Plasma-sprayed yttria-stabilized zirconia coatings on type 316L stainless steel for pyrochemical reprocessing plant

Abstract

Type 316L stainless steel (SS) is one of the candidate materials proposed for application in pyrochemical reprocessing plants. In the present work, yttria-stabilized zirconia coatings of 300 µm were applied over type 316L SS with a metallic bond coating of 50 µm by an optimized plasma spray process, and were assessed for the corrosion behaviour in molten LiCl-KCl medium at 873 K for periods of 5 h, 100 h, 250 h and 500 h. The as-coated and tested samples were examined by optical microscopy and SEM for homogeneity, penetration of molten salt through coating and corrosion of type 316L SS substrate. The results indicated that the yttria-stabilized zirconia coatings performed well without significant degradation and corrosion attack. Laser melting of the coated samples using CO₂ laser was attempted to consolidate the coatings. The development of large grains with segmented cracks was noticed after laser melting, though the coating defects have been eliminated.