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