Fig. 7: Schematic representation of the mechanisms of Zr metal to oxide transformation and their effect on the grain morphology and texture of the oxide film based on the orientation of the substrate metal grain.

Two types of oxide microstructure are observed based on the orientation of the substrate grain. a Region 1: a protective oxide layer with long columnar grains and low energy grain boundaries under the influence of the growth stress. b Region 2: less protective oxide, thicker and with more disordered smaller grains. a ZrO, t-ZrO₂, and m-ZrO₂ grains are shown in yellow, orange and green, respectively, and dots indicate stress-driven texture variant; b ZrO, t-ZrO₂ and m-ZrO₂ grains are shown in yellow, orange and green, respectively, where the darker and lighter shade of green indicates the major and minor m-ZrO₂ texture components. The oxide growth direction is marked with an arrow.