Mechanical alloying by ball milling of Ti and Mg elemental powders: Operation condition considerations

It was possible to identify the combined effects of the magnesium powder particle size, the milling speed, milling time and the process control agent (PCA) on the transformation steps, the microstructure evolution, the effectiveness of solid-state solubilisation of titanium and magnesium, and the yield of the ball milling process in a Simoloyer CM01-2lm. Starting with coarse ductile magnesium powder particles (300–600 μm) that are 10 times larger than the titanium particles led to different process steps than those observed when both elemental particles were fine (<45 μm) in high-energy ball milling. The interior of the milled particles remained 100% magnesium. However, formation of a metastable Ti50Mg50 solid solution was achieved by high-energy ball milling of fine powders of elemental titanium and magnesium processed for more than 24 h. The yield of the ball milling dropped drastically when the milling time became longer than 24 h. Coarse magnesium chips led systematically to lower yield. Further milling of the powder adhering on the wall of the jar led to a high densification of the heterogeneous cold welded layer but not to any improved mechanical alloying. Mechanical alloying only took place inside the jar where fine elemental powder particles are efficiently impacted between the moving milling balls.