FORMATION PROCESS OF THE AMORPHOUS MGNI BY MECHANICAL ALLOYING

To clarify the formation process of amorphous MgNi (a-MgNi) by mechani cal alloying (MA), we have investigated the time evolution of structur al changes of the alloy, Mg-50 at.%Ni, synthesized from Mg2Ni and Ni p owders under various MA-times. The amorphous-like phase in the powder particle of the alloy increases with increasing MA-time, and the almos t single a-MgNi phase is formed after 288 ks of MA-time. At an earlier stage in MA, the crystals of Mg2Ni are nanostructured, and the nanost ructured Mg2Ni (n-Mg2Ni) and Ni are kneaded with each other in the pow der particles. With increasing MA-time, the n-Mg2Ni region containing Ni kneaded has increased and transformed to the amorphous-like phase. From the observation of high-resolution transmission electron microsco py (HRTEM), it has been made clear that the nucleation of amorphizatio n in the alloy occurs on the interface between n-Mg2Ni and Ni regions and progresses toward the inside of the nMg(2)Ni region.