SMALL-SCALE TRANSFORMATION BEHAVIOR IN SHAPE MEMORY ALLOYS
Samantha Daly (University of Michigan)
Mechanics of Phase Transforming and Multifunctional Materials
Tue 10:45 - 12:15
CIT 219
In polycrystalline shape memory alloys (SMAs), the role of microstructure on phase transformation is known to be critical to material function. However, the complex interactions between microstructure and transformation are not well understood. Here, we achieve the first full-field quantitative characterization of transformation heterogeneity in SMAs at the microstructural length scale through a novel approach combining digital image correlation, scanning electron microscopy, and electron backscatter diffraction. Stress-induced martensitic phase transformation in polycrystalline Nickel-Titanium, and its relation to the underlying microstructure, is quantitatively examined at the grain level in mechanically loaded tensile samples. The phase front is quite diffuse at the microstructural length scale and progresses in a highly heterogeneous manner, with transformation and plasticity accumulating concurrently and synergistically. Type II-2 twinning is found to be the predominant martensite configuration under these loading conditions, with high bands of strain inside individual grains matched with the orientations of type II-2 twin habit planes to within less than a 1° deviation. Further studies are underway to examine the interaction of plastic slip and martensitic phase transformation.