Preparation of Al2O3 Gradient Coating on 316L Stainless Steel Substrate

Fe-Al gradient coating was prepared on 316L stainless steel surface by hot-dip aluminizing and high-temperature thermal diffusion.Then the as-prepared aluminized coating was oxygenated by the residual O2 in 98.5%N2.The coating was analyzed by OM,SEM,EDS,XRD,XPS and microhardness.The results show that the average thickness of the coating is 120 μm with good surface after hot dipping at 750 ℃ for 10 min and diffusion at 950 ℃ for 4 h.The coating also had good adherence with the substrate.The surface hardness was up 800-850 HV.Elements of Fe and Al were in gradient distribution.After oxygenating at 900 ℃ for 4 h,oxygen was preferentially combined with aluminium.Alumina was generated by in-situ reaction with a gradient distribution in the oxide film except of the surface.