Effect of Cr addition on the formation of Fe-Al intermetallic phases in Al2O3/Fe-Al coatings

Al₂O₃/Fe-Al coatings are favored for their excellent comprehensive properties in nuclear fusion power applications. A critical step in fabricating Al₂O₃/Fe-Al tritium-resistant coatings via “aluminizing + oxidation” method is the formation of Fe-Al intermetallic layer on the substrate surface at high temperatures. The present work aims to investigate the influence of chromium (Cr), a prevalent alloying element in Fe-base alloys (such as austenitic stainless steels, RAFM steels) used in fusion reactors, on the formation of Fe-Al intermetallic layers. The Fe-Al phase composition and microstructure of Fe-Cr alloys with different Cr content (0, 9, 19 wt%) were investigated by combinations of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that Cr significantly influences the phase structure and microstructure of Fe-Al intermetallic layers, despite minimal effects on its overall thickness. Cr exists in the form of Cr-rich second phase in Fe₂Al₅, which reduces the transformation rate of an aluminum-rich phase to an iron-rich phase, and also delays the generation of zigzag- or tongue-shaped structure between the intermetallic layer and the substrate, resulting in the formation of a smooth interface.