Sphere packings as a tool for the description of martensitic phase transformations.

Martensitic transformations which play an important role in metallurgical processes are analysed using group-subgroup relations and sphere-packing considerations. This approach is applied to the transformations between body-centred cubic (b.c.c.) and face-centred cubic (f.c.c.) phases and yields the orientation relations according to the Nishiyama-Wassermann, the Kurdjumov-Sachs and the Pitsch mechanisms. The models proposed by Pitsch and Schrader and by Burgers for the transition between b.c.c. and hexagonally closest-packed (h.c.p.) type structures can be interpreted analogously. In addition, two mechanisms for the transition between cubic f.c.c. and h.c.p. structures are described.