Reduced functional degradation in conventional and magnetic shape memory alloys through optimized microstructures

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Anisotropic properties are required for most shape memory applications, therefore material properties for sensors and actuators like shape memory or superelastic strains usually need to be optimized along a certain direction. Nickel Titanium alloys as well as CoNiAl alloys are shape memory materials that exhibit superior functional properties and good corrosion resistance. Aging is well known to improve the fatigue resistance of these materials, as it promotes microstructural stability under cyclic loading conditions. This is due to the coherency stresses and the hardening of the matrix caused by the precipitates. In the proposed project aging under stress is employed to promote the formation of certain variants of the precipitates and control the internal stress fields. Using this approach alloys with reduced functional degradation and improved high-temperature superelasticity were obtained. . The further studies will now focus on the understanding of the dependence of cyclic degradation on the number of precipitate variants as well as on the angle between the deformation axis and the normal to the precipitate habit plane. The results obtained will allow for the design of shape memory materials that can be tailored for demanding applications.