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Natural grown ZrO2 cannot effectively protect Zr alloy due to the poor phase stability. In this work, a pre-defected ZrO2 coating was fabricated on Zr alloy and further bombarded by Ar8+. A spontaneous martensitic transformation in ZrO2 coating was triggered by lattice distortion and gradient mismatch on the interface. Additionally, Ar8+ bombardment induced the formation of interstitial-vacancy pairs in ZrO2. DFT modeling proved that the interstitial-vacancy pairs were superior in stabilizing T-phase ZrO2, compared with native oxygen vacancies. A mechanism for enhanced corrosion resistance was proposed based on the unique interface and defect state.

The corrosion behavior of Zr alloys was affected by second phases, especially by those containing Fe and Nb. Ti 2 Ni-type (Zr,Nb) 2 Fe compound was melted and exposed to H 2 O 2 water solution at 320 °C and 16.4 MPa for 60 h. The oxide layer was analyzed by X-ray diffraction and high-resolution transmission electron microscope (HRTEM). The formation of nano-crystalline tetragonal ZrO 2 (Fe-rich area) and amorphous ZrO 2 (Fe-deficient area) was observed. HRTEM analysis identified α-Fe could stabilize tetragonal ZrO 2 due to the epitaxial growth. ZrxFeyNb alloys with different iron were melted and corroded similarly. The result was consistent with the proposed mechanism.

C14 Laves phase Zr(Fe,Nb)2 was fabricated and oxidized in a subcritical environment. Electron energy loss spectroscopy was used to study the migration and chemical state evolution of the elements. The oxidation process was accompanied by the formation of multilayered oxide scale, consisting of a crystalline oxide layer, amorphous oxide layer (Fe-poor) and Zr-Nb-Fe-O amorphous layer. The formation of closely bonded, semi-free and metallic iron species as well as the out diffusion of Fe contribute to the multilayered structure growth. The amorphization of the C14 phase occurred with the incorporation of oxygen, which preferentially bonded with Zr and Nb.