powder mixed powder loading for 58vt% feedstocks.After injection moulding,the binder in the green injection billet was removed by solvent degreasing and thermal degreasing.Finally,W-20 Cu composite was obtained by sintering.The effects of injection parameters on the size and mechanical properties of injection samples were studied from five aspects: feed preparation,injection molding,solvent degreasing,thermal degreasing and sintering.The results show that the injection process parameters have an important influence on the defect control,the bending strength and the conformity of the green body.W-Cu injection green part with high strength and no defects can be obtained at the injection temperature of 165℃,injection pressure of 110 bar and injection speed of 40%.In the process of solvent degreasing,the solvent degreasing rate increases with the increase of temperature,time and powder loading.In addition,the mechanism of solvent degreasing was analyzed,and the kinetic constants of solvent degreasing at different temperatures were calculated,which provides a theoretical reference for the process design of solvent degreasing in production.The weight loss of binder during thermal degreasing was analyzed by TG-DSC curves of binder and feeding material.The thermal degreasing process was formulated to obtain defect-free and strength-free green slabs.The mechanical properties of the green slabs increased with the increase of the maximum temperature of thermal degreasing.The bending strength of the green slabs could reach 83.87 MPa at 950℃.In the final sintering process,W-Cu sintered samples with density increases with the rising of sintering temperature,sintering 2 hours at 1300℃ in hydrogen atmosphere,density of sintered W-Cu samples reached as high as 94.74%.On the basis of preparing W-Cu composite material with the original paraffin base binder,in order to improve the performance of the wax matrix in the binder,this paper prepared W-20 Cu composite material under the original injection process parameters by adding a certain amount of microcrystalline wax into the paraffin to prepare the wax matrix.Studies have shown that the injection temperature range of W-Cu injection feedstock can be increased by adding different content of microcrystalline wax,and the green injection blank with better strength can be obtained.W-Cu injection green billet containing microcrystalline wax still has higher bending strength after solvent degreasing and thermal degreasing.It may be because when microcrystalline wax is used as paraffin matrix,it can be mixed more evenly with binder,so that a more uniform pore channel can be formed in the degreased green billet after degreasing,which is conducive to more uniform contact between powder particles.When the microcrystalline wax with a mass fraction of 20% was added into the binder,the solvent degreasing rate of the raw blank injected by W-Cu was the fastest,and the density of the sintered sample was the highest at 95.02%,with good mechanical properties and conformability. |