Effect of powder size and geometry on consolidation of Mo30%W alloy by spark plasma sintering

Abstract

Molybdenum alloys are important structural components for a variety of high temperature applications in the aerospace and nuclear industries. Spark plasma sintering has been successful in producing highly dense refractory metals with desirable microstructural characteristics, where the final microstructure and sintering mechanisms depend heavily on the starting powder size and morphology. To understand how powder size and morphology affect consolidation of a molybdenum 30 wt% tungsten alloy (Mo30W), three different powder feedstocks were sintered and the solid compacts characterized. These powders were prepared utilizing chemical reduction, ball-milling, and gas atomization processes. Additionally, to determine the effect of particle size on sintering, two different size distributions of the gas atomized material were also tested. In-situ sintering dilatometry data was analyzed to determine the apparent activation energy for the initial stage sintering of each powder. Powder geometry was found to have the greatest impact on the sintering of Mo30W powders, with the rougher, more angular powders densifying at lower temperatures compared with the smoother spherical powders densifying at higher temperatures. Powder size contributed much less to the densification of the powders using SPS. From these experiments, optimum sintering temperatures can be determined, with 1600 °C being sufficiently high to fully densify the chemical reduction and ball-milled materials and a maximum hold temperature of >1800 °C being required for the spherical atomized powders.