Investigation on the distribution of Fe and Ni in reduced mo powders and its effects on the activated sintering of Mo compacts

Abstract

In this article, high densification Mo-1.0 wt.% Fe and Mo-1.0 wt.% Ni alloys were fabricated by a powder metallurgy technique. The distribution, chemical states and evolution of the doping elements within molybdenum powders were systematically investigated by serial analytical techniques, before further correlating to the microstructural development of solid-state sintered molybdenum compacts. The results indicated that after liquid-solid doping processing both Fe and Ni had been incorporated into the lattice sites of MoO3 and formed metal molybdates onto the surfaces of MoO3. The following hydrogen reduction produced nanometer thick Mo(Fe) solid solutions and Mo0.25Ni0.75 films at surfaces of Mo powders. Solid-state activated sintering was occurred in Fe/Ni doped Mo compacts under a sintering temperature of 1400 ºC. It was found that Fe remained at grain boundaries as Mo(Fe) solid solution in Mo-Fe alloy, which enabled to promote the diffusion of Mo atoms because of a lower vacancy formation energy. Grain boundary segregation of NiMo compound was identified in Mo-Ni alloy. This NiMo layer was transformed from the Mo0.25Ni0.75 coating in reduced Mo powders and served as a short-circuit diffusion paths for Mo atoms throughout sintering.