| Tungsten-copper (W-Cu) composites have been widely used to manufacture electric contact parts, welding electrodes, electricsparking and plasma electrodes, electric alloy, high-density alloy and some special use military materials due to its good resistance to arc erosion, welding resistance, high strength and hardness. W-Cu composite material is conventionally produced by infiltration of liquid copper into a porous tungsten piece sintered previously. However, the densification rate of composites prepared by infiltration method is slow, and the distribution of copper phase is not uniform. High temperature sintering makes tungsten particles grow up together to form coarse uneven organization and segregation occurs in the composition because of liquid copper over-spilled. Spark plasma sintering (SPS), as a novel electric current sintering method, can restrain the grain growth efficiently by reducing sintering temperature and holding time owing to the effect of cleaning and activating on particle from high pulsed electric current. So this method provides an efficient path for preparing high-density and fine grain tungsten-copper composites. For this reason, SPS technique was used to prepare W-20Cu-0.5Co composites in this paper. The main research work was as follows:High-energy ball milling was used to prepare W-20Cu-0.5Co powders, the shape and size of composite powders'particles were studied. Results showed that with the increase of the ball milling time, powders changed their initial shape polygon into layer flake, then gradually transformed into granular, and finally the grain size declined. After a long time ball milling, copper coated in the surface of tungsten particles. In the TEM photographs of 40 hours ball milling powders, grain had been refined to nano level.SPS technique was used to prepare W-20Cu-0.5Co composites from composite powders. The influences of sintering temperature, sintering pressure, sintering speed and holding time on the density, hardness, bending strength and conductivity were studied. It was easier to gain higher density, better bending strength and conductivity when using higher sintering temperature and pressure. However, if sintering temperature and pressure exceeded a certain limit, liquid copper would be squeezed out. Considering this, we usually chose 1060℃as the optimum sintering temperature,50MPa as sintering pressure. Too fast sintering speed was not conducive to the discharge of gas during sintering,30℃/min was selected as sintering speed to arrive at the target temperature after 900℃. Appropriate holding time was benefit to obtain dense tungsten-copper composites, so it was better to control the holding time in the range of 5 minutes to 10 minutes.SPS technique was used to prepare W-20Cu-0.5Co composites from different milling time composite powders. Influences of different milling time on performance of sintered specimens were studied. Research showed high-energy ball milling could increase the density of sintered specimens. However, too long ball milling time would introduce more impurities, which caused density a little decreased. With ball milling time increasing, hardness and bending strength of sintered specimens would be enhanced, while conductivity was gradually decreased. The main reason was that high-energy ball milling made the powder grain more refinement and tungsten particles uniformly dispersed in the copper matrix, which enhanced the mechanical properties of composite materials. At the same time, the grain refinement and a large quantity of lattice distortion strengthened electronic scattering, then deteriorated the conductivity of sintered materials. Therefore, mechanical properties and electrical conductivity was difficult to take into account. Composite powders milling for 30 hours were sintered by 50MPa to the target temperature of 1060℃and hold on for ten minutes, the relative density of sintered material reached 99.5%, hardness was 52HRC, bending strength could reach 725.6MPa and conductivity was 33.2IACS%, which showed good performance. It was similar to sinter different content copper of composite materials.Electric arc erosion properties of sintered materials had been studied. Burned by anodic arc erosion, ablation of anode material was greater than that of cathode. The anode surface formed a lot of pits and there were corresponding rough micro sags in the cathode surface. Many small metal balls which were molten metal splashed from anode could be seen in the surface of cathode. In the process of burning arc, we would not ignore phenomelon of tungsten powders sintered again. After electric arc erosion, different milling time powders sintered samples showed different erosion mophologies. The process of melting and coagulation was quite clear in the surface of samples sintered from mixed powders, a lot of melton pools and rich copper area could be seen. The pits became less and smaller in the surface of samples sintered from 40 hours ball milling powders, and none cracks could be seen. The surface turned smooth. Metal balls in the cathode surface splashed from anode became less and smaller. Increasing ball milling time did good to electric arc erosion property of tungsten-copper composite.
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