We have found that a cyclic crystalline–amorphous phase transformation can occur inCo75Ti25alloy powder when subjected to ball milling. The results have shown that a single amorphous phase ofCo75Ti25is obtained after 11 ks of mechanical alloying (MA) time. This amorphous phase transforms into a new metastable phase ofbcc-Co3Tiupon milling for 86 ks. Thebcc-Co3Tiis thermally stable and does not transform to any other phase(s) upon heating up to 1300 K. It however returns to the same amorphous phase ofCo75Ti25upon milling for 360 ks. Further milling leads to the formation of crystalline and/or amorphous phases depending on the MA time. ©1997 American Institute of Physics.