Effects of mechanical alloying on the characteristics of a nanocrystalline Ti–50at.%Al during hot pressing consolidation

Abstract

Two different powder metallurgy processes, i.e., reactive and non-reactive sintering, were investigated for the production of titanium aluminides. Ti–Al intermetallics have been successfully produced by mechanical alloying and hot pressing of powders with a nominal composition of Ti–50 at.%Al. A Ti(Al) solid solution was formed at the early stage of milling that transformed to an amorphous phase at longer milling times. On further milling, the amorphous structure transformed to a supersaturated hcp-Ti(Al) solid solution with trace amounts of TiAl after 80 h of milling, which was completely transformed to TiAl, Ti3Al, and TiAl3 intermetallic compounds after additional milling up to 100 h milling with particles of about 200 nm. Blended elemental powders and 100 h MA-ed powders were used for the reactive and non-reactive sintering processes, respectively. The results showed that the HP-ed pre-alloyed powder had better properties in terms of density, hardness, homogeneity of microstructure, yield stress, and ductility than that produced by reactive sintering. The major contribution to the yield stress of the sintered pre-alloyed powder comes from the nanometer-sized grains of intermetallics in accordance with the Hall–Petch relation.