ALUMINIDE COATING CHARACTERIZATION ON 304 SS USING SLURRY ALUMINIZING PROCESS

Abstract

The application of aluminide coatings using the slurry aluminizing process has attracted significant attention in industry to enhance the corrosion resistance of structural materials exposed to severe environmental conditions. Nevertheless, several challenges have emerged, including the migration of aluminium from the coating into the substrate and mismatched in the coefficient of thermal expansion (CTE). To address these issues, 304 SS was chosen as the substrate due to its superior compatibility with the coating in terms of CTE. The objective of this project is to investigate the influence of various temperatures and durations on the formation of aluminide coatings containing alumina. The aluminide coating was created through a slurry aluminizing procedure, which involved mixing a slurry composed of 70% Al and 30% Al2O3 with polyvinyl alcohol (PVA). This coating was uniformly applied to the substrate. Subsequently, the coated samples underwent different heat treatment conditions, specifically at temperatures of 650 °C, 680 °C, and 700 °C, for durations ranging from 4 to 10 hrs. Detailed characterization of aluminide coating morphology, energy-dispersive X-ray (EDX), phases, porosity, and corrosion behaviour were evaluated using scanning electron microscope (SEM), X-ray diffraction (XRD), optical microscope (OM) and linear polarization (NOVA 1.7 software). Analysis using energy-dispersive X-ray (EDX) and X-ray diffraction (XRD) techniques revealed the presence of FeAl3 formation at the outermost layer and the development of the FeAl phase within the interdiffusion zone (IDZ). Remarkably, the samples that underwent heat treatment at 700 °C for 10 hours displayed significantly enhanced corrosion resistance. Consequently, the aluminide coating developed on 304 SS, characterized by the presence of the FeAl phase, demonstrates substantial potential for use as an effective protective coating.