Structure–Property Correlation of Plasma-Sprayed Inconel625-Al2O3 Bimodal Composite Coatings for High-Temperature Oxidation Protection

Abstract

High-temperature oxidation in coal-fired power stations is a major challenge. Thermal spraying is a prospective surface modification method to deposit protective coatings to combat the severe effects of oxidation at high temperature. Plasma spraying (PS) is a completely developed industrial technique proficient in producing dense coatings on complex-shaped components. In this current investigation, Inconel625-30%Al₂O₃ composite coatings were deposited by varying the size of hard ceramic Al₂O₃ particles (micro-, nano-, and bimodal) in the ductile Inconel625 matrix. The developed composites were evaluated in respect of their microstructural analysis of as-sprayed and oxidized coatings, phase analysis, porosity, and microhardness using various standard techniques. The oxidation tests were executed at a temperature of 900 °C under cyclic conditions to determine the high-temperature oxidation resistance of developed Inconel625-30%Al₂O₃ (micro-, nano-, and bimodal) composite coatings. The coatings after oxidation studies obey the parabolic rate of oxidation and were capable of minimizing the degradation of respective substrate steel against oxidation. In comparison with micro- and nano-forms, the bimodal composition showed superior oxidation resistance. The oxide phases Al₂O_3, Cr₂O₃, TiO_2, and spinel such as NiCr₂O₄ developed during the oxidation process were responsible for the better oxidation resistance of bimodal coatings. The better out-turn of PS bimodal coating was connected with better microstructures and better interactions among micro- and nano-Al₂O₃ reinforcement.