Abstract

Abstract Factors affecting the appearance of 7~8 wt.% yttria stabilized zirconia thermal barrier coatings were investigated. The coating appearance can be separated into two aspects, darkening and coloring. Coating darkening is related to the retaining of off-stoichiometric zirconium oxide (ZrO2-x) or yttrium oxide (Y2O3-x). These off-stoichiometric oxides are stable at temperatures between 2300 °C and 2700 °C. Rapid cooling of these oxides leads to the retaining of them in the as-sprayed coatings. A heat treatment in air at temperatures higher than 500 °C transforms these off-stoichiometric oxides to stoichiometric oxides and therefore eliminates the coating darkening effect. Coloring of TBCs is attributed to the existence of impurity oxides. Coatings made from the ultra high purity powder, Z204NS, do not exhibit coloring phenomenon before or after heat treatment. As-sprayed coatings made from premium purity (M204NS) or regular purity (A204NS-1) powders exhibit metastable coloring effect. A 1-hour heat treatment at 500 °C can eliminate the metastable colors and turn the coating color back to the color of the starting powder.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.