  Three-dimensional (3D) X-ray diffraction methods were used to analyze the
evolution of the load-induced rearrangements of monoclinic twin microstructures
within bulk nickel-titanium specimens in 3D and across six orders of magnitude
in length scales: changes in lattice plane spacings and orientations at the
nanoscale, growth and nucleation of martensite twin variants at the microscale,
and localization of plastic strain into deformation bands at the macroscale.
Portions of the localized deformation bands were reconstructed in situ and in
3D. Analyses of the data elucidate the sequence of twin rearrangement
mechanisms that occur within the propagating localized deformation bands,
connect these mechanisms to the texture evolution, and reveal the effects of
geometrically necessary lattice curvature across the band interfaces. The
similarities between shear bands and localized deformation bands in twin
reorientation are also discussed. These findings will guide future researchers
in employing twin rearrangement in novel multiferroic technologies, and they
demonstrate the strength of 3D, multiscale, in situ experiments to improve our
understanding of complicated material behaviors and to provide opportunities to
advance our abilities to model them.
