Tension/compression asymmetry of functional properties in [001]-oriented ferromagnetic NiFeGaCo single crystals

In the present study the effects of stress state (tension/compression) and test temperature on the critical stress level for the stress-induced martensitic transformation, the shape memory effect and superelasticity of [001]-oriented Ni49Fe18Ga27Co6 (at.%) single crystals were investigated. It is shown that the strong tension/compression asymmetry of the critical stress levels for the stress-induced martensitic transformation can be described by a modified Clausius–Clapreyron relationship, which takes the difference between the elastic moduli of austenite and martensite into account. The temperature interval in which superelasticity occurs and the reversible strain values associated with superelasticity and the shape memory effect are both strongly dependent on the stress state (tension/compression). Moreover, the conditions necessary for the development of high-temperature superelasticity in Ni49Fe18Ga27Co6 single crystals have been determined. For the Ni49Fe18Ga27Co6 single crystals a large interval of superelasticity (315 K < T < 723 K) was obtained when the single crystals were loaded in tension along the [001]-orientation.