Substrate Effects on the Corrosion Behavior of Tungsten- and Titanium-Doped Diamond-like Carbon Films on 316L Stainless Steel and Ti6Al4V

Abstract

Diamond-like carbon (DLC) films are widely used for corrosion protection, but the same film may perform differently on different substrates. Tungsten-doped (W-DLC) and titanium-doped (Ti-DLC) DLC films were sputtered with the same deposition parameters on 316L stainless steel and Ti6Al4V. The films were characterized by SEM, EDX, water contact angle measurement, and Raman spectroscopy. Their corrosion behavior in 3.5 wt% NaCl was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy. The substrate affected the wettability of Ti-DLC but had little effect on that of W-DLC. It hardly changed the bonding structure of either film. The effective capacitances were too high for insulating barriers. The corrosion current density of each film was also largely independent of the substrate. Both observations indicate that the electrochemical response was governed mainly by the metal-doped film surfaces. As a result, the improvement in corrosion resistance depended on the bare substrate. Both films substantially improved the corrosion resistance of 316L. On Ti6Al4V, Ti-DLC gave only a small improvement, and W-DLC gave no clear benefit. The coatings were therefore most beneficial on 316L, whose passive film is less resistant to chloride attack.