Fig. 5: Microstructure characterization of the secondary phase particles precipitated on I-APT surface in the crevice mouth area and the surface alteration layer of I-APT.

a A SEM image of surface morphology of I-APT in the crevice mouth area (i.e., the band pattern shown in Fig. 1); b A close-up view of a selected area as indicated in a, where large secondary phase crystals are observed; c EDS point analysis conducted on a location as indicated by the red circle in b; d, e A lift-out foil prepared by focused ion beam, which contains a large crystal as shown in b; f A TEM image collected on the crystal from an area as indicated by the red box in e; and g, h Selected area diffraction patterns along two different zone axes, which were acquired from the area shown in f. The surface alteration layer on I-APT exhibited nano-crystalline features as shown in the i a bright-field TEM image and j a dark-field TEM images; and k Electron diffraction ring patterns collected from the alteration layer of I-APT.