ZrO phase embedded in the oxide of Zr-Sn-Nb-Fe-Cr alloy after corrosion

Lath-shaped suboxide was found embedded in the oxide layer located parallel to the metal-oxide interface in the oxide film of Zr-1.0Sn-0.25Nb-0.4Fe-0.2Cr alloy after 300 days exposure. The EDS analysis results revealed that the suboxide phase had a Zr:O ratio approximately equal to 1:1. The TEM diffraction pattern revealed that the structure of the suboxide phase was consistent with the hexagonal ZrO with its lattice parameters a = 0.531 nm and c = 0.320 nm. At the oxide-metal interface of the alloy after 130 days exposure, an independent region of ZrO phase was separated from the ZrO phase bulk by a thin ZrO ₂ oxide slice, which was caused by the selective and preferential oxidation along the subgrain boundaries of the ZrO phase. Finally, a hypothesis was proposed to explain the formation of special location of ZrO phase in the ZrO ₂ oxide.