High temperature tribological and electrochemical behavior of heat-treated Al₂O₃-base hybrid coating sprayed by HVOF thermal spray technique

Abstract In the present study, the hybrid coating was developed by HVOF over the cast iron substrate. The hybrid coating material comprises Al2O3 (80% w/w) enriched with graphite, MoS2, and fumed silica in w/w of 5%, 10%, and 5% respectively. Microstructure and phase composition of prepared coated samples were analyzed by SEM-EDS, XRD and Raman Spectroscopy. The coated samples were heat-treated and their mechanical, electrochemical and tribological behavior was compared with the as-coated samples. There was a considerable change observed in the micro-hardness and anti-corrosion properties of the coated material after heat treatment. The residual stresses in the heat-treated sample decreased compared to the as-coated sample. The high-temperature tribological investigation was carried out in non-lubricated conditions at three different temperatures 30°C, 150°C, and 300°C with a constant load of 40 N and variable sliding speed. The coefficient of friction and wear rate was calculated and it was found that there was a decrement up to 36% in the wear rate of the heat treated samples compared to the as-coated sample. The SEM morphologies of the wear track showed the presence of small cracks, adhesion, abrasion and smear regions due to plastic deformation.