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 (M_s) 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.