Martensitic transformation behavior of large strain deformed Fe–32% Ni alloy

The martensitic transformation behavior of large strain deformed Fe–32% Ni alloy was investigated by measurement of electrical resistance, X-ray diffraction and transmission electron microscope (TEM) microstructure. The Fe–32% Ni alloy was severely deformed by multi-axial forging at 823 K and a strain rate of 10−3 s−1. The multi-axially forged microstructures are characterized by high dislocation density and non-equilibrium grain boundaries. The large strain deformed alloy was then cooled in liquid nitrogen to cause martensitic transformation. The martensitic transformation starting temperature (Ms) temperature and the volume fraction of martensite decrease with increasing in cumulative strain, and the martensite morphology is characterized by crooked midrib and serrated rim. The analyses show that the high internal stresses, grain refinement and severe lattice distortion hinder the martensite nucleation and growth.