Hot corrosion behavior of PEO/preceramic polymer dual-layer coating exposed to Na2SO4-NaCl salt

The PEO and PEO/polysilazane-Al2O3 composite coating on Ti6Al4V hot-end components were optimized to investigate the hot corrosion behavior. Results show that PEO coating only defends the matrix from corrosion for a short time. Whereas the dual-layer coating forming a molten salt reacting layer and an alumina- and silicon-enriched glass-like dense Si-N-O barrier layer during the hot corrosion of 800℃ for 240 h, which prevents the inward diffusion of oxygen and corrosive medium to the layer/matrix interface. During exposure, the outer polysilazane-Al₂O₃ layer acts sacrificially, reacting with and consuming molten salt, thereby inhibiting deeper infiltration. Simultaneously, a dense amorphous Si-N-O layer is formed, rich in an Al2O3 skeleton, which effectively prevented the inward diffusion of oxygen, sulfur and chlorine. This multi-layer structure—comprising an outer sacrificial zone, an intermediate amorphous sealant, and an intact PEO inner layer—synergistically protects the substrate via nail-rolling effect and chemical inertness. With minimal mass change and maintained structural integrity, the dual-layer coating shows great potential for long-term thermal protection in extreme environments.