Abstract
Phenomenological calculations have been carried out on the crystallographies of non-thermoelastic and thermoelastic martensitic transformations in Fe–Pt alloys near the composition Fe3Pt, using the theory developed by Wechsler, Lieberman and Read and the crystallographic data recently accumulated. The calculated habit plane normals, directions of the shape strain, and relative twin widths of (112) transformation twins are not greatly different by the type of martensitic transformations. The magnitudes of total shape strain and lattice invariant shear are smaller for the thermoelastic type transformation. Particularly, the normal component of the total shape strain to the habit plane is much smaller for the thermoelastic type transformation roughly by one order of magnitude. The orientation relationship between the austenite and martensite lattices approaches the Nishiyama’s as the transformation becomes thermoelastic. It is thus concluded that the distinct difference between the two types of martensitic transformations exists in the magnitude of the normal component of the total shape strain. This conclusion is also rationalized by a comparison of the thermoelastic Fe-Pt martensite with a non-thermoelastic Fe–Al–C martensite whose crystallographies are very similar to those of the former martensite.
