LAUSR

Abstract This study reports on the temperature-induced, ambient-air-exposure related structural and morphological evolution of various Al Cr and Al Cr O thin films prepared by cathodic arc evaporation with 20 sccm Ar, 50 sccm O2, or 100 sccm O2 per active source (p.a.s. Detailed cross-sectional scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies are conducted on as-deposited coatings and samples that have been oxidised for 3 h at 900, 1050, and 1200 °C. The high affinity of Al to O promotes the formation of essentially pure α-Al2O3 during oxidation starting between 900 and 1050 °C of the coatings prepared with 20 sccm Ar or 50 sccm O2 p.a.s. and cathodes with Al content ≥50 at.%. However, the Al Cr O coatings prepared with 100 sccm O2 p.a.s. form solid solution α-(Al,Cr)2O3 oxides with Al/Cr ratios according to the used Al Cr cathodes upon thermal exposure to ambient air. The phase composition (prior to oxidation) strongly determines the oxide phase formation. A sufficient intermixing of Al, Cr, and O (with about 60 at.% O) is needed to form α-(Al,Cr)2O3 oxides, otherwise the high affinity of Al to O would rather lead to the formation of Al2O3.