Shape memory effects in [001] Ni₅₅Fe₁₈Ga₂₇ single crystal

Shape memory effects in Ni₅₅Fe₁₈Ga₂₇ single crystal grown along the [001] direction by the Czochralski method was studied. It was found that deformation of [001] single crystal in the martensite state was realised via reorientation of 10 M martensite and stress-induced transformations: 10 M → 14 M → L1₀. On unloading, the reverse L1₀ → 14 M → 10 M transformations occurred and a large unelastic strain recovered. On heating, the oriented 10 M martensite transformed to the L2₁ austenite phase and the shape memory effect was observed. An increase in preliminary strain resulted in an increase in the shape memory effect value to 4.6%. The [001] Ni₅₅Fe₁₈Ga₂₇ alloy single crystal demonstrated transformation plasticity and shape memory effects on cooling and heating under stress however, an increase in stress decreased the values of these effects. This was caused by stress-induced martensite appearing in the sample during loading in the austenite state, which decreased the volume of the austenite phase that could undergo the martensitic transformation on cooling. The [001] Ni₅₅Fe₁₈Ga₂₇ alloy single crystal demonstrated a two-way shape memory effect and its value depended on the residual strain in a non-monotonic way and the maximum recoverable strain was 0.7%. (paper)