Morphology and crystallography of the isothermal martensite transformation in Fe—Ni—Mn alloys

Abstract

The isothermal martensite transformation in Fe—Ni—Mn alloys has been investigated from a crystallographic viewpoint, because most of the previous work on this type of the transformation has been concerned only with the transformation kinetics and very little is known concerning crystallography. The observed crystallographic features indicate that the invariant-plane strain condition on the habit plane is operative from a very early stage of the transformation, in contradiction with the Olson—Cohen nucleation model. It is proposed that the rate-controlling factor for the isothermal martensite transformation is the thermally activated motion of lattice dislocations in austenite (to relax plastically the shape strain of the martensite plate) and a small dilatation along the habit plane.