Microstructure of free-standing epitaxial Ni-Mn-Ga films before and after variant reorientation

We investigate the effect of stress-induced reorientation on the martensitic microstructure of free-standing epitaxial Ni-Mn-Ga films. Scanning electron microscopy and high-resolution transmission electron microscopy reveal that the films exhibit coexisting phases of 14 M and NM martensite after release from the MgO(1 0 0) substrate. After superplastic straining the film by 12% by applying tensile stress along a [0 0 1] direction of the Ni-Mn-Ga unit cell, the corresponding crystal structure is identified to be detwinned NM martensite.