Fig. 1: Typical nutshell-like microstructure of a solid Fe-Ni metal bleb.

a SEM BSE image and EBSD maps showing the polycrystalline bcc core (with interstitial fcc grains) encased in the single-crystal, plastically deformed, fcc rim. A thin intermediate band (IB) made of tiny bcc and fcc grains is evident between the core and the rim. The grayscale background images are based on the band contrast of EBSD patterns. b Upper hemisphere stereographic pole figures of the measured bcc and fcc orientations for the bleb shown in (a), compared with the crystallographic orientation of the parent fcc grain (red discs) calculated using the ARPGE software²⁴. The overlap of the measured and calculated [111] fcc axes indicates that the bcc grains have formed from a single fcc crystal having the orientation of the present rim. Examples of bow tie patterns and threefold stars are indicated by arrows (see other texts¹¹² for comparison). c Ultra-high resolution TEM ACOM maps showing the crystallographic orientations of the bcc grains in the core and the intermediate band (left), as well as the orientation shared by the retained interstitial fcc grains from the core and the intermediate band, and the plastically deformed fcc rim (right). The grayscale background images reflect the reliability of the TEM diffraction pattern indexing. d STEM bright-field (BF) and high-angle annular dark-field (HAADF) images of the dislocation substructures in the areas framed in (c). A comprehensive and detailed compilation of analogous data collected from the seven blebs investigated in this study can be found in Figs. S3–S5.