Thermally controlled shape memory effects in Ni1.95Mn1.42Ga0.63 single crystals

Non-stoichiometric Ni1.95Mn1.42Ga0.63 (at.%) single crystals with 20 mm diameter and 60 mm length were grown by the Bridgman method with a growth rate of 3 mm/h in argon atmosphere. The martensitic transformation starting temperature was obviously increased compared with that of stoichiometric Ni2MnGa. Although the Ni1.95Mn1.42Ga0.63 single crystal exhibited no obvious magnetically controlled shape memory effect along any direction, ∼6.5% of thermally controlled shape memory effect was detected along the c-axis in Ni1.95Mn1.42Ga0.63 single crystal, and the recovery temperature was up to 473 K, making possible its development as a new candidate of high-temperature shape memory alloys. The compressive strength and the fracture strain of single crystal specimens were measured to be 400 MPa and 19%. Based on the microstructure studied by use of both optical microscope and transmission electron microscope, the mechanism of the high-temperature thermally controlled shape memory effect in this alloy is presented in this paper.