Zlepšení únavových vlastností sliti s tvarovou pamětí NiTi pro jejich širší využitelnost (NiTiUp)

NiTi based shape memory alloys (SMAs) can be potentially used in a wide range of engineering applications exploiting their unique functional properties such as high recoverable strains (~8%) and thermally generated work output (~1 J/g). However, the real application space is largely limited as the fatigue life drops sharply when the full extent of functional properties is required in the application design. Insufficient structural fatigue performance thus represents the key obstacle for upscaling the applicability of NiTi. Though this has been known for over a decade, it was not given appropriate attention in the field. Based on the long term experience in the field, we want to investigate the structural fatigue of Nitinol and NiTi based commercial alloys in all its complexity (experiments using various thermomechanical loading modes, microstructure characterization, modelling). Particular attention will be given to the role of the microstructure evolution, energy dissipation, simultaneous transformation and plasticity, localization of deformation, effect of environment, accumulation of surface damage and reactivity during the fatigue tests. For the scheduled fatigue studies, we want to employ the original in-situ methods (diffraction, electrochemical, infrared imaging) that we recently developed for basic single cycle analysis of martensitic transformations in SMAs. The strategy is to target individual issues listed in the project in separate dedicated experiments and consider them together in final analysis of structural fatigue of NiTi in distinct thermomechanical loading modes.