Highly mobile type II twin boundary in Ni-Mn-Ga five-layered martensite

Abstract

Twin relationships and stress-induced reorientation were studied in Ni2Mn1.14Ga0.86 single crystal with five-layered modulated martensite crystal structure. Very low twinning stress of about 0.1 MPa was found for twin boundaries which deviated a few degrees from the (011¯) crystallographic plane. However, twin boundaries oriented exactly parallel to the (011¯) plane exhibited considerably higher level of twinning stress, above 1 MPa. X-ray diffraction experiments and calculations based on approximation of the martensite crystal lattice as a tetragonal lattice with a slight monoclinic distortion identified the two different kinds of twin interfaces as type II and type I twin boundaries.