Invariant line strain theory and its application to the crystallography ofsolid-state phase transformations

The formation mechanisms of the crystallographic features of phase transfor mation, including orientation relationship, habit plane, growth direction a nd transformation strain, are described; the early theoretical studies on t he invariant line strain model are summarized; and the details of a "three- dimensional invariant line strain model" proposed by one of the authors and his colleague abroad are presented. The experimental results on the crysta llographic features of needle-, rod- or lath-shaped precipitates formed in the FCC double left right arrow BCC and HCP double left right arrow BCC pre cipitation transformations were in excellent agreement with the predictions from the model, thus suggesting that the model could well serve as a pheno menological theory of crystallography for diffusion-controlled phase transf ormations.