Structure and shape memory effect in a Ni54Mn25Ga20Gd1 alloy with a high transformation temperature

Ni54Mn25Ga20Gd1 (at.%) alloy with a high transformation temperature has been obtained by substituting 1 at.% Gd for Ga in a ternary Ni54Mn25Ga21 shape memory alloy. The microstructure and phase transformations in the Ni54Mn25Ga20Gd1 alloy have been investigated by SEM, TEM, XRD and DSC. The results show that the microstructure of the Ni54Mn25Ga20Gd1 alloy consists of matrix and hexagonal Gd (Ni,Mn)4Ga phase, and martensitic transformation start temperature (Ms) is 491 K. The compressive strength and the compressive strain are about 958 MPa and 16%, respectively. The complete recovery is obtained from the Ni54Mn25Ga20Gd1 alloy as the pre-strains are no more than 3%. The maximum shape memory strain is achieved in Ni54Mn25Ga20Gd1 alloy with pre-strain of 4%, and the shape memory strain and recovery ratio are 1.9% and 87.5%, respectively. The two-way shape memory effect is also observed in Ni54Mn25Ga20Gd1 alloy.

► We report the Ni54Mn25Ga20Gd1 shape memory alloy with higher transformation temperatures and better mechanical property compared with Ni54Mn25Ga21.
► The mechanism of toughening has also been revealed.
► The two-way shape memory effect has been observed in Ni–Mn–Ga polycrystalline alloys without training.