High temperature oxidation studies of detonation-gun-sprayed Cr3C2–NiCr coating on Fe- and Ni-based superalloys in air under cyclic condition at 900 °C

The cyclic oxidation behavior of detonation-gun-sprayed Cr3C2–NiCr coating on three different superalloys namely Superni 75, Superni 718 and Superfer 800H at 900 °C for 100 cycles in air under cyclic heating and cooling conditions has been investigated in the present work. The kinetics of oxidation of coated and bare superalloys was analysed, using thermogravimetric technique. It was observed that all the coated and bare superalloys obey a parabolic rate law of oxidation. X-ray diffraction, FE-SEM/EDAX and X-ray mapping techniques were used to analyse the oxidation products of coated and bare superalloys. The results on the Cr3C2–NiCr-coated superalloys showed better oxidation resistance due to the formation of a compact and adhesive thin Cr2O3 scale on the surface of the coating during oxidation. The scale remained intact and adherent to the partially oxidised coating during cyclic oxidation due to its good compatibility and similar thermal expansion coefficient between Cr3C2–NiCr coating and the superalloy substrates. In all the coated superalloys, the chromium, iron, silicon and titanium were oxidised in the inter-splat region, whereas splats which consisted mainly of Ni remained unoxidised. The parabolic rate constants of Cr3C2–NiCr-coated alloys were lower than that of the bare superalloys as observed in the present work.