Description
The reversibility of the martensitic phase transformation is crucial for the functionality of shape memory alloys. The easier the martensite is pinned, the faster the degradation of the shape memory alloy occurs during cyclic loading. This study investigates various factors influencing the stabilization of martensite during deformation of single-crystalline states in the FeNiCoAlTi system. Complementary in situ methods, such as digital image correlation and acoustic emission, are used to characterize the evolution of martensitic phase transformation and the role of dislocations during deformation. Thereby, experimental evidence was elaborated pointing at mechanisms that so far have been underrated in terms of functional degradation. In addition, high-resolution electron backscatter diffraction (HR-EBSD) measurements were utilized to identify residual stresses in the austenitic matrix, which significantly contribute to the reverse transformation. Micro-mechanical experiments using pillar compression tests were carried out to study the influence of back stresses on the reversibility of the martensitic phase transformation. The findings from this study foster the understanding of pinning mechanisms during loading of the FeNiCoAlTi shape memory alloy eventually enabling targeted optimization for enhanced superelastic material behavior.
