Twin microstructure dependent mechanical response in Ni–Mn–Ga single crystals

Abstract

Ni–Mn–Ga single crystals with a twinning stress of about 0.1 MPa were studied. They showed a tendency to stay in a single variant state and to retain only one or very few twin boundaries during martensite reorientation induced by an external stress or magnetic field. This makes the crystals problematic for application in a magnetic actuator. To solve the issue, we introduced many parallel twin boundaries into the crystals by bending. However, this twin microstructure was not stable under cycling load. Additionally, it exhibited a twinning stress of 0.8 MPa—about ten times higher than a crystal with a single boundary.