Al2O3-based hybrid composite coatings for mitigating the slurry erosion of an advanced steel in saline and non-saline environments

The present work focuses on the comparative slurry erosion performance evaluation of an advanced steel (ASME SA387) and the alumina-based hybrid coatings for such steels. The study aims to investigate the effect of coatings' properties on their erosion-corrosion behaviour to comprehend their wear performance in saline and non-saline environments. The coatings have been developed by the highly efficient high-velocity oxygen-fuel (HVOF) process. The alumina matrix is reinforced with ceria (CeO2), and hexagonal boron nitride(hBN). A detailed investigation starts with analyzing the coatings' mechanical properties at surface, subsurface and interface regions by using nanoindentation technique, followed by the slurry erosion performance evaluation. To get an in-depth understanding of the materials' performances, various metallurgical characterization techniques like X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and field emission transmission electron microscopy (FESEM) are used. In saline environments, all the materials eroded more when compared to those in non-saline environments. Corrosion-assisted erosion mechanism is found to be the predominant cause of the higher erosion rates in saline slurry medium. Among the coatings, splat detachment and pitting were found to be the erosive wear mechanisms at 30 degrees and 90 degrees slurry flow directions, respectively. However, erosion reduction of approximate to 90 % at 30 degrees impact angle and approximate to 76 % at 90 degrees impact angles were observed for alumina coatings with 0.8 wt% ceria, and 3 wt% hBN additions when compared to the substrate in the saline environments. The observed results were attributed to the metallurgical enhancements in the form of second phases in the coating microstructure, and the mechanical properties at the surface, subsurface, and interface regions.