Lattice Softening in Fe3Pt Exhibiting Three Types of Martensitic Transformations

Takashi Fukuda,Tomoyuki Kakeshita

doi:10.3390/met7050156

Abstract

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.

Highlights

The relation between softening of elastic constants and martensitic transformation has attracted considerable attention for many years and has been discussed by many researchers [1,2,3,4,5,6,7,8,9,10]
In some alloys exhibiting martensitic transformation, softening of elastic constants C0 = (C11 − C12 )/2 and large elastic anisotropy (C44 /C0 ) was observed in the parent phase, but the significance of the softening is largely different between the alloys
Several kinds of martensite phases appear by slightly changing the composition or long-range order parameter

Summary

Introduction

The relation between softening of elastic constants and martensitic transformation has attracted considerable attention for many years and has been discussed by many researchers [1,2,3,4,5,6,7,8,9,10]. In some alloys exhibiting martensitic transformation, softening of elastic constants C0 = (C11 − C12 )/2 and large elastic anisotropy (C44 /C0 ) was observed in the parent phase, but the significance of the softening is largely different between the alloys. Ti–50.8Ni (at %) [8] and Al–63.2Ni (at %) alloys [4] Because of such a large distribution of C0 at the Ms temperature, the influence of softening of C0 on martensitic transformation is expected to be significantly different between these alloys. We consider that a study on elastic softening in such alloys will help us understand the relation between softening and martensitic transformation

Methods

Results

Conclusion