Phase field study on the grain size dependent electrical resistivity-strain response in superelastic nanocrystalline NiTi alloys

The superelastic NiTi alloy's electrical resistivity exhibits significant variations in response to deformation, making it a highly attractive material for sensing applications. However, there exists a lack of comprehensive knowledge of the effects of grain size (GS) on the electrical properties of NiTi alloy. To address this gap, a novel electro-mechanical coupled phase field simulation model is developed, with crucial parameters determined through experimental investigations. The results demonstrate a notable change in the relationship between electrical resistivity and strain, transitioning from a quasi-linear pattern to a piecewise nonlinear one as the GS increases. The observed modification is found to be primarily influenced by the martensitic transformation, characterized by a transition from a uniform mode to a localized mode. As the GS increases, there is an initial drop in the total change of electrical resistivity at peak strain, followed by a subsequent stabilization. This is because the GS, through the stress and the degree of phase transformation, exerts two opposing effects on the variation of electrical resistivity. Furthermore, the combined influence of hysteresis and hysteresis in the martensite fraction contributes to a consistent decrease in resistivity hysteresis as the GS diminishes. This study improves the understanding of how GS affects NiTi alloy's electrical resistivity-strain response and lays the foundation for future sensing performance regulation, expanding its multi-functionality as an intelligent material.