| Low-copper Mo-Cu alloys are extensively used owing to its excellent characteristics such as high thermal conductivity, low coefficient of thermal expansion(CTE), low weight, nonmagnetic and well high-temperature behavior, these have been widely employed in applications such as electronic packaging, contact alloy and heat sink materials. Mo-18Cu alloys with Cu contents up to 18 wt pct prepared by mechanical alloying (MA) of raw powders were denstified by H2 atmosphere sintering, activated sintering and spark plasma sintering, respectively. The effect of powder milling process and sintering process on microstructure and properties of Mo-18Cu alloy was systematically investigated. The Mo-18Cu alloy with better comprehensive properties was obtained. Results were shown as follows:1.The average particle size of composite powder reached 1.25μm after milling 60 hours, which was homogeneous and fine. Most of the Cu particle was leaded to the large grain boundary which was afforded by the Mo particle, and then the sub-mutual solid solution was formed. The composite powder sintering activity and characteristics can be improved.2.After sintered at 1350oC for 2 hours, the Mo-18Cu alloy obtained better relative density, bending strength, hardness, electrical resistivity, thermal conductivity, which was 98%, 581MPa, 64HRA, 6.8×10-8Ωm and 160 W·m-1·K-1, respectively. The coefficient of thermal expansion was 7.2×10-6k-1 at the testing temperature range from 400oC～600oC. The fractography showed the microstructure of Mo-18Cu was homogeneous and compact network, and the grain size was about 2.5μm. The fracture mechanism of this material was the coexistence of brittle and ductile rupture.3.The activating element of Ni, Co and Fe can improve the relative density and mechanical properties of Mo-18Cu alloy and decrease the sintering temperature, while the physical properties such as electrical conduction and thermal conductivity became worse. Three kinds of activating element with weight ratio of 1.0wt%, 1.5wt%, 2.0wt% and 2.5wt% were investigated in this experiment. The results showed that the Mo-18Cu alloy with 1.5wt% Ni content had better comprehensive properties, which the relative density, bending strength, hardness, resistivity and thermal conductivity reached 99.5%, 1058MPa,78HRA, 1.28×10-7Ωm and 145 W·m-1·K-1, respectively. The coefficient of thermal expansion of Mo-18Cu alloy with Ni1.5wt% reached 5.6×10-6K-1 at 100oC, and increased with the temperature improving, which was nearly the same to that of the Al2O3 ceramic materials. The sintering temperature decreased 100 oC by activated sintering compared to H2 atmosphere sintering. The fractography of Mo-18Cu alloy with 1.5wt% Ni content was more homogeneous and compact than that was made by H2 atmosphere sintering, and the grain size was about 2.0μm. The activating element of Co and Fe had worse activated efficient than Ni, and the Mo-18Cu alloy with Co or Fe content had worse comprehensive properties.4.SPS technique has also been utilized for preparing high dense Mo-18Cu alloy at lower temperature in short time compared to H2 atmosphere sintering. After sintered at 1200oC for 10mins with the axial pressure of 30MPa, the Mo-18Cu alloy obtained better relative density, bending strength, hardness, electrical resistivity, thermal conductivity , which was 99.5%, 80HRA, 965MPa, 5.5×10-8Ωm and 175 W·m-1·K-1, respectively. The coefficient of thermal expansion was 7.38×10-6K-1 at the temperature range from 400oC～600oC , which was closed to the theoretical value of 7.43×10-6K-1. The fractography of Mo-18Cu alloy was homogeneous and fine, and the grain size was about 1.5μm. After analyzing the relative density, mechanical properties, physical properties and fractography, the result showed that the Mo-18Cu alloy fabricated by SPS was more excellent than other methods. |
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