Effective γ-surfaces in {111} plane in FCC Ni and L12 Ni3Al intermetallic compound

The well-known concept of γ surfaces originally suggested by Prof. Vitek is extended to the case of a shift of one part of a crystal with respect to the other part in two adjacent {111} planes of a stacking fault. The proposed approach is used to construct the effective γ surfaces in the {111} plane in fcc Ni and L12 Ni3Al of intermetallic compound. It is shown that Ni3Al can have five metastable stacking faults in this plane, namely, an intrinsic superlattice stacking fault, an extrinsic superlattice stacking fault, a complex stacking fault, an antiphase boundary, and a complex extrinsic stacking fault. The existence of the latter in the {111} plane in the L12 Ni3Al intermetallic compound has not been reported previously. The shift of the crystal in two close-packed planes in fcc Ni makes it possible to avoid the formation of a high-energy stacking fault which arises when constructing an ordinary γ-surface, as well as to self-consistently include the extrinsic stacking fault into consideration.