Hot corrosion behaviour of double rare-earth oxides co-doped SrZrO3 coatings in molten sulphate–vanadate salt at 900°C

Abstract

Thermal barrier coatings (TBCs) of Sr(Y0·05Yb0·05Zr0·9)O2·95 (SYYZ) and Sr(Y0·05Gd0·05Zr0·9)O2·95 (SYGZ) were prepared by air plasma spraying. The present study investigated the hot corrosion performance of the SYYZ and SYGZ coatings in the presence of molten Na2SO4+V2O5 salts at 900°C for 10 h. Changes in the coatings were studied using a scanning electron microscope (SEM) to observe the microstructure and X-ray diffraction (XRD) technique to analyse the phase composition. XRD results together with SEM observations indicated that, both the SYYZ and SYGZ coatings reacted with the molten Na2SO4+V2O5 salts at 900°C to form SrSO4, Sr3V2O8, YbVO4 and SrSO4, Sr3V2O8, GdVO4 respectively. The m-ZrO2 was also developed due to the decomposition of both the SYYZ and SYGZ coatings during the corrosion process. The excess Yb2O3 and Gd2O3 in the as sprayed SYYZ and SYGZ coatings respectively, can aggravate the degradation of both the SYYZ and SYGZ coatings by molten Na2SO4+V2O5 salts. The phase transformation and chemical interaction are the main corrosion mechanisms for deterioration of the SYYZ and SYGZ coatings. The YSZ coating was also investigated under the same corrosion condition for comparison.