Abstract
This thesis focuses on the shape memory alloy NiTi, with a specific emphasis on the influence of the surface nanostructuring process SMAT on its thermomechanical behavior. Through four distinct chapters, it revisits the main characteristics of shape memory alloys (SMAs), highlighting the exceptional properties of the NiTi alloy and exploring the surface nanocrystallization treatment (SMAT). Microstructural characterization is then deeply investigated, particularly by studying the effects of annealing heat treatment and SMAT on phase transition. The third chapter focuses on thermomechanical analysis methods suitable for NiTi, examining tensile tests and nanoindentation. Finally, the fourth chapter analyzes the thermomechanical characterization of the alloy before and after SMAT treatment, highlighting the implications of these transformations on its overall behavior.This thesis contributes to understanding the effects of the SMAT process on the NiTi alloy, revealing links between microstructure, present phases, and mechanical properties. The results offer promising perspectives for better control of the properties of the NiTi alloy.The results obtained for different SMAT treatments show that this process modifies the mechanical response of the material. It also has an influence on its initial state, as illustrated by differences in DSC curves. Kinematic (strain rate fields) and calorimetric (heat source field) measurements also indicate notable differences in responses depending on SMAT processing parameters. Exploration of behavior during load/unload cycles shows a response that stabilizes after a few cycles. Coupling effects seem to be predominant compared to dissipative effects. These observations should be extended to fatigue loading to better highlight any dissipative effects. Similarly, the use of more elaborate interpretation models would allow better consideration of structural effects and enrich the understanding of the relationship between the process and property evolutions.