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

对于大多数形状记忆应用，各向异性特性是必需的，因此传感器和执行器的材料特性，如形状记忆或超弹性应变，通常需要沿某一方向进行优化。镍钛合金和CoNiAl合金都是形状记忆材料，具有优异的功能性能和良好的耐腐蚀性。众所周知，时效可以提高这些材料的疲劳抗力，因为它提高了循环载荷条件下的组织稳定性。这是由于共格应力和析出物引起的基体硬化所致。在所提出的方案中，利用应力下的时效来促进析出物的某些变体的形成，并控制内部应力场。利用这种方法，可以得到功能退化减少和高温超弹性改善的合金。。进一步的研究将集中于了解循环降解对析出变种数量的依赖以及变形轴与析出习惯面的法线之间的夹角。所获得的结果将使形状记忆材料的设计能够为苛刻的应用量身定做。

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.