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

大多数形状记忆应用都需要各向异性的特性，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，通常需要沿着一定的方向进行优化。镍钛合金和CoNiAl合金是具有优异功能性能和良好耐腐蚀性的形状记忆材料。老化是众所周知的提高这些材料的抗疲劳性能，因为它促进了循环加载条件下的微观结构稳定性。这是由于析出相引起的共调应力和基体硬化所致。在本工程中，采用应力老化促进析出相某些变体的形成，控制内部应力场。采用该方法可获得功能退化程度降低、高温超弹性提高的合金。现在，进一步的研究将集中在理解循环退化对沉淀变体数量的依赖以及变形轴与沉淀习惯面法线之间的角度。所获得的结果将允许形状记忆材料的设计，可以为苛刻的应用量身定制。

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.