Improvement of the isothermal oxidation resistance of CoNiCrAlY coating sprayed by High Velocity Oxygen Fuel

Two CoNiCrAlY powders with similar chemical composition and granulometry, but with different starting reactivity toward oxygen, were sprayed by High Velocity Oxygen Fuel (HVOF) onto Hastelloy X superalloy substrates obtaining coatings of comparable thickness. After spraying, samples were maintained at 1000 degrees C in air for different test periods up to 3000 h. Morphological, microstructural, compositional and electrochemical analyses were performed onto the powders and the coated samples in order to assess the high temperature oxidation resistance provided by the different powders. The powder with higher starting reactivity toward oxygen sensibly improves the oxidation resistance of the coated samples by producing thinner and more adherent thermally grown oxide layers in comparison with the other powders.