Kinetics of the sigma-to-alpha phase transformation caused by ball milling in near equiatomic Fe-Cr alloys

Kinetics of the sigma-phase decomposition in three series of sigma-FeCr intermetallic compounds caused by ball milling in a vibratory mill was followed by Mossbauer spectroscopy. It can be described by an exponential decrease with milling time. The decomposition leads to the formation of the alpha-phase as well as that of an amorphous phase. The former is expected from the phase diagram, but the latter is not. The amount of the alpha-phase increases with milling time, reaches a maximum characteristic of the milling conditions, and, finally, after a slow decrease, remains constant. The decrease can be explained in terms of the alpha-phase partial amorphization. The amount of the amorphous phase stays rather constant with a small tendency of increasing for long-term milling times. Its structure seems to evolve with milling time.