AMORPHOUS FORMATION PROCESSES OF AL-20 MOL-PERCENT CR ALLOYS BY MECHANICAL GRINDING OF EQUILIBRIUM INTERMETALLIC COMPOUNDS

The amorphization of Al-20 mol % Cr alloys were investigated when diff erent starting powders were mechanically ground using a vibration-mill . Mechanical grinding (MG) of two types of starting powders were exami ned: (1) single delta (Al-20 mol % Cr) phase powders and (2) a mixture of gamma (Al-15 mol % Cr) and epsilon (Al-30 mol % Cr) phases powders . Amorphous Al-Cr alloys could not be obtained by MG of single interme tallic compound (delta phase) as the starting powders. But in the case of MG using the mixture of intermetallic com pounds (gamma and epsilo n phases), some parts of the MG powders changed phase into an amorphou s phase with a Cr content of about 30 mol % at the initial stage of th e milling. On further milling, the formed amorphous phase reacted with residual crystalline gamma phase (Al-15 mol % Cr) to produce an amorp hous phase with a Cr content of 20 mol %. The former amorphous phase c rystallized into the delta and epsilon phases, and the latter crystall ized into an equilibrium delta phase by subsequent heat treatment.