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

抄録

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.

Fig. 1 Neutron scattering profiles of MnCoNi and CrCoNi samples measured at room temperature. The results around the forbidden (100)/(110) and fundamental (200) Bragg reflection points are displayed in the left- and right-hand panels, respectively. Filled and open circles denote the result of annealed (673 K, 400 h) and as-quenched MnCoNi samples, respectively. Triangles indicate the result of the annealed (673 K, 400 h) CrCoNi sample. Solid lines represent the results of fits.