Stress- and Magnetic Field-Induced Martensitic Transformation at Cryogenic Temperatures in Fe–Mn–Al–Ni Shape Memory Alloys

Stress-induced and magnetic-field-induced martensitic transformation behaviors at low temperatures were investigated for Fe–Mn–Al–Ni alloys. The magnetic-field-induced reverse martensitic transformation was directly observed by in situ optical microscopy. Magnetization measurements under pulsed magnetic fields up to 50 T were carried out at temperatures between 4.2 and 125 K on a single-crystal sample; full magnetic-field-induced reverse martensitic transformation was confirmed at all tested temperatures. Compression tests from 10 to 100 K were conducted on a single-crystal sample; full shape recovery was obtained at all tested temperatures. It was found that the temperature dependence of both the critical stress and critical magnetic field is small and that the transformation hysteresis is less sensitive to temperature even at cryogenic temperatures. The temperature dependence of entropy change during martensitic transformation up to 100 K was then derived using the Clausius–Clapeyron relation with critical stresses and magnetic fields.