Substrate-Dependent Corrosion Behavior of Titanium- and Tungsten-Doped Diamond-Like Carbon Coatings on 316L Stainless Steel and Ti6Al4V

Diamond-like carbon (DLC) coatings are widely used to improve corrosion resistance, but the same coating can behave very differently depending on the metal substrate. This study focuses on how the substrate affects coating performance. Titanium-doped (Ti-DLC) and tungsten-doped (W-DLC) films were deposited by magnetron sputtering using the same process. Both were deposited on two substrates: 316L stainless steel and Ti6Al4V. The coatings were characterized by SEM, EDX, water contact angle, and Raman spectroscopy. Corrosion behavior was evaluated in 3.5 wt% NaCl by poten-tiodynamic polarization and electrochemical impedance spectroscopy (EIS). Wettability shifted in opposite directions on the two substrates: 316L became more hydrophilic after coating, while Ti6Al4V became more hydrophobic. Raman spectroscopy showed that the two dopants produced a similar degree of carbon disor-der on 316L, but diverged on Ti6Al4V. Ti-DLC was the most ordered film of the four coatings and W-DLC formed a more disordered one, suggesting that titanium and tungsten promote carbon ordering differently depending on the substrate. Both films reduced the corrosion current density compared to the bare metal. By EIS, every coated specimen also showed a higher polarization resistance than its bare substrate. On each substrate, Ti-DLC outperformed W-DLC, but with different degrees of improvement. On 316L, the less corrosion-resistant one, gained more from coating in relative terms, while Ti6Al4V reached the highest corrosion resistance. This substrate dependence likely reflects differences in dopant amount and interfacial bonding.