Abstract
The microstructure of mechanically ground (MG) Ti-41 mol%Al alloy powder made by a vibratory ball mill, in the as-milled state as well as after heat treatment or vacuum hot pressing, was investigated. A new method for preparing TEM samples was employed which resolved the microstructure of the MG powder, whose particle sizes were more than 10μm in diameter. The alloy powder milled for 720ks was composed of fine grained α2 (Ti3Al), nanocrystals of Al supersaturated α-Ti and an amorphous phase. The a nanocrystals and the amorphpos phase presumably caused by milling of α2 and γ phases, respectively. The vacuum hot pressed compact showed ultra-fine equiaxed grain structure, with an average grain size of approximately 400nm. The similarity of the microstructure to that of mechanically alloyed (MA) compacts strongly suggests that the formation mechanism of the ultra-fine grain structure of the compacts is the same in both MG and MA processes.
