Microstructure evolution and degradation mechanisms of amorphous FeCrAlMoSiY coated Zr in 1200 °C steam

Abstract

Herein, structural evolution and degradation mechanisms of the amorphous FeCrAlMoSiY coating during oxidation up to 16 h in 1200 °C steam was studied, using scanning electron microscopy, transmission electron microscopy, x-ray diffractometer, and Raman spectroscopy. The results revealed that no significant oxidation of the Zr substrate occurred within 12 h, which was attributed to the retarded atomic diffusion processes. These processes were achieved through the Al outward diffusion and formation of α-Al2O3 scale, along with the formation of an in-situ Zr2Si-rich diffusion barrier at the coating-substrate interface and the Y2O3 particles segregated at grain boundaries within the coating. Degradation of the coating was primarily due to the destruction of the α-Al2O3 scale by cracks caused by internal oxidation and voids accumulation. These results have implications for understanding the degradation mechanisms and achieving long-term stable protection of the coatings for Zr-based nuclear fuel claddings.