Investigation of increasing surface hardness of 316L stainless steel using amorphous aluminum phosphate coating

In this study, amorphous aluminum phosphate coating was applied on 316L stainless steel surface to increase hardness and chemical resistance. Amorphous means no crystal structure and grain boundaries due to the lack of weaknesses related to these two parameters. In this synthesis, ethanol-based aluminum nitrate nonahydrate and phosphorus oxide precursor solutions were used. It was heated to 70 ° C for 15 minutes to obtain a clear sol with 75% by weight of aluminum phosphate and a molar ratio of aluminum to phosphorus of 1.75. After activating the surface of steel plates and immersion in aluminum phosphate sol, it was heated in three stages of one minute for 24 hours at 65 ° C and 30 minutes at 500 ° C. Continuous X-RAY diffraction pattern proved the existence of an amorphous structure and showed that it is controlled with some extra aluminum. Scanning electron microscopy images and spectroscopic analysis showed that the peeling of the coating in marble-activated samples was better than that of Aqua-Regia and Loria. The microhardness test on the heat-treated sample at 500 ° C showed a threefold increase in hardness compared to the substrate metal.