A comparative investigation of microstructure and high-temperature oxidation resistance of HVOF-sprayed CoNiCrAlY/nano-Al₂O₃ composite coatings using satellited powders

Satellited CoNiCrAlY-Al₂O₃ feedstocks with 2, 4, and 6 wt.% of oxide nanoparticles and pure CoNiCrAlY powder were deposited by the HVOF process on Inconel738 superalloy substrate. Oxidation test was done at 1050 ℃ for 5, 50, 100, 150, 200, and 400 h. Microstructure and phase composition of powders and coatings were characterized by scanning electron microscopy and X-ray diffraction, respectively. The bonding strength of the coatings was also evaluated. The results proved that with the increase in the percentage of nanoparticles (from 2 to 6 wt.%), the amount of porosity (from 1 to 4.7 vol.%), unmelted particles, and the roughness of the coating (from 4.8 to 8.8 µm) increased and the bonding strength decreased (from 71 to 48 MPa). The thickness of the TGO layer of pure coating and composite coatings (2, 4, and 6%) after 400 h oxidation was measured as 6.5, 5.5, 7.6, and 8.1 µm, respectively. The CoNiCrAlY-2% Al₂O₃ coating showed the highest oxidation resistance due to the well-dispersed nanoparticles. The CoNiCrAlY-6% Al₂O₃ coating had the lowest oxidation resistance caused by its rough surface morphology and porous microstructure.