Preparation Of W-Cu Composites With Ultrafine Grains And Their Property Modified By Doping Rare Earth

W-Cu materials have been widely used in electric contacts, resistance welding electrodes, electronic packaging and heat sinks owing to their excellent properties such as high thermal and electrical conductivities, low thermal expansion coefficient and excellent mechanical property, etc. With the development of science and technology, higher performance requirements were raised gradually for W-Cu materials. Due to the mutual insolubility and large differences of melting point, density between W and Cu, it is difficult to obtain W-Cu composites with high relative density and high performance. This puts forward strict requirements to the powder metallurgy process for preparing W-Cu materials. In recent years, preparation of ultra-fine grained W-Cu composites and modifying the properties by doping rare earth become hot spots in the field of W-Cu materials and have achieved good results. In this dissertation, W-Cu powders were synthesized and W-Cu composites were prepared subsequently. The influences of rare earth oxides (Y2O3 and SDC) addition on the microstructure, density, room and elevated temperature mechanical physical properties of the W-Cu composites were also investigated, respectively:The main subject of this dissertation is to develop new routes for obtaining W-Cu composites with high performance.W-Cu precursor powders doped with 0-0.8 wt.% rare earth oxides (Y2O3 and SDC) were synthesized by EDTA-citrate method, in which ammonium meta-tungstate, copper nitrate, yttrium nitrate, cerous nitrate and samarium nitrate were used as the raw materials. W-Cu powders were obtained by calcining the precursor powders at 600 ℃ and coreduced at 700 to 800℃ in H2 atmosphere. Phase constitution and morphology of the W-Cu powders were measured by X-ray diffraction analysis (XRD) and scanning electron microscope (SEM). The results show that W-Cu powders with particle size from 100 to 200 nm were obtained. The addition of rare earth oxides suppresses the reduction and the growth of W-Cu powders. Although small amount of the dopant leads to the increase of reduction temperature, the particle size of W-Cu powders decreases and the powder homogeneity is improved.The resultant W-Cu powders doped with 0-0.8 wt.% rare earth oxides (Y2O3 and SDC) were compacted and sintered at 1150 to 1300℃ for 90 to 120 min in H2. Microstructure and performance of the sintered W-Cu samples were characterized. The results show that the W-20Cu powders have good sinterability, and the samples sintered at 1200℃ have relative density above 98%. Average grain size is less than 1 μm. Bending strength and Vickers hardness are about 940 MPa and 276 HV, respectively, and the electrical conductivity is above 41% IACS. At the temperature 25 to 600 ℃, tensile strength is from 383 to 125MPa, thermal conductivity is from 200 to 155 W·m-1·K-1 and thermal expansion coefficient is from 7.65 to 9.58×10-6K-1. The addition of rare earth oxides (Y2O3 and SDC) has no obvious influence on the physical properties of the W-Cu composites, but effectively improves the microstructure and mechanical properties. Maximum bending strength and Vickers hardness of Y2O3/W-Gu samples at room temperature reach 1040 MPa and 312 HV, respectively. The highest tensile strengths of Y2O3/W-Cu samples at room temperature and 600 ℃ are 421 MPa and 178 MPa, respectively. Maximum bending strength and Vickers hardness of SDC/W-Cu samples at room temperature is 1130 MPa and 318 HV, respectively, and the highest tensile strengths of SDC/W-Cu samples at room temperature and 600 ℃ reach to 580 MPa and 258 MPa, respectively.