Martensitic transformation, twin boundary and phase interface mobility of directionally solidified Ni-Mn-Ga alloys during compression by EBSD tracing

Abstract

Directionally solidified Ni-Mn-Ga alloy with orderly arrayed austenite and non-modulated martensite (NM) was formed due to microsegregation between dendrite arm and interdendritic region, leading to preferred orientation of <001>A and <110>M coexistence at ambient temperature. The stress-induced martensitic transformation took place due to the increase of martensitic transformation temperature under step-wise uniaxial compression. The detwinning process accompanied with dislocation mobility was easy to carry out on the twin planes 45° inclined to the compression axis, compared with the twin planes parallel to the compression axis in the dominant twinned groups. The martensitic transformation and reorientation of variants were investigated by electron backscatter diffraction.