Reaction, transformation and delamination of samarium zirconate thermal barrier coatings

► The Sm2Zr2O7 coatings transformed from fluorite to pyrochlore upon thermal cycling. ► The coating delamination occurred at the alumina-TGO/mixed zone interface. ► A chemical reaction between SZO and alumina led to the formation of SmAlO3. ► A YSZ layer between TGO and SZO retarded the migration of samaria to the TGO. ► It inhibited the chemical reaction and increased the lifetime of bi-layer coatings.