The Study of High Temperature Oxidation behavior of Different Microstructures of HVOF Thermally Sprayed Coatings

Improvement of thermally sprayed coating properties by microstructure modification has been considered as a significant solution. Therefore, in this research the effect of dissolved oxygen content and post heat treatment on the formation and distribution of secondary phase particles, particularly in nano-scale in the coatings during spraying and after that were studied. Ni-5 wt% Al powders were sprayed by high velocity oxy-fuel (HVOF) technique under two different oxygen/fuel ratios to achieve different melting states for feedstock materials. As-sprayed coatings were exposed to complementary heat treatment including heating at 1100 °C under inert atmosphere, then furnace cooling to room temperature. The as-sprayed and heat treated coatings were evaluated for high temperature performance. Isothermal oxidation tests were carried out at 950 °C for 100 h. The results showed that depending on the spraying conditions and optimization of the coating microstructure, Ni-based sprayed coatings with low Al content could be utilized as an efficient bond coat or overlay coating.