Time-Temperature Dependent Short- and Long-Range Structural Transformation in Medium-Entropy Alloys

Neutron scattering experiments were conducted to reveal the origin of diffuse scattering in a medium-entropy alloy (MnCoNi). Results showed that a time-temperature-dependent short-and long-range structural transformation from a face-centered cubic to a primitive tetragonal structure occurs. In the MnCoNi alloy, the long-range ordered phase with a relatively small c/a ratio of 3.7(1)% can only be grown in a limited temperature range, whereas short-range structural transformation with a short correlation length of 1-4 nm can be formed in a wide temperature range. On the contrary, no sign of short -/long-range staggered atomic rearrangement, such as L10 and L12 structures, was observed in the CrCoNi alloy at least at room temperature. The difference in the forming ability of short -/long-range ordering between the MnCoNi and CrCoNi alloys was discussed.