The γ-ε Martensitic Transformation : A Model for Stress Induced Variant and its Interaction with Grain Boundary

Abstract
The γ (f.c.c.) to ε (h.c.p.) martensitic transformation occurs through the Shockley a/6<211> faulting every second {111} plane of the f.c.c. structure. A stress induced thin single variant corresponds to a single a/6<2100> faulting vector and leads to a large homogeneous shear (0.35 in amplitude. The tip of such a plate is composed of a set of identical Shockley partial dislocations with large mutual interactions. This work is a presentation of a model which describes the martensite morphology of stress induced ε martensite in shape memory Fe-Mn-Si based alloys. The model includes the formation mechanism of the plate (Seeger' s like) and its growth inside a limited grain. The mutual interaction of Shockley dislocations and their interaction with the grain boundary is semi quantitatively described ; it leads to a lenticular shape of ε martensite thin plates. The model is able to explain the behaviour of this kind of alloys concerning the superelastic effect and the shape memory.