Correlation between microstructures and mechanical properties in Ni-rich Ni–Mn–Ga high-temperature shape-memory alloys

Microstructures and mechanical properties of polycrystalline and single-crystalline Ni 55+ x Mn 25 Ga 20− x ( x = 1, 2, 3) alloys are investigated. The alloys exhibit a single martensite phase for x = 1, and two phases containing tetragonal martensite phase and face-centered γ phase for x = 2 and 3. The appearance of γ phase can apparently raise the strength and plasticity of the alloys. Moreover, single crystals show better mechanical properties compared with the polycrystals with the same composition. Furthermore, a kind of net-like γ phase is observed in directionally solidified Ni 58 Mn 25 Ga 17 single crystal. This alloy exhibits excellent plasticity due to that the crack propagation is seriously hindered by the plastic net-like γ phase.