3D Grain Maps of Intragranular Misorientation During Load-Biased Thermal Cycling

It has become increasingly clear over the past decade that local microstructure effects dictate the functional properties and performance of shape memory alloys (SMAs). The ability to spatially resolve and quantify these local microstructure effects at the nano- and microscale will be essential for advancing SMA design. Here, we present a 3D in-situ characterization of a polycrystalline nickel-titanium SMA during load-biased thermal cycling using near-field high-energy diffraction microscopy (nf-HEDM). The measurements include spatially resolved orientation maps, or grain maps, of the austenite phase and show how the intragranular orientation spread of the grains evolves with cycling with 2−5 μm spatial resolution. We discuss how this intragranular misorientation is related to dislocation density and functional fatigue, and we discuss how the evolution of intragranular misorientation varies for different types of grains.