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 1 cycle, the subgrain structure is significantly refined, and heterogeneous Σ3 and Σ9 grain boundaries emerge. The low volume and uneven dispersion of the emergent Σ boundaries across the volume show why previous transmission electron microscopy investigations of Σ grain boundary formation were inconsistent.
Bibliographical noteFunding Information:
ANB acknowledges the support provided by the National Science Foundation Graduate Research Fellowship Program (award no. DGE-1057607 ). APS acknowledges support provided by the National Science Foundation (award no. CMMI-1454668 ). ANB and APS acknowledge XSEDE resources (award no. TG-MSS160032 and TG-MSS170002 ). LC and MJM acknowledge support provided by the U.S. Department of Energy Office of Science (award no. DE-SC0001258 ). The MatCI (NSF DMR-1121262) facility at Northwestern University was used for calorimetry. This work is based upon research conducted at the Cornell High Energy Synchrotron Source (CHESS), which is supported by the National Science Foundation under awards DMR-1332208 and DMR-0936384.
- 3D reconstruction
- Coincident lattice
- Grain refining
- Shape memory alloys
- X-ray diffraction