Effect of high vacuum heat treatment on microstructure and cyclic oxidation resistance of HVOF-CoNiCrAlY coatings

After 50 oxidation cycles, a single layer of alumina oxide formed on the as-sprayed coatings with a more uniform thickness compared to a dual-layer oxide of alumina and spinel on the heat-treated coatings. At 260th oxidation cycle, the growth of initiated cracks in previous cycles reached a critical stage which led to spallation of the oxide layer.