Effect of Al Content on Abnormal Grain Growth and Superelasticity in Fe-Mn-Al-Cr-Ni Shape Memory Alloys with Near-Zero Temperature-Dependence of Transformation Stress

The solvus temperature of face-centered cubic (FCC) phase in Fe-34Mn-xAl-4Cr-7.5Ni (x = 13, 14, and 15) shape memory alloys with different Al contents, and their abnormal grain growth and superelasticity at various temperatures were evaluated. With increasing Al content, the solvus temperature of the FCC phase decreased and the FCC precipitates became finer. Whereas cyclic heat treatment induced abnormal grain growth (AGG) in all samples, large grains were obtained more easily in the alloys with higher Al content. The critical stress for martensitic transformation increased with increasing Al content. The x = 14 alloy is the optimal composition considering grain growth and superelasticity. The newly developed Fe-34Mn-14Al-4Cr-7.5Ni alloy, in which single-crystal can easily be fabricated by AGG, exhibited superelasticity at temperatures ranging from - 263 degrees C (10 K) to 27 degrees C (300 K), with a very small temperature-dependence of the critical stress, comparable to that of conventional Fe-34Mn-13.5Al-3Cr-7.5Ni alloy.

Automated summary

The study evaluated the solvus temperature of the FCC phase in Fe-34Mn-xAl-4Cr-7.5Ni shape memory alloys with varying Al content, as well as their abnormal grain growth and superelasticity at different temperatures. The results showed that increasing Al content led to a decrease in solvus temperature of the FCC phase, finer FCC precipitates, and easier formation of large grains. The newly developed Fe-34Mn-14Al-4Cr-7.5Ni alloy exhibited superelasticity over a wide temperature range with minimal temperature-dependence of critical stress.