KINETICS ON THE MICROLEVEL AND MACROLEVEL IN POLYCRYSTALLINE ALLOY MATERIALS DURING MARTENSITIC-TRANSFORMATION

Kinetics is studied during the martensitic transformation on both the micro- and macro-level from the thermomechanical point of view. A vari ant, a smallest microstructure element in an alloy, is assumed to tran sform at a burst when a transformation condition expressed by means of the driving force is satisfied. It has a micro-fraction showing 1 (tr ansformed) or 0 (yet untransformed). The macrofraction, which represen ts a certain extent of transformation in a representative volume compo sed of a large enough number of variants, is derived by performing an ensemble average of the micro-fraction over the representative volume. The progress of the macro-fraction during thermomechanical loading is shown to be governed by a differential equation, the solution of whic h could be reduced to the conventional transformation kinetics discuss ed in the fields of metallurgy and transformation thermomechanics. A l inear relation is derived between the increments of the macroscopic tr ansformation strain and of the macro-fraction.