Effect of Ni substitution for Ga on the polycrystalline Ni-Mn-Ga-Gd high-temperature shape memory alloys

Ni53+xMn25Ga21.9 Gd-x(0.1) (at.%) (x = 0-5) alloys had been obtained by substituting Ga for Ni to increase transformation temperature. The microstructure and phase transformation of polycrystalline Ni53+x-Mn25Ga21.9 Gd-x(0.1) alloys had been investigated by XRD, SEM, TEM and DSC. The results showed that the matrix of Ni53+xMn25Ga21.9 Gd-x(0.1) alloys were tetragonal martensite phase, and the face-centered cubic gamma phase was formed in Ni58Mn25Ga16.9Gd0.1 alloy. The transformation temperatures rose gradually with the increase of Ni content. The compressive fracture strength and strain firstly increased then decreased with the increase of Gd content when Ni content was less than 57 at.%. The generation of ductile gamma phase improved the compressive fracture strength and strain of Ni58Mn25Ga16.9Gd0.1 alloy up to 2327 MPa and 51.7%, respectively. The complete recovery was obtained in Ni53+xMn25Ga21.9 Gd-x-(0.1) (x = 0-3) alloys when the pre-strain was 10%. (c) 2013 Elsevier B.V. All rights reserved.