The effect of hard coated metals on the thermo‐oxidative stability of a branched perfluoropolyalkylether lubricant

M‐50 and carburized Pyrowear 675® (Carpenter Technology, Reading PA, USA) steel coupons deposited with commercially available physical vapour deposited TiN, TiCN, TiAlCN, TiCrCN/TiB4C multilayer, electroless Ni (E‐Ni) TiN and E‐Ni TiCN coatings were immersed in a branched perfluoropolyalkylether (PFPAE), Krytox AC® (E.I. du pont de Nemours and Company, Wilmington DE, USA), in an oxidative environment at temperatures ranging from 315 to 360 °C for a duration of 24 hours and compared with uncoated coupons. Coated and uncoated Pyrowear 675® coupons demonstrated superior corrosion resistance compared with coated and uncoated M‐50 respectively. The coatings most resistant to chemical attack in the PFPAE fluid were TiCN, E‐Ni TiN and E‐Ni TiCN.