Transmission Electron Microscopy of Twins in 10M Martensite in Ni–Mn–Ga Ferromagnetic Shape Memory Alloy

Abstract

The combination of the 10M martensite plate variants in Ni–Mn–Ga ferromagnetic shape memory alloy was investigated by conventional transmission electron microscopy (CTEM) and electron diffraction experiments. There were 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 {1\\bar{2}\\bar{5}} Type I and A : D (B : C) of {105} compound twins in the martensites. The boundary structure of these twins was also observed in the edge-on state by high resolution electron microscopy (HREM). The boundary of the Type I and the compound twins was not sharp in comparison to that in other shape memory alloys. There were neither ledge nor step structures at the irrational boundary in the Type II twin.