Liquid phase sintering of mechanically alloyed Mo-Cu powders

In the Mo-Cu system, Mo has very low solubility in liquid Cu. To reach high densities after liquid phase sintering it is required the solution-reprecipitation step, which induces shape change. One technique that allows to form solids solutions out of equilibrium is the mechanical alloying. In the present work, the effect of the mechanical alloying of the elemental Mo and Cu (10, 20 and 30 vol%) powders and the sintering atmosphere (Ar vs Ar + 10 vol% H-2) on the densification, microstructure and hardness of sintered samples in liquid phase at 1150 degrees C for 1 h, was studied. It is hypothesized that the sintering can be facilitated by the generation of a solid solution of Mo in Cu out of equilibrium which, allows the Mo to enter solution in the Cu liquid and re-precipitate on the solid Mo particles during the process. The results show that mechanically alloyed Mo-Cu and sintered powders in the reducing atmosphere of Ar + 10 vol% H-2, have the highest densities and densification of all studied alloys. This is explained by the formation of solid solution of Mo in Cu during the mechanical alloying, evidenced by the EDS analysis. It is suggested that these milled and sintered powders reach the highest hardness due to their microstructural refinement, high density of Mo dislocations and low porosity.