Investigating the Effect of Aluminum Oxide Nano-Particles on Microstructure and High-Temperature Oxidation Behavior of HVOF Sprayed MCrAlY Coating

In this research, pure CoNiCrAlY and composite CoNiCrAlY-2, 4 wt% Al2O3 powders were deposited by the HVOF process on IN738 nickel-based superalloy substrates. Composite powders were produced using a water-based solution method and polyvinyl alcohol adhesive to distribute oxide nanoparticles on CoNiCrAlY microparticles. An oxidation test was performed on the coatings at 1050°C and 50, 100, 150, and 200 hours in the stationary air. The microstructure and phase composition of the coatings were investigated by SEM and XRD before and after the oxidation test. The results showed that nanoparticles are present with relatively uniform distribution around the powders and the microstructure of the corresponding coatings. Porosity and surface roughness of pure and composite coatings (2, 4 wt%) were measured as 0.6, 1, and 2.7 vol.% and 4.4, 4.8, and 7.1 µm, respectively. After 200 hours of oxidation test, the thickness of the oxide layer formed on pure and composite coatings (2, 4 wt%) was measured as 5.2, 4.3, and 5.9 micrometers, respectively. CoNiCrAlY coating containing 2 wt% of Al2O3 showed the best resistance to oxidation due to the creation of diffusion barriers by nanoparticles. In contrast, the composite coating containing 4 wt% of Al2O3 had the weakest resistance to oxidation, which was caused by the rough surface morphology and the occurrence of internal oxidation in it.