Elastoresistance Analysis of NiTi Shape Memory Alloys: Effects of Small Cyclic Strain Along the <001> Austenite Direction

The shape memory effect of NiTi alloys is based on a reversible martensitic transformation, which can be induced by thermal and mechanical driving parameters, and has clear signatures in thermodynamic and transport properties. In this study, we present an elastoresistance analysis of a NiTi shape memory alloy with a Ni concentration of 50.7 at.%. The elastoresistance is sensitive to the complex behavior around the martensitic transformation and deep inside the martensitic phase. We observe rich phenomena, such as different kinds of hysteresis and accumulated resistance changes under cyclic strain, in different characteristic temperature regions related to the phase transformation. A first association to possible mechanisms that lead to elastoresistance effects in materials with a strain-driven phase transformation and a complex transformation-induced microstructure is discussed. Notably, both the single-domain volume properties and the microstructure affect transport properties such as the electrical resistance. Overall, our analysis reveals the power of sensitive resistance measurements combined with uniaxial strain. Future work will help to further isolate different effects.