Abstract
The objective of this study is to analyze the effect of a surface nanocrystallization treatment, namely SMAT (Surface Mechanical Attrition Treatment), on a NiTi type shape memory alloy (Ti-50.0 at.% Ni). Initially, an analysis of the thermomechanical behavior and microstructural state of the untreated alloy was conducted. Differential Scanning Calorimetry (DSC) tests were performed to calibrate the heat treatment to be applied to the raw samples. Heat treatments were carried out at different temperature levels and durations to determine an optimal annealing state in terms of phase transformation. This optimum appears to be achieved at a temperature of 700°C for a 2-hour annealing duration.Subsequent thermomechanical characterization tests involving imaging techniques such as infrared thermography and visible imaging were implemented. The measurement of thermal fields, combined with displacement field measurement using image correlation techniques during the tests, allows for the characterization of the phase transformation phenomenon in relation to mechanical response. The objective is to study the influence of the SMAT treatment on the evolution of phase transformations and to evaluate the contribution in terms of mechanical strength of the alloy after nanocrystallization treatment.A detailed microstructural characterization was also carried out before and after the SMAT treatment to study, on the one hand, the influence of such a mechanical treatment on the microstructure of the SMATed NiTi alloy, and on the other hand, its mechanical response. Thus, observations using an optical microscope (OM) and scanning electron microscope (SEM) were performed.This series of characterizations allows for the characterization of the initial state of the microstructure, and the experimental protocol used in this work provides a detailed insight into the thermomechanical properties of the studied alloy.