Correlation between Acoustic Emission and Stress Evolution during Single Twin Boundary Motion in Ni–Mn–Ga Magnetic Shape Memory Single Crystal

Abstract

Stress evolution and related acoustic emission (AE) in modulated 10M martensite are simultaneously studied during compression forced motion of Type I and Type II single twin boundary (TB) resulting in microstructure reorientation and large deformation. The single TB of both types is formed in the same sample and traveled the same volume. The single boundary exhibits random jerky movement and for Type I the stress fluctuation can be directly correlated to AE signal. The AE during the single TB motion is an avalanche‐like process surmounting the obstacles – crystal defects. The amplitudes of AE are approximately five times higher for Type I compared to Type II. The energy amplitudes of AE events follow the universal power law with different coefficients for Type I and Type II TB. The peak rate well correlates with stress fluctuation during TB motion. Large differences observed for the same sample indicate a different mechanism of pinning and ultimately a different mechanism of Type I and Type II TB motion.