The Bonding State and Surface Roughness of Carbon-Doped TiZrN Coatings for Hydrogen Permeation Barriers

We doped carbon into a TiZrN coating to reduce hydrogen permeability, and investigated the phase formation, bonding state, microstructure, and surface roughness of the carbon-doped TiZrN. The laser output for laser carburization was limited to a range of 20-50%. The grain size of the TiZrN coatings decreased from 26.49 nm before carburization to 18.31 nm after carburization. For XPS analysis, the sp²/sp³ ratio was 1.23 at 20% laser output, but it showed 2.64 at 40% laser output, which means that amorphous carbon was formed. As the grain size decreased with the formation of amorphous carbon, the surface microstructure of the carbon-doped TiZrN coatings transitioned to an intergranular structure, indicating the creation of amorphous carbon-embedded (Ti, Zr)(C, N) in the coating. The surface roughness (Ra) of the carbon-doped TiZrN coating was decreased to a maximum of 7.12 nm, and the hydrogen permeability correspondingly decreased by 78% at 573 K.