High Velocity Oxy-Fuel Thermally Sprayed rGO Reinforced Alumina-Based Coatings on 17-4 PH Steel: Exploring the Effect of Flame Heat Treatment

The present work focuses on exploring the effect of thermal treatment on HVOF thermally sprayed rGO-reinforced alumina-based coatings on 17-4 PH steel. Based on the previous study, an optimized coating composition (Al₂O₃-0.8CeO₂-0.2 rGO) is selected for exploring the effect of flame heat treatment in terms of physical, tribological, mechanical, and electrochemical properties. The hardness (Vickers and scratch) and tribological responses are recorded using a CETR-UMT tribometer. The as-coated, treated, and worn surfaces are analyzed using Goniometer, Scanning electron microscope (SEM), Energy dispersive spectroscopy (EDS), Raman spectroscopy, and 3-D optical profilometer. Corrosive degradation is studied using Potentiodynamic polarization and Electrical impedance spectroscopy (EIS). The results revealed that the thermal treatment severely deteriorates the coating properties. The Vickers hardness and scratch hardness of the as-sprayed coating were reduced to one-third and one-ninth respectively, after the post-treatment process. The specific wear rate and corrosion rate increased by ≈165 times and ≈1500 times, respectively. Furthermore, the Raman, SEM, and EDS analysis of the corroded region of the heat-treated coating confirmed the formation of iron oxides. This deterioration in the heat-treated coating properties is attributed to the evaporation of the reinforced rGO from the as-sprayed coating making the coating highly porous. So, it is not advisable to heat treat the above-mentioned coating composition above 400 °C.