Influence of the Cooling Rate on Austenite Ordering and Martensite Transformation in a Non-Stoichiometric Alloy Based on Ni-Mn-In

The effect of the melt cooling rate on the atomic ordering of austenite and, as a consequence, on the martensitic transformation of a nonstoichiometric alloy of the Ni-Mn-In system has been studied. In situ TEM observations revealed differences in the mechanism of phase transformations of the alloy subjected to different cooling conditions. It is shown that during quenching a high density of antiphase boundaries (APB) is formed and the alloy is in the austenite-martensitic (10M and 14M) state up to a temperature of 120 K. In a slowly cooled alloy, a lower APB density is observed, and a two-stage transformation, L21/B2 -> 10M -> 14M, occurs in the range of 150-120 K.