Describing the morphology of 2H martensite using group theory part I: theory
This paper is devoted to a clear and simple group theory description of the morphology and microstructure (including the orientation relationships among lattice correspondence variants, habit plane variants and the self-accommodation diamond) of 2H martensite in shape memory alloys (SMAs). There are 24 elements in point group P24 of DO3 austenite, and they correspond to 24 habit plane variants. These 24 habit plane variants form a cubic group. Martensite point group P4 is a subgroup of P24 and 4 habit plane variants that correspond to P4 and form a correspondence variant dominant group. A cubic group can be divided into six correspondence variant dominant groups that correspond to six elements of 6 —the left co-set of P4 in P24. The point group S4 is also a subgroup of P24 and is a self-accommodation group in 2H martensite. 4 normal directions of habit plane variants in self-accommodation group S4 cluster together along one  direction. A cubic group can be divided into six self-accommodation equivalent classes, which correspond to six self-accommodation martensite diamonds. There are 4 different cubic groups in 2H martensite. Thus, there are 96 martensite habit plane variants that correspond to 192 normal habit plane directions and 48 phase transformation eigenstrains.