Crystallography and morphology of various interfaces in Ti–Ni, Ti–Pd and Ni–Mn–Ga shape memory alloys

Crystallography and morphology of various interfaces in Ti–Ni, Ti–Pd and Ni–Mn–Ga shape memory alloys are investigated by transmission electron microscopy. Neither ledge nor step structures are recognized at the irrational interface of the <0 1 1>B19′ type II twin in Ti–Ni martensite and the <1 2 1>B19 type II twin in Ti–Pd martensite in the two dimensional lattice image from the η1 direction. The combination of plate variants of the 10 and the 14 M Ni–Mn–Ga martensites is subsequently discussed. There are four plate variants commonly designated as A, B, C and D, and three fundamental plate combinations can be identified in a given plate group, namely A: B (C: D) of type II, A: C (B: D) of type I and A: D (B: C) of compound twins in both the martensites. An interesting phenomenon is the migration of A: D boundary in the 10 M martensite during the observation. Finally, we present the atomic structures of {1 1 4}B2 Σ9 boundary in the B2 parent phase of Ti–Ni. The influence of heat treatment atmosphere on the boundary structures is also discussed.