Research On The Preparation Of W-30cu Alloy By Hydrothermal Synthesis Method And Its Densification Process

W-Cu composite materials which combine both the characteristics of W and Cu, possess high density, high tensile strength, good thermal conductivity and electric properties, strong ability to absorb radiation, etc., therefore have been widely used in military, aeronautical, astronautical industry, electrical instrumentation and other fields. However, due to the mutual insolubility between W and Cu phases, in addition the high melting temperature of W(3410 ℃) compared to that of Cu(1083 ℃), W-Cu composite prepared by the conventional methods have drawbacks such as low densification, microstructure inhomogeneity which limit its further applications. It has been reported that the nano crystalline and the well-mixed state of component powders can enhance the sintering densification of powder products, in which the dominant sintering mechanism is known as to be the particle rearrangement. Thus, in recent investigations, the preparation of W-Cu alloy focused on the fabrication of ultrafine or nanosized W-Cu composite powders.In this paper, ultrafine-grained W-Cu composite materials with high performance were fabricated by hydrothermal synthesis method combined with spark plasma sintering and hot extrusion process on the basis of present conditions. And the electrical contact performances of hot-extruded compact were investigated. The main research results are showed as follows:The initial coprecipitation CuWO4·2H2O and Cu2WO4(OH)2 powder was prepared by hydrothermal method under conduction of pH=5.2. The hydro-thermal synthesis powder have slight soft reunion phenomenon exhibiting a regular spherical particle shape, fine dispersibility and the mean particle size was about 10 nm. After calcined at 550 ℃ for 2 h, a polycrystalline oxide mixture is obtained, and the main composition is CuWO4-x. The oxide powder exhibited polygonous morphology on the order of ~50 nm in size. After reducing the oxide products at 800 ℃ for 1 h, only pure W and Cu phases, and homogeneous distribution of both metals could be observed. The W-Cu nanocomposite powder size was growing up to 100-200 nm, had a microstructure composed of a W core surrounded by a Cu shell, not a mechanical mixture of nanosized W and Cu particles. And W-coated Cu structures in the size of 20-30 nm also exist in the reduced powder. Results show that the existence of Cu phase has played a catalytic role in reduction of tungsten oxide, and also the grain size was refined.Without compaction, the reduced W-Cu composite powders were immediately sintered by spark plasma sintering(SPS) process in 1050 ℃, and a ultrafine-grained W-Cu alloy with high distribution of both metals was obtained, especially the W particle has been great refined. Density, especially the hardness of the material has been greatly improved, but the conductivity of the material is generally low. Ultrafine-grained W-Cu composite materials with excellent performance were fabricated by vacuum-sintering and hot extrusion of W-30%Cu nanocomposite powders. The relative density of W-Cu alloy could simply reach 91.5% through vacuum-sintering at 1050 ℃, and reached 97.07% in relative density, 223 HB in hardness after hot extrusion process. During hot-extrusion, the molten copper phase form the capillary force to promote W particle rearrangement and filling porous, which make the organization more uniform, a typical Tungsten skeleton and copper network structure formed. The organization of the as-extruded W-Cu composites is fine dispersibility in W and Cu phases, and the grain size of W particle is only 1-3 μm. Subsequent heat treatment can eliminate the residual stress, further improve the organization and performance, thus the relative density and conductivity of composite reached 98.82% and 43.31 %IACS, respectively, good properties are obtained.The extruded W-Cu contact material has good electrical contact performances. The material transfer was from cathode to anode with voltage < 36 V, and from anode to cathode with voltage ≥ 36 V. Under the condition of stated current, the contact resistance value is stable that illustrates the arc ablation of W-Cu contact performance is perfect. The arc time and arc energy value increased and had a higher volatility with the increasing of circuit voltage. The contact erosion morphology analysis showed that the surface of the anode appear a large number of pits, holes and molten pools, while the cathode surface material mainly was the melting zone after solidification and molten drops.