Investigation of the phase evolution in a super-elastic NiTi shape memory alloy (50.7 at.%Ni) under extensional load with synchrotron radiation

Inhomogeneous strain distribution associated with stress induced transformation and shear-band formation in super-elastic NiTi is investigated by diffraction with synchrotron radiation and diffraction imaging. We observe a large displacement of the austenite (1 1 0) diffraction peak as a function of tensile strain. This indicates a significant load transfer on residual austenite grains within the martensite matrix of a Lüders-like shear transformation band. A distinct stress state occurs at the interface between the shear-band and the surrounding austenite.