Transmission Electron Microscopy (TEM) Study of Twinning in Ni2MnGa

Ni2MnGa is a ferromagnetic shape memory alloy (FSMA). FSMAs exhibit a shape memory effect which is induced through either the application of a magnetic field or mechanical stress. This shape change is reversible through the rotation of the magnetic field or stress. It has been shown that the mechanism for the shape memory response is twin boundary motion; thus, the shape memory response is dictated by the size and orientation of twins within the material. The purpose of this investigation is to study common twinning modes of Ni2MnGa martensite with the 14M structure. Transmission electron microscopy (TEM) samples were made using an electrochemical etching process, and lightand dark-field imaging in combination with selected area electron diffraction was used to identify the type and orientation of twin variants and their interfaces