A microstructural study and high-temperature oxidation behaviour of plasma sprayed NiCrAlY based composite coatings
Ajit M. Hebbale, М. Р. Рамеш, Jana Petrů, T. V. Chandramouli, M. S. Srinath, Rakshith Kumar Shetty
Abstract
• Three Plasma-Sprayed Coatings Evaluated : The study examined pure NiCrAlY, NiCrAlY + 15% Al₂O₃, and NiCrAlY + 15% YSZ (Yttria-Stabilized Zirconia) coatings on T91 steel substrates. • Superior Oxidation Resistance : All coated samples exhibited considerably better oxidation resistance compared to the uncoated T91 steel substrate, with minimal weight gain and better structural integrity. • Best Performance : The NiCrAlY + 15% YSZ coating performed the best, showing minimal weight gain and superior thermal stability due to the stable YSZ phases acting as effective thermal barriers. • Al₂O₃ Addition Improved Resistance : The NiCrAlY + 15% Al₂O₃ coating exhibited improved oxidation resistance due to the formation of a continuous and protective Al₂O₃ layer. In this study, the development and performance evaluation of plasma sprayed NiCrAlY based coatings, such as NiCrAlY, NiCrAlY + Al₂O₃ and NiCrAlY + YSZ on T91 steel substrates for high temperature applications is carried out. Microstructural features, phase composition and oxidation resistance under cyclic oxidation at 800°C of the coatings were characterized. Analysis of the XRD confirmed the formation of protective phases such as Cr₂O₃, Ni₃Al and NiAl, and the improvement observed in the coating's performance was due to the addition of Al₂O₃ and YSZ. Oxidation resistance was improved for the NiCrAlY + Al₂O₃ coating through the formation of a dense Al₂O₃ oxide layer, but the NiCrAlY + YSZ coating was superior in terms of thermal stability and spallation resistance, because YSZ has low thermal conductivity and high thermal shock resistance. Composite coatings showed improved cyclic oxidation behavior and microstructural analysis revealed reduced porosity and enhanced integrity. The results demonstrate that the addition of Al₂O₃ and YSZ in the NiCrAlY coatings leads to capability of tailoring NiCrAlY–based coatings for high temperature industrial applications with improved durability and oxidation protection.