Amorphization reactions during mechanical alloying/milling of metallic powders

Solid-state amorphization reactions resulting from the severe mechanical deformation obtained by high-energy ball milling are reviewed. Two classes of such reactions are discussed: 1. “mechanical alloying” where material transfer occurs between elemental powders or alloys, and 2. “mechanical milling” where an equilibrium crystalline intermediate phase is transformed to the amorphous structure by milling. The thermodynamic and kinetic criteria for the crystalline-to-amorphous transition are outlined. Recent experimental results from the author's laboratory on the amorphization of intermediate phases by milling are presented. The implications of these results for mechanisms of the crystalline-to-amorphous transformation are discussed.