An interesting oxidation phenomenon of Cr coatings on Zry-4 substrates in high temperature steam environment

• Published in: Corrosion science 2019-08, Vol.156, p.117-124
• Main Authors: Han, Xiaochun, Xue, Jiaxiang, Peng, Shuming, Zhang, Haibin
• Format: Article
• Language: English
• Subjects: Chromium; Coatings; Cr coatings; Diffusion layers; High temperature; High temperature steam oxidation; Oxidation; Oxidation resistance; Reduction of Cr2O3; Substrates; Zircaloys (trademark); Zirconium
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2019.05.017

•An unusual phenomenon during the oxidation of Cr coatings on Zry4 substrates has been discovered.•A new model based on the diffusion and redox reaction of zirconium and chromia layers has been proposed.•Surface morphologies and elemental evolutions in the cross-section of Cr coatings are reported systematically. Cr coatings deposited on zircaloy-4 substrates have been oxidized in high temperature steam environment from 1000 °C to 1200 °C in this study. It has been reported by many authors that Cr coatings have exhibited excellent oxidation resistance in steam environment because of the formation of a dense and adherent Cr2O3 layer on the surface. However, we have found that in the stage when the Cr coating has completely been oxidized and approached the coating-substrate interface, it is reduced by the Zr substrate and mostly transformed into a metallic Cr layer. The mechanisms of oxidation in this stage is therefore more interesting than generally assumed and we have proposed a new model based on the diffusion and redox reaction between Zr and Cr layers in high temperature steam environment.