High temperature oxidation and hot corrosion behaviors of PEO and PEO/polysilazane preceramic-based dual-layer coatings on Ti6Al4V alloy

Abstract

The high temperature oxidation and corrosion behaviors of a plasma electrolytic oxidation (PEO) coating and a PEO/polysilazane (PEO/PSZ) dual-layer coating are investigated. After exposure in NaCl+Na2SO4 salt at 600 ℃ for 240 h, PEO coating tends to generate porous and loose scales, causing cracking or even complete peeling off from the substrate, and corrosion scales follow the law of formation-shedding-reformulation. After exposure in NaCl+Na2SO4 salt at 600 ℃ for 480 h, the PEO/PSZ coating exhibits a three-layer structure including the outermost corroded layer with sandwich structures, uncorroded Al2O3 particles-containing interlayer, and PEO bottom layer, which retards the continuous penetration of corrosive media and further diffusion of oxygen to the inner bulk alloy, resulting in a remarkable reduction of oxidation and corrosion rate.