Strain Anisotropy of the Shape Memory in a Single-Crystal Ni49Fe18Ga27Co6 Alloy

Uniaxial stress-strain diagrams of a cubic Ni49Fe18Ga27Co6 single crystal with the shape memory effect have been investigated under successive loads in three directions perpendicular to its faces. The crystal is found to behave radically differently during deformations along the < 110 >(A) and [001](A) directions. At room temperature, the crystal compressed along the [001](A) direction behaves as a superelastic, irrespective of the strain value, whereas under compressions along the < 110 >(A) directions, the superelastic behavior is replaced with shape memory strain at strains of more than 4%. The measured stains in the directions orthogonal to the compression are indicative of anomalous behavior of the Poisson ratio.