Near-field and far-field high-energy diffraction microscopy and microcomputed tomography X-ray techniques were used to study a bulk single crystal nickel-titanium shape memory alloy sample subjected to thermal cycling under a constant applied load. Three-dimensional in situ reconstructions of the austenite microstructure are presented, including the structure and distribution of emergent grain boundaries. After one cycle, the subgrain structure is significantly refined, and heterogeneous {\Sigma}3 and {\Sigma}9 grain boundaries emerge. The low volume and uneven dispersion of the emergent {\Sigma} boundaries across the volume show why previous transmission electron microscopy investigations of {\Sigma} grain boundary formation were inconsistent.
@article{arxiv.1810.06141,
title = {Three-dimensional in situ characterization of phase transformation induced austenite grain refinement in nickel-titanium},
author = {Ashley N. Bucsek and Lee Casalena and Darren C. Pagan and Partha P. Paul and Yuriy Chumlyakov and Michael J. Mills and Aaron P. Stebner},
journal= {arXiv preprint arXiv:1810.06141},
year = {2018}
}