Enhancement of the corrosion properties by alloying ternary TiAlN coatings with MgGd

This study investigates the corrosion resistance of novel PVD coatings by alloying TiAlN with MgGd. In previous work, MgGd alloying of TiN resulted in outstanding corrosion resistance of up to 1000 h in neutral salt spray (NSS) testing and improved performance in alkaline environments. The corrosion protection was attributed to a combination of hydrophobic surface effects, chemically inert passivation layers, and defect tolerance. To build on these findings, this study extends the alloying concept to ternary TiAlN-based systems. TiAlMgGdN coatings with varying Al/Mg ratios were synthesized and compared with a TiMgGdN reference to evaluate the influence of Al on microstructure, mechanical properties, and corrosion behavior. Characterization was performed using SEM, XRD, and XPS. The chemical composition was determined via GDOES and EDX. Corrosion properties were assessed under neutral, alkaline, and acidic conditions with NSS and potentiodynamic testing. Increasing the Al content led to a reduction in average crystallite size from 15.2 nm to 4.8 nm and an increase in coating hardness from 13.5 GPa to 18.5 GPa. Corrosion potential shifted by +129.7 mV in acidic and +68.9 mV in alkaline media for TiAlMgGdN relative to TiMgGdN. Despite a higher defect density (284 defects/mm vs. 171 defects/mm) and the more noble character, the Al-containing coatings demonstrated superior corrosion resistance. This is attributed to the formation of a chemically stable and protective Al₂O₃ passivation layer that compensates for structural imperfections and limits the ingress of corrosive species. The novelty of this work lies in the first application of the MgGd alloying concept to a TiAlN matrix, demonstrating that the synergistic effects of Al and rare-earth elements significantly enhance both corrosion protection and mechanical performance, particularly in aggressive environments.