CRYSTALLOGRAPHY OF STRESS-INDUCED B2-]7R MARTENSITIC-TRANSFORMATION IN A NI-37.0 AT PERCENT-AL ALLOY

The crystallography of B2 --> 7R stress-induced martensitic transformation in a Ni-37.0 at%Al alloy was studied using single crystals. The experimental results were compared with predictions of the phenomenological crystallographic theory. The simultaneously measured habit planes and the orientation relationship between parent and martensite showed excellent agreement with the theory, for the lattice invariant shear of faulting on the basal plane. Thus, the phenomenological crystallographic theory was confirmed to apply well to the present B2 --> 7R transformation in the Ni-Al alloy as well, The two transformations B2 --> 7R and B2 --> 3R are compared from the viewpoint of the phenomenological crystallographic theory. By examining the variant selection of the martensite under compression, it is shown that an applied stress interacts with the shape strain upon the present martensitic transformation.