In Situ Synchrotron X-ray diffraction Measurement of Simple Bending of NiTi Shape Memory Alloy Wires

The phase transformation from austensite-to-martensite in austenitic pseudoelastic NiTi shape memory alloy wires have been studied during simple bending using synchrotron X-ray diffraction at room temperature. The compressive nature of the interior curve (intrados) and the tensile nature of the exterior curve (extrados) of the wires have been examined at different angles of bending using both synchrotron X-ray diffraction and scanning electron microcopy. Lattice strains were measured for each phase during bending and mechanical loading, R-phase is also observed during loading. Phase and microstrain mapping in combination with imaging show the localized phase transformation behavior in NiTi shape memory alloy wires during bending. As expected, more surface cracks are observed at the apex of the wire and at higher angles of bending. The results contribute to a better understanding of the bending behavior of austenitic pseudoelastic NiTi shape memory alloy wires.