Abstract:Brittleness of traditional Ni-Mn-Ga alloy is a marjor obstacle for its practical applications, as actuators and sensors. The Ni-rich Ni-Mn-Ga alloy can significantly improve the ductility. However, the shape memory strain is significantly reduced. Higher martensitic transformation temperature, good thermal stability and moderate shape memory property are shown in Mn-rich Ni-Mn-Ga. In the present work, microstructural feature, mechanical properties and thermal property of Ni54Mn28+xGa18-x(x=0, 4, 7, 9, 13) were investigated. As the Mn content increases, the γ phase appears, with is a face centered tetragonal (fct) structure, and a γ grain contains a hierarchical "nano-lamellae forming within micro-lamellae" microstructure. A micro-lamella consists of two variants, each variant has a pair of nano-lamellae, and they are {011} twin related. Owing to the introduction of lamellar γ, the ductility is improved. With the increase in Mn content, the compressive stress increases from 914 MPa to 2175 MPa, and the compressive strain increases from 14% to 26%. The martensitic transformation temperature of such series of alloys increases from 352 ℃ to 585 ℃. For Mn-rich Ni-Mn-Ga alloy, the ductility improvement is inferior to that of Ni-rich alloy, but the martensitic transformation temperature is higher.