Intermittent Deformation Behavior in Epitaxial Ni–Mn–Ga Films

Abstract

This study is conducted to measure intermittent and continuum deformation behaviors in epitaxial Ni–Mn–Ga films under uniaxial tensile loading. First, epitaxial Ni–Mn–Ga film is prepared on a substrate by magnetron sputtering. Secondly, the constraint film is released from substrate by wet-chemical etching of Cr. Thirdly, we simultaneously measure phase transformation band nucleation and strain field arising in epitaxial freestanding Ni–Mn–Ga films. The band nucleations are measured using Stress Drop Analysis (SDA) in macroscopic stress–strain curve, and strain fields are measured using Digital Image Correlation (DIC) method. Results show that smaller size bands nucleated on the beginning stage of stress induced martensite transformation in stress–strain curve, then larger size bands did on the latter stage. The strain field shows macroscopic inhomogeneity under tensile loading. Especially in the latter stage of stress induced martensite transformation in stress–strain curve, the inhomogeneous region propagates along to loading direction although the shape is not distinct. Present Ni–Mn–Ga film microstructure has an order structure with some disorder structures consisting of some martensite arrangements. Their structures will affect intermittent and continuum deformation behaviors in epitaxial Ni–Mn–Ga film.