Abstract
New-generation gas turbines require high-performance NiCoCrAlY coatings with superior oxidation resistance. In this study, NiCoCrAlY/nano-CeO2 composite feedstock powders were prepared by the mechanical milling process. Nano-CeO2 modified NiCoCrAlY coatings were then applied using the high-velocity oxy-fuel (HVOF) process. High-temperature oxidation behaviour of the modified coatings was investigated and compared with the conventional coating. Free-standing coatings were subjected to short- and long-term isothermal oxidation testtests at 1000 °C. The microstructural features of the modified powders and coatings before and after oxidation were characterized using the Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive Spectroscopy (EDS), Transmission Electron Microscope (TEM), Raman spectroscopy and X-ray Diffraction (XRD). The oxide growth rate of the coatings was also examined and modeled by the various diffusion-based calculations. Among other types of coatings, the modified NiCoCrAlY-1.0 wt% nano-CeO2 coating had the highest oxidation resistance (26% higher than the conventional NiCoCrAlY coatings). The desired oxidation resistance of the modified NiCoCrAlY-1.0 wt% nano-CeO2 coating attributed to its higher density as well as lower structural porosity and oxide growth rate in both cases of short- and long-term oxidation. Moreover, acceptable conformity of parabolic rate behaviour was obtained for all types of the conventional and modified coatings. The dominant mechanism of oxidation improvement for NiCoCrAlY-1.0 wt.% nano-CeO2 coating was controlling the oxide scale growth rate. The obtained findings indicate that the modified NiCoCrAlY-1.0 wt.% nano-CeO2 coating can be considered as a candidate to protect the hot sections of gas turbines in the future.