EXPERIMENTAL ASPECTS OF THE CRYSTALLOGRAPHY OF THE MARTENSITIC TRANSFORMATION OF BCC TO 9R CLOSE-PACKED STRUCTURE.

Abstract

Experimentally observed crystallographic features of the bcc to 9R transformation are compared with the theoretical predictions for the cases of Cu-Al and Cu-Zn alloys. The types of stacking faults and their probabilities of occurrence in the 9R martensites are discussed in detail in relation to the theoretical magnitudes of lattice invariant shear, types of superlattice structures of the parent phases, and the changes in stacking fault energy with the solute content of the alloys. The experimental fact that the faulting of the close-packed layers is not a principal mode of the lattice invariant deformation for the bcc to 3R or 2H transformation, unlike that for the bcc to 9R transformation, is explained from the viewpoint of the phenomenological theory.