The　oxidation　behavior　of　Ti-Al-Si-C-N　hard　coatings　with　different　Al　contents　deposited　on　highspeed　steel　and　Si　substrates　by　hybrid　arc-enhanced　magnetron　sputtering　is　investigated　in　the　temperature　range　of　500　degrees　C-1000　degrees　C.　The　coating　hardness　is　maintained　at　around　35　GPa,　and　the　parabolic　oxidation　rate　constant　K-p　at　1000　degrees　C　decreases　to　3.36　x　10(-10)　kg(2)　m(-4)　s(-1)　when　the　Al　concentration　is　increased　to　30　at.　%,　indicating　that　Ti-Al-Si-C-N　coatings　with　larger　Al　concentrations　have　better　oxidation　resistance.　X-ray　diffraction,　cross-sectional　scanning　electron　microscopy,　and　x-ray　photoelectron　spectroscopy　reveal　a　protective　surface　layer　consisting　of　Al2O3,　TiO2,　and　SiO2　that　retards　inward　oxygen　diffusion.　A　mechanism　is　proposed　to　elucidate　the　oxide　formation.　As　a　consequence　of　the　good　oxidation　resistance,　the　Ti-Al-Si-C-N　coatings　have　a　large　potential　in　high-speed　dry　cutting　as　well　as　other　high　temperature　applications.　(C)　2012　American　Vacuum　Society.　[http://dx.doi.org/10.1116/1.4721376]