Preparation And Properties Of High Density W-Cu Composites

High density alloys exhibit excellent physical and mechanical properties such as high strength and hardness, high thermal and electrical conductivity, low heat expansion coefficient, corrosion and oxidation resistance, good machining property and weld performance. W-Cu materials which consist of a mixture of almost pure W and Cu phases, as one category of high density alloys, have been widely used for heavy-duty electronic contacts and heat sink materials for high-power microelectronic devices because of the high electrical conductivity of Cu and the high arc erosion of W.In most of these applications, high density W-Cu components with homogeneous dispersion of tungsten and copper ingredients are often needed for high performance. The conventional methods for the fabrication of W-Cu alloys are infiltration of a porous tungsten skeleton with liquid copper, and the hot pressing of blends of tungsten and copper powders with subsequent liquid phase sintering. However, the infiltration technique is limited because it produces defects in the structure and the properties are sensitive to these defects. Furthermore, full densification of W-Cu alloy by this method is difficult due to the low solubility limit of W in liquid Cu and the high contact angle of liquid copper on tungsten. Traditionally, the addition of small amounts of Ni or Co can produce a high-density W-Cu composite by liquid phase sintering, but these additives significantly decrease thermal and electrical properties of copper matrix. Many researchers have tried to get W-Cu alloys of full density without sintering additives by increasing the fineness of W particles and homogeneity of the initial component particles in order to facilitate rearrangement of W particles in liquid Cu during liquid phase sintering.In this study, aqueous solution composed of ammonium metatungstate and copper nitrate were used as the starting material, by spray drying of aqueous salt solutions and a milling process followed by reduction of the oxide powder. This process yielded composite powders having ultrafine particles and homogeneous mixing state, reduction of a W-Cu-based oxide composite powder is investigated. The alloy has the transverse rupture strength (TRS) of 1109.6 MPa, with the Vickers hardness HV_0.1 2.40 GPa and Thermal conductivity (TC) of 174.5 W·m^-1·K^-1. Sintering behavior of the reduced powder is also investigated and various performance of sintered W-15Cu alloy is evaluated.In order to explore the effects of sintering method on the microstructure and performance of W-Cu alloys, the spark plasma sintering (SPS) process of W-Cu composite powders in lower temperature is investigated. The W-Cu alloy with higher performance than normal one was fabricated by SPS technology. Its TRS was 1259.1 MPa, Vickers hardness HV_0.1 was 3.78 GPa, and TC was 189.2 W·m^-1·K^-1. The results showed that the SPS technology had the great advantage of fast densification of alloys. The crystal growth inhibitors is introduced. Results showed that in optimum sinter point, TRS of W-Cu alloy doped with 0.3wt.% Y₂O₃ reached 1128.6MPa, and Vickers hardness HV_0.1 of W-Cu alloys doped with 0.5wt.% Y₂O₃ reached 2.78 GPa. As-fabricated alloys has better properties than the un-doped samples. Sintering behaviors of W-Cu composite powders prepared by different methods were compared. Composite powders prepared by spray drying-coreduction technology has higher singterability than that prepared by mechanical alloying.