On the influence of crystallographic orientation on superelasticity - Fe-Mn-Al-Ni shape memory alloys studied by advanced in situ characterization techniques

Abstract

The superelasticity of iron-based shape memory alloys is strongly influenced by microstructural features such as crystallographic orientation, size and morphology of grains, character of grain boundaries as well as volume fraction of precipitates. Furthermore, elementary processes such as formation of dislocations, interaction of dislocations with the austenite/martensite phase boundary, and the interaction of different martensite variants result in functional degradation. Advanced in situ characterization techniques like digital image correlation (DIC) and infrared thermography (IR-TG) corroborated by ex situ high resolution electron backscatter diffraction (HR-EBSD) and electron contrast channeling imaging (ECCI) were used to investigate the functional stability of the superelasticity of Fe–Mn–Al–Ni single crystals and oligocrystals under tensile and compressive loading. The early stabilization of martensite during repeated loading was attributed, besides other mechanisms, to the interaction of different martensite variants leading to the formation of dislocations, locally pinning the austenite/martensite interface.