Self-passivating (Re,Al)B2 coatings synthesized by magnetron sputtering.

(Re0.67Al0.10)B2 and (Re0.74Al0.11)B2 solid solution as well as Re0.85B2 thin films were deposited by hybrid RF-DC magnetron sputtering. X-ray diffraction (XRD) showed that all films exhibit the ReB2 (P63/mmc) crystal structure. X-ray photoelectron spectroscopy (XPS) analyses performed on atmosphere exposed thin film surfaces suggest that ReB2 corrodes, consistent with literature, by forming perrhenic acid (HReO4) already after two days, while (Re0.74Al0.11)B2 forms a self-passivating Al-oxide layer preventing corrosion in a time period ≥ 60 days. Hence, it is evident that Al additions to ReB2 significantly increase the chemical stability during atmosphere exposure.