Improving the mechanical properties and coefficient of thermal expansion of molybdenum-reinforced copper using powder metallurgy

This paper presents an experimental study of Cu-Mo alloys prepared by powder metallurgy (PM) method. Also, improving the dispersion and wettability of Mo in the Cu matrix was aimed. Mo particles were added by 0.24, 0.48, 0.73 and 0.97% volume fraction to Cu powder. The mixture was mechanically milled by planetary ball mill at a rotational speed of 140 rpm for 24 h under hydrogen atmosphere, with milling ball size of ∼25 times the size of the metal powders. Liquid acetone was utilized as a process control agent (PCA). Paraffin wax (0.5 wt%) was used to decrease the friction with die during the compaction process. The mixture of the blended powder was compacted at ambient temperature under three different pressures (400, 600 and 800 MPa) and then sintered in a vacuum furnace at 1000 °C for 1 h by a heating rate of 5 °C min⁻¹. The microstructure examination showed a homogeneous dispersion of Mo particles within the Cu matrix with no evidence of new phases formation during the sintering process. Also, the relative density of samples has been increased by increasing both of Mo content and the compaction pressure. The results revealed that the compaction pressure of 600 MPa was the most suitable pressure as it gave the highest densification. Cu—0.97% volume fraction Mo alloy samples exhibited finer Mo particles with a homogenous distribution in the Cu matrix and well bonding with the Cu particles. The microhardness was increased gradually by increasing Mo wt%, while the compressive strength was decreased by increasing the Mo contents. Both the electrical and thermal conductivities were decreased gradually by the addition of Mo. While the coefficient of thermal expansion (CTE) was decreased by Mo addition. (paper)