Self-healing behavior of Cr-coated Zr alloy cladding in high temperature steam oxidation process

1Effect of cracks on the oxidation properties of Cr-coated Zr is investigated.2Microstructures of Cr-coated Zr with cracks during oxidation process are analyzed.3Cracks in Cr coatings are self-healed when the temperature increased to 1000 °C.4Cr coatings with cracks can still protect the substrate well in oxidation conditions. Cr-coated Zr alloy claddings, prepared via physical vapor deposition (PVD), were used to study the damage evolution under a series of high-temperature steam oxidation conditions. Through-thickness cracks were initially produced within the Cr coat by internal pressure creep test. The Cr-coated samples with cracks were then oxidized at temperatures from 800 °C to 1200 °C in water steam environment. Microstructures of the samples before and after oxidation were characterized in comparison by scanning electronic microscopy, transmission electronic microscopy and energy dispersion spectrometry. The results showed that a large proportion of cracks would be self-healed when the temperature increased to 1000 °C. At the places where the cracks have survived, the corresponding Zr substrate regions were oxidized to form semi-spherical or fan-shaped ZrO2. However, the maximum depth of ZrO2 under the unhealed cracks was smaller than that of the uncoated claddings at the same oxidation conditions.