Effect of atomic order on the martensitic transformation of Ni–Fe–Ga alloys

Abstract

The effect of atomic order on martensitic transformation (MT) temperatures has been studied by differential scanning calorimetry in three polycrystalline alloys with compositions Ni53.5+x–Fe19.5−x–Ga27.0 (x = 0, 0.5 and 1.5). Samples water quenched from different temperatures (470–1070 K) exhibit higher MT temperatures than ones slow cooled from the same temperature. This effect has been ascribed to a decrease of the L21 degree of order of the austenitic phase, which promotes an increase in the MT temperatures in these Ni–Fe–Ga alloys. The differences in ordering with cooling rate have been qualitative confirmed by electron diffraction patterns.