EFFECT OF AUSTENITE ORDERING ON THE MARTENSITE TRANSFORMATION IN Fe - Pt ALLOYS NEAR THE COMPOSITION Fe3Pt - 1, 2.

The two parts of this paper deal, respectively, with the morphology and transformation characteristics and with the crystallography and general features of the martensite transformation in Fe-Pt alloys with about 25 at. % Pt as affected by austenite ordering. It is shown that austenite ordering results in a progressive change from a ″normal″ burst-type transformation to a thermoelastic one. Despite the marked changes in transformation behavior and kinetics, the transformation crystallography remains essentially unaffected by ordering. It is proposed that the thermoelastic transformation results from the effect of ordering in increasing the matrix elastic limit, and decreasing the chemical free energy change on transformation.