Lattice Softening in Fe3Pt Exhibiting Three Types of Martensitic Transformations.

We have investigated the relation between the softening of elastic constants and martensitic transformation in Fe₃Pt, which exhibits various kinds of martensitic transformation depending on its long-range order parameter S. The martensite phases of the examined alloys are BCT (S = 0.57), FCT1 (S = 0.75, c/a < 1) and FCT2 (S = 0.88, c/a > 1). The elastic constants C' and C₄₄ of these alloys decrease almost linearly with decreasing temperature. Although the temperature coefficient of C' decreases as S increases, C' at the transformation temperature is the smallest in the alloy with S = 0.75, which transforms to FCT1. This result implies that softening is most strongly related to the formation of the FCT1 martensite with tetragonality c/a < 1 among the three martensites. [ABSTRACT FROM AUTHOR]