Development of alumina-based hybrid composite coatings for high temperature erosive and corrosive environments

Low alloy steels are being used for structural applications exposed to extreme environmental conditions such as, high temperature, corrosive and erosive environment in petrochemical industry, turbomachinery, chemical reactors, and nuclear industry. These extreme environment conditions severely affect the performance of critical components. In this context, it is attempted to develop the alumina (Al2O3) based hybrid composite coatings on ASME SA387-22-2 steel to mitigate the effect of high temperature erosion and corrosion. High-velocity oxygen-fuel (HVOF) thermal spray technique is used to develop the coatings. The physical characteristics of the coatings are recorded in terms of density measurement, thermogravimetric analysis, and surface wettability analysis. Hardness and elastic modulus of the coatings are estimated at room temperature using nanoindentation and microhardness at high temperature (400 °C) using Vickers hardness tests. Metallurgical characterization and eroded surface analysis are done using Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy and X-ray diffraction (XRD). High temperature (400 °C) erosion performance of the coatings is recorded using solid particle Air-jet erosion tester. The Corrosion performance of the coatings are analyzed using the potentiodynamic polarization technique and electrical impedance spectroscopy (EIS). Significant improvement in erosion performance (Erosion reduction: ≈ 96% at 30° and ≈63% at 90°) and corrosion resistance (≈92% reduction in corrosion rate) is recorded for the coating reinforced with 0.8 wt% ceria (CeO2) and 3 wt% hexagonal boron nitride hBN as compared to the bare steel. The improved erosive and corrosive characteristics of the coatings are attributed to the refined microstructural aspects, in-situ generation of hard second phases, and induction of hydrophobicity in the composite structure.