Effect of vacuum heat treatment on the oxidation kinetics of freestanding nanostructured NiCoCrAlY coatings deposited by high-velocity oxy-fuel spraying

In this study, the nanostructured NiCoCrAlY powder feedstock was coated on the substrate via the high-velocity oxy-fuel spraying process. Freestanding nanostructured NiCoCrAlY coatings were then vacuum heat-treated at 1100 °C for 1, 2, and 5 h under a pressure of 10−3 Pa. The microstructure examinations of the nanostructured NiCoCrAlY coatings before and after vacuum heat treatment were investigated using x-ray diffraction and the field-emission scanning electron microscope equipped with electron dispersed spectroscopy analysis. In order to measure the high-temperature oxidation resistance, the freestanding coatings were evaluated using the isothermal oxidation test at 1000 and 1100 °C, respectively, under the air atmosphere. The obtained results showed that homogeneous and adherent α-Al2O3 was successfully formed on the surface of the heat-treated coating during isothermal oxidation. Results also indicated that the heat-treated NiCoCrAlY coating had a higher isothermal and cyclic oxidation resistance. As a consequence, a lower oxide growth rate was achieved by controlling diffusion due to the finer and denser structure of Al2O3 on the heat-treated nanostructured coating for 2 h after the oxidation test.In this study, the nanostructured NiCoCrAlY powder feedstock was coated on the substrate via the high-velocity oxy-fuel spraying process. Freestanding nanostructured NiCoCrAlY coatings were then vacuum heat-treated at 1100 °C for 1, 2, and 5 h under a pressure of 10−3 Pa. The microstructure examinations of the nanostructured NiCoCrAlY coatings before and after vacuum heat treatment were investigated using x-ray diffraction and the field-emission scanning electron microscope equipped with electron dispersed spectroscopy analysis. In order to measure the high-temperature oxidation resistance, the freestanding coatings were evaluated using the isothermal oxidation test at 1000 and 1100 °C, respectively, under the air atmosphere. The obtained results showed that homogeneous and adherent α-Al2O3 was successfully formed on the surface of the heat-treated coating during isothermal oxidation. Results also indicated that the heat-treated NiCoCrAlY coating had a higher isothermal and cyclic oxidation resistance. As...