Corrosion behavior of novel Al2O3‒La2O3-based HVOF composite coatings

Corrosion failures in steel components presents a major challenge across various industries, resulting in high maintenance costs and reduced equipment lifespan, particularly in machine parts exposed to humid and saline environments. This study focuses on the development of protective coatings using Al₂O₃ as the base material and La₂O₃ as a reinforcement, with varying weight percentages (1.2%, 1.6%, and 1.8%), applied via high velocity oxy-fuel spraying on stainless steel (SS304) substrates. The corrosion resistance of these coatings was evaluated using a potentiostat in a 3.5% NaCl solution to simulate a harsh saline environment. Electrochemical behavior was analyzed through Tafel, Bode, and Nyquist plots, while electrochemical impedance spectroscopy data were further assessed using the equivalent electrical circuit model method. The experimentation revealed that the S3 coating (98.4% Al₂O₃‒1.6% La₂O₃) exhibited the lowest corrosion rate and highest charge transfer resistance, which depicts its superior corrosion protection. Scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction analyses confirmed the presence of α-Al₂O₃ in the La₂O₃-doped coatings, which plays a crucial role in reducing porosity and improving corrosion resistance. The results obtained in this work demonstrates that the Al₂O₃‒La₂O₃ composite coatings significantly enhances the corrosion resistance of steel.