Coating and near-surface modification design strategies for protective and functional surfaces

This paper discusses strategies for controlling the surface chemistry and microstructure of materials to form protective and functional surfaces through controlled gas-metal reactions. Potential applications range from oxidation, corrosion, and wear resistance to electrochemical devices such as fuel cells to catalysts. Phenomenological examples are presented for coatings designed to self-grade under oxidizing conditions, and for the growth of simple and complex (binary and ternary) nitride and carbide phase surface layers by nitridation and carburization reactions. Specific systems discussed include environmental barrier coatings (EBCs) for Si-based ceramics such as Si3N4 and SiC, the growth of continuous, protective CrN/Cr2N, TiN, VN, NiNbVN, and related simple nitride layers on Fe- and Ni-base alloys, the possible formation of ternary nitride and carbide surface phases (e.g. Ti3AlC2, and related MAX-phases) on intermetallic surfaces to improve oxidation resistance, and the formation of composite near-surface structures in Ag-SiO2 and Co(Mo)-Co6Mo6C2 systems.