| Mo-Cu composites exhibit excellent physical and mechanical properties, such as high thermal and electrical conductivity, low and alterable thermal expansion coefficient. They are widely used in some fields of electrical contact materials,thermal dissipation materials, electrical packaging materials. However, Mo-Cu alloy compacts can handly reach a high densification by conventional powder metallurgy methods. It requires us to improve the mutual compatibility and sintering density of Mo-Cu alloy. In this work, the chemical co-precipitation method was employed to prepare precursor powders of Mo-Cu. After subsequent calcination and reduction,superfine composite powders were finally obtained. Mo-40 Cu alloys with Cu contents up to 40 wt pct were obtained by vacuum sintering, spark plasma sintering and H2 atmosphere sintering, respectively. The precursor oxide powders, as well as the resulting Mo-Cu powders were characterized by XRD, FESEM and TEM. This article was focus on the effect of alloy’s microstructure and properties from the sintered compact prepared by three kinds of sintering process. Results were shown as follows:(1) Chemical co-precipitation and reduction method was innovatively used to synthetize Mo-Cu composite powders. Ultrafine Mo-40 Cu composite powders were fabricated with sodium molybdate dihydrate(Na2Mo O4·2H2O) and cupric chloride dehydrate(Cu Cl2·2H2O) as raw materials. Results show that a better craft is obtained as follows: The mixed solution was heated by water bath at 60 ℃, the precipitates were calcined at 350 ℃ in the furnace, and the precursors were reduced in H2 atmosphere at 750℃ to obtain superfine Mo-Cu composite powders. The morphology of Mo-Cu powders had exhibited an enhanced spherical morphology. In particular, the Mo-Cu powders exhibit a typical core-shell structure which was structurally comprised of a Cu core and a Mo shell. Superfine resultant particles with a particle size are about 80 nm. The size of a Cu core is about 50~60nm and the thickness of its shell is 30 nm approximately.(2) The effect of alloy’s microstructure and properties from the sintered compact prepared by three kinds of sintering process was studied. Results show that the Mo-40 Cu alloy, sintered at 1350 ℃ for 2 hours by vacuum sintering, exhibits good comprehensive properties. The relative density, bending strength and hardness of the Mo-40 Cu alloy reach 94.7%, 571 MPa and 118.9HV, respectively. The fracture of this material was mainly composed of microporous extension. After sintered at 1150 ℃for 10 min by SPS, the Mo-40 Cu alloy exhibits good comprehensive properties. The relative density, bending strength and hardness of the Mo-40 Cu alloy reach 95.6%,469.8MPa and 202.4HV, respectively. The fracture of this material was coexistent of microporous extension and ductile rupture. After sintered at 1300 ℃ for 2 hours by hydrogen atmosphere sintering, the Mo-40 Cu alloy obtained better relative density,bending strength, hardness, electrical resistivity, thermal conductivity, which is 98.3%,1005.4MPa, 166 HV, 6.5×10-8Ωm and 191.7W/m·K, respectively. The coefficient of thermal expansion is 10.8×10-6K-1at the temperature range from 500 ℃ ~700 ℃. The fractography shows that the grain size was about 4μm. The fracture mechanism is mainly composed of ductile fracture, molybdenum-copper binder interface separation and molybdenum particle cleavage were accompanied. After analyzing the relative density, mechanical properties and fractography, the results show that the Mo-40 Cu alloy fabricated by hydrogen atmosphere sintering is more excellent than other methods. |
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