Elastic Strains Created by the f.c.c. to b.c.c. Martensitic Transformation of Spherical Fe-Co Particles in a Cu Matrix

Abstract

The character and amount of elastic strains created by the f.c.c. to b.c.c. martensitic transformation of small Fe-Co precipitate particles in a Cu matrix were investigated by analyzing moiré fringes in a transmission electron microscope. Taking account of the internally-twinned microstructure of the transformed particles, theoretical evaluation of the elastic strains was made by applying the equivalent inclusion method in micromechanics. From reasonable agreement between the experimentally observed elastic strains and theoretically evaluated ones, it has been concluded that although the internal twinning can partly accommodate the transformation strains, considerable amounts of elastic strains still remain in the as-transformed spherical martensite. This is in contrast to the internally-twinned thin-plate martensite where the accommodation of the transformation strains is considered to be nearly perfect.