Densification and property improvement of Mo-Cu immiscible alloys processed by repressing and re-sintering

Abstract

Mo-Cu immiscible alloys, due to their good electrical and thermal conductivities as well as excellent mechanical properties, exhibit great application potential as electrical-contact and thermal-management materials in power transportation, domestic appliance and electronic information fields. However, the immiscibility and low wetting ability of Mo and Cu tend to cause that the low relative density and poor physical-mechanical properties of Mo-Cu alloys prepared by conventional powder metallurgy technologies. In this work, repressing and re-sintering technologies together with powder pretreatment are employed to densify Mo-25Cu (wt%) immiscible alloys processed by a liquid sintering with H₂ protection and thus improve their physical-mechanical properties. The results indicate that microstructures of all alloys mainly consist of Mo phase domains surrounded by mesh Cu phases. With repressing and re-sintering proceeding, relative densities and physical-mechanical properties of the alloys processed by whether the mixed powder or the milled powder both gradually increase. This mainly results from two aspects of reasons: i) the capillary filling effect of Cu melt during the sintering and ii) the collective motion of two phases dominated by the plastic deformation of meshy Cu phase during the isostatic loading. More importantly, it is found that all properties of the consolidated alloys using the milled powder are better, which could be attributed to the relatively even microstructure because of the more homogeneous phase distribution in the milled powder. This study can promote the advance of investigations on processing, microstructure and properties of high-performance immiscible alloys manufactured by net shape forming.