Fabrication Of W-Cu Materials By Warm Compaction And Powder Injection Molding

Powder metallurgical tungsten-copper material is a kind of"pseudo-alloy"composed by tungsten with high strength and hardness, low thermal expansion and copper with high electrical conductivity and thermal conductivity, high plastic. Because of its excellent mechanical and physical properties, W-Cu materials are widely used in electric contacts, electronic packaging materials, heat sinks, high density alloys, leading wire frame in large scale compound integration.W-Cu alloys are usually fabricated by infiltration of desired tungsten skeletons with liquid copper or liquid-phase sintering of W-Cu powder compacts. However, full-dense W-Cu alloys with homogeneous microstructure and complex shapes are difficult to fabricate by these methods. Warm compaction and powder injection molding has excellent technique and economic advantages in fabricating high-dense iron based materials and parts with complex shapes, respectively. In this dissertation high-dense W-Cu materials and W-Cu alloys with complex shapes were tried to fabricate by warm compaction and powder injection molding, respectively. W-20wt%Cu powders were warm compacted with a new binder. Effects of compacting temperature, compacting pressure, particle size of the starting powder and binder content in the mixture on green density of the warm pressed W-Cu compacts were investigated, compared with those of cold compaction.Microstructures of the as-pressed and the as-sintered W-Cu parts formed by warm compaction and cold compaction were observed. Physical and mechanical properties of sintered W-Cu materials were also tested. The results show that warm compaction effectively increases the green density and green strength of W-Cu compacts. A maximum green density of 10.68g/cm3 and green strength of 22.06MPa were obtained for W-Cu compacts pressed at 170℃and 400MPa, which are 0.55 g/cm3 and 12.45MPa higher than that of cold compaction, respectively. The particle size of the starting Cu powder also has an obvious influence on green density of W-Cu compacts. Furthermore, effects of sintering temperature and forming method on the properties of sintered W-Cu alloys were investigated. Sintering densification mechanism, microstructures of the sintered samples were also analyzed. The warm pressed W-Cu compacts show higher sintered density than the cold pressed compacts, even the latter has higher sintering shrinkages. Sintered W-Cu materials from the warm pressed W-Cu compacts have improved microstructure and good physical and mechanical property. Properties of sintered W-Cu samples increase as the sintering temperature increases. Density of 95.58% of the theoretical was obtained for W-Cu compacts sintered at 1250℃for 2h. Vickers hardness and electrical conductivity are 249HV and 33.67%IACS respectively, higher than that of sintered cold pressed W-Cu parts.W-20wt%Cu compacts with ball shape were fabricated by powder injection molding using a binder based of high density polyethylene (HDPE). W-Cu alloys were obtained by sintering the PIM samples at temperature ranging 1050℃-1150℃in H2 atmosphere after solvent and thermal debinding. The process parameters during PIM, debinding time and temperatures of solvent debinding, heating rates during thermal debinding were optimized. The properties of the sintered balls were investigated and microstructures of the molded, debound and sintered W-Cu samples were observed by scanning electron microscope. The results show that optimal molding parameters for the feedstock are 180℃for injection temperature, 110bar for injection pressure, 30% of the stander injection speed for injection speed, and 50℃for mold temperature. In solvent debinding, debinding rate increases as the solvent temperature and time increase. Weight loss of binder reaches 62.26% in the solvent debinding at 55℃after 11h, the residual binders can be removed in the thermal debinding. During sintering, shrinkage, density and compressive strength of the sintered parts increase as sintering temperature increases. A relative density of 95.58% of the theoretical was achieved for W-Cu balls sintered at 1150℃for 2h in H2. The compressive strength and radial shrinkage are 58KN and 17.17%, respectively, for the W-Cu balls.