Preparation of YSZ coated AISI-type 316L stainless steel by the sol-gel coating method and its corrosion behavior in molten carbonate

The effect of heat-treatment conditions on the corrosion behavior of yttria stabilized zirconia (YSZ) coated AISI-type 316L stainless steels in molten carbonate are investigated. YSZ films on stainless steel were prepared by the sol-gel method. While the sample heat-treated at 800°C for 2 hours in air has an uneven surface microstructure with macrocracks, a YSZ coated sample heat-treated in argon has an even microstructure. The polarization resistance and corrosion rate of YSZ coated sample heat-treated in air were deteriorated from 6.948 Ωcm² and 364.7 mpy (millimeter per year) to 3.291 Ωcm² and 769.8 mpy, respectively, by the corrosion for 100 hours due to its poor surface microstructures. At the same experimental condition, meanwhile, those corrosion parameters of YSZ coated sample heat-treated in argon were 15.43 Ωcm² and 164.2 mpy, respectively, and those were improved to 18.83 Ωcm² and 134.6 mpy after the corrosion for 100 hours. This is attributed to the YSZ film with well developed surface microstructures. The concentration profiles of elements and X-ray diffractograms indicate that the oxide layer of YSZ coated sample heat-treated in argon had a triple layer structure composed of outer YSZ film, in between Fe₂O₃ layer, and inner chromium rich layer during corrosion.