Mechanistic insights into corrosion processes of RF-sputtered TiMoN coatings through distribution of relaxation time analysis

Abstract

Reactive RF sputtering was used to deposit TiMoN coatings on 304 stainless steel by varying the N2flow while keeping the Ar flow constant. The Nitrogen (N2) flow strongly affected phase evolution, crystallite size, microstructure and electrochemical response, with the coating deposited at Ar:N2= 20:03 showing the optimum combination of mechanical and electrochemical properties. XRD revealed a transition from crystalline to nanocrystalline/amorphous-like structural character at higher N2flow, while plan-view and cross-sectional FESEM showed corresponding changes in surface and cross-sectional morphology. While nanoindentation confirmed the highest hardness and elastic modulus for the 20:03 coating. In 3.5 wt% NaCl, this coating also exhibited the lowest corrosion current density, the highest polarization and charge-transfer resistance and the lowest porosity, indicating superior barrier behavior. Importantly, Distribution of Relaxation Time analysis resolved two dominant relaxation processes and confirmed that the optimized coating suppresses both coating/ electrolyte and defect-controlled interfacial corrosion pathways. The combined electrochemical and microstructural evidence identifies 20:03 as the optimum gas ratio for producing TiMoN coatings with enhanced mechanical integrity and robust corrosion resistance in chloride media.