Ni 56Mn 25− xCu xGa 19 ( x = 0, 1, 2, 4, 8) high-temperature shape-memory alloys

Abstract

Ni 56Mn 25− x Cu x Ga 19 ( x = 0, 1, 2, 4, 8) alloys were investigated as high-temperature shape-memory alloys (SMAs), with regards to their microstructure, martensitic transformation behavior as well as high-temperature shape-memory effect. These alloys exhibit single martensitic phase with tetragonal structure for x < 2, and dual phases containing martensite and γ phase with fcc structure for x ≥ 2. The peak temperature A p for reverse martensitic transformations increases monotonically from 452.4 °C for x = 0 to 529.9 °C for x = 2 in Ni 56Mn 25− x Cu x Ga 19 ( x = 0, 1, 2, 4, 8) alloys. But when the Cu content is higher than 2 at.%, A p remains almost constant at about 530 °C upon formation of the γ phase. The variations of the martensitic transformation temperatures and shape-memory effects with Cu contents correlate with changes in size factor, electron concentration and precipitation of the γ phase. The introduction of γ phase is helpful to improve the hot workability and ductility of NiMnGa alloy, but deleterious to the shape-memory effect.