Orientation dependence and tension/compression asymmetry of shape memory effect and superelasticity in ferromagnetic Co_(40)Ni_(33)Al_(27) Co_(49)Ni_(21)Ga_(30) and Ni_(54)Fe_(19)Ga_(27) single crystals

摘要

In the present study the effects of crystal axis orientation, stress state (tension/compression) and test temperature on shape memory effect and superelasticity of Ni_(54)Fe_(19)Ga_(27)(I), Co_(40)Ni_(33)Al_(27)(II), Co_(49)Ni_(21)Ga_(30)(III) (numbers indicate at.%) single crystals were investigated. The shape memory effect, the start temperature of superelasticity T_1 and the mechanical hysteresis Acr were found to be dependent on crystal axis orientation and stress state. Superelasticity was observed at T_1 =A_f (A_f, reverse transformation-finish temperature) in tension/compression for [00l]-oriented Ni-Fe-Ga crystals and in compression for [00l]-oriented Co-Ni-Ga crystals, which all displayed a small mechanical hysteresis (△σ ≤ 30 MPa). An increase in △σ of up to 90 MPa in the Co-Ni-Al and the Co-Ni-Ga crystals lead to stabilization of the stress-induced martensite, and an increase in to T_1 = A_f + △. The maximal value of △ (75 K) was found in [00l]-oriented Co-Ni-Al crystals in tension. A thermodynamic criterion describing the dependencies of the start temperature of superelasticity T_1 on crystal axis orientation, stress state and the magnitude of mechanical hysteresis is discussed.