Effect of post-deposition shot peening on oxidation resistance of NiCrAlY coatings fabricated by steered cathodic arc evaporation

This study investigates the effect of post-deposition glass bead shot peening on the oxidation resistance of NiCrAlY coatings deposited on CMSX-4 substrates by steered cathodic arc evaporation (CAE). Shot-peened coatings were... [ view full abstract ]

This study investigates the effect of post-deposition glass bead shot peening on the oxidation resistance of NiCrAlY coatings deposited on CMSX-4 substrates by steered cathodic arc evaporation (CAE). Shot-peened coatings were exposed to cyclic furnace testing in air up to 1000oC and their oxidation behavior was compared to that of untreated NiCrAlY samples as well as nickel-aluminide diffusion coatings used as the baseline. The results revealed a substantially reduced oxide weight gain rate of shot-peened samples as compared to those of untreated and baseline coatings. The morphology, elemental and phase compositions of NiCrAlY coatings with and without the shot-peening treatment were analyzed by optical and scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Based on the obtained data it was concluded that the relatively low oxidation resistance of untreated NiCrAlY coatings fabricated by CAE was due to the presence of small particles – microdroplets on their surface. It is believed that these particles promote delamination of the stable alumina and accelerate the formation of nickel-aluminum spinel and non-aluminum oxide scales on the exposed regions of the coating surface after 1500 one-hour cycles. On the contrary, the shot-peened NiCrAlY coatings exhibited a much slower oxide weight gain and showed no signs of alpha alumina spallation after being tested in the same conditions. The enhanced oxidation resistance of shot-peened NiCrAlY samples is explained by the smoothening effect of shot peening on the surface of NiCrAlY coatings fabricated by steered CAE.