AMORPHIZATION BY MECHANICAL ALLOYING

The solid state amorphization methods of mechanical alloying (MA) of mixtures of elemental powders and mechanical milling (MM) of single component powder (intermetallic compound or element) are discussed. The mechanism for amorphization by MA is probably a variation of amorphization by interdiffusion of thin film diffusion couples with the added complication of the defects produced by plastic deformation. Mechanical milling of an equilibrium crystalline phase increases the crystal's free energy such that the crystalline-to-amorphous transition is favored. The defects introduced by plastic deformation give rise to such an increase in energy. Recent MM results are discussed which show that the stored energy of cold work introduced by ball milling can be large, and in pure Si and the Ni3Al intermetallic, the defects probably responsible for amorphization are the microcrystalline grain boundaries. © 1990.