CRYSTALLOGRAPHICAL ANALYSIS ON MARTENSITE-TRANSFORMATION AND MARTENSITIC MORPHOLOGY

The strain tensor and displacement vector associated with lattice defo rmation were introduced to discuss the effect of self-accommodation an d plastic accommodation in martensitic transformation and the crystall ographic models for {557}(f), {225}(f) and {31015}(f) martensite were proposed, along with their experimental verification. According to the present work, the authors suggest that the invariant habit plane is f ormed by the self-accommodation between different martensite variants with the internal twin substructure, when the strength of parent phase is so high that the plastic accommodation is difficult to occur. Howe ver, when the strength of parent phase is low enough for the plastic a ccommodation to occur, the dislocation substructure in the martensite may be produced, and the invariant habit plane is difficult to form, s o the {225}(f) and {557)(f) habit planes are difficult to be explained by phenomenological crystallographical theory. Furthermore, the autho rs suggest that the martensitic morphology depends on the competition between self-accommodation and plastic accommodation, and also depends on the factors of not only the strength but also the fine structure o f the parent phase. For instance, when the density of crystal defects is high, the dislocation rather than twinned martensite will be introd uced in spite of the very high strength of the parent phase.