HVOF Thermal Sprayed Nano-Al2O3 Reinforced MCrAlY Composite Coatings for High Temperature Applications

A novel nanocomposite MCrAlY coating with a fine dispersion of nano-Al2O3 particles were sprayed by high velocity oxygen fuel for high temperature oxidation protections. The presence of Al2O3 nanoparticles could reinforce the metallic MCrAlY coatings, in a similar way to ODS alloys (oxide dispersion strengthening). It could also enhance the oxidation resistance owing to the dispersion of nano-Al2O3 on the surface as nucleation sites, which promotes the early formation of a coherent α-Al2O3 scale. This is essential for an effective protection against oxidation attack, especially for these applications at relatively lower temperatures (<900 °C) with slower growing Al2O3. In this study, a suspension route was employed to achieve a uniform dispersion of 0-10 wt.% Al2O3 nanoparticles with commercial MCrAlY powders. A liquid fuelled HVOF spray gun was used to deposit the nanocomposite MCrAlY-Al2O3 coatings onto nickel based superalloys. The nanocomposite coatings were examined thoroughly by field emission gun scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction analysis. The coated samples were also exposed to isothermal oxidation tests at a range of temperatures to study the effect of nano-Al2O3 on the growth of oxide on the coatings surface. Thermo-gravimetric analysis was performed on free-standing coatings for oxidation kinetics.