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

摘要

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 (551) Type II, A : C (B : D) of (125} Type I and A : D (B : C) of {105 J 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-that in other shape memory alloys. There were neither ledge nor step structures at the irrational boundary in the Type II twin.