Carbon steel is one of the most widely used engineering materials. While carbon steel alloys have relatively high strength, they exhibit low resistance to oxidation at high temperatures. During oxidation, a porous and non-protective oxide layer formed on the surface, leading to rapid failure of plain carbon steel. One effective solution to combat oxidation is applying a protective layer using thermal spray techniques. Thermal spray coatings, due to their ability to apply various coating materials, can effectively address oxidation and wear issues in steel components. However, these coatings tend to have porosity. Numerous efforts have been made to improve the properties of nickel-aluminum thermal spray coatings, including the use of different thermal spray methods and controlling grain size. These methods are costly, but post-spray heat treatment is a simple and cost-effective solution. Performing heat treatment after the spraying process aims to create a metallurgical bond between the coating and substrate, establish a stable structure, reduce porosity in the coating, enhance oxidation resistance, and extend the service life of steel components. The rationale for using nickel-aluminum coatings includes suitable heat conduction, high resistance to corrosion and oxidation, a high melting point, low density, high creep strength, and low production cost. This study eva‎luates the effect of heat treatment temperature on Ni-5 wt.% Al coatings deposited on St37 steel substrate using flame spray to enhance oxidation resistance. After the spraying process, the coatings were heat-treated at temperatures of 950, 1050, and 1150 ℃ for 1 hour under vacuum conditions. Microscopic examination and energy-dispersive spectroscopy were employed for coating microstructure characterization. Phase analysis was carried out using X-ray diffraction. The results indicate that heat-treated samples exhibit lower porosity compared to untreated samples. Subsequently, samples were subjected to high-temperature oxidation testing, exposed to air at 800 ℃, revealing that heat-treated samples experienced internal oxidation. However, the sample heat-treated at 1050 ℃, due to its lower porosity (10.3%), exhibited less oxidation depth (150 μm) and a narrower region affected by substrate oxidation, compared to other samples. This is in contrast to the untreated sample, where the St37 steel substrate suffered severe oxidation before heat treatment.

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علي اشرفي , حميدرضا سليمي جزي