Effects of Substrate Bias Voltage on Friction and Corrosion Behavior of Multilayer Ti-DLC Film on the Surface of 316L Stainless Steel

Diamond-like carbon (DLC) films are widely used in the fields of aerospace, metal processing, and marine protection because of their high hardness and excellent wear and corrosion resistance properties. Among them, Ti-doped DLC films have a wide range of applications in the field of surface protection. However, conventional single Ti-doped DLC films are unable to meet the wear and corrosion resistance requirements of harsh marine environments. Thus, the preparation process must be further explored. To promote the application of DLC films in harsh marine environments, Ti / TiN / TiCN / Ti-DLC composite films were prepared on 316 L stainless steel using the medium-frequency magnetron sputtering technique. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were applied to analyze the microscopic morphology, corrosion morphology, and elemental content of the films. The bonding state and chemical composition of the films were analyzed by X-ray photoelectron spectroscopy (XPS). The hardness, tribological behavior, and corrosion resistance of the films were evaluated by a nanoindentation tester, friction and wear tester, and electrochemical testing. The experimental variables are the negative bias voltages of the matrix (-60 V, -80 V, -100 V, and -120 V). The influence of the substrate bias on the structure, mechanical properties, friction properties, and corrosion resistance of the films is highlighted. The results show that the Ti element in the Ti-DLC section mainly exists in the form of TiO2, TiC, and TiCN. The overall thickness of the films deposited at the four different bias voltages is approximately 2 mu m. The thickness of the Ti-DLC section is stabilized in this range of 0.82 +/- 0.03 mu m, which indicates that changes in the substrate bias voltage have little influence on the growth rate of the films. The atomic fraction of the Ti element in the surface layer of all films is approximately 5%, indicating that the change in the substrate bias voltage has little effect on the chemical composition of the film surface. As the substrate bias voltage increased from -60 V to -120 V, the sp3-C / sp2-C ratio, hardness, and elastic modulus also gradually increased. The adhesive force of the films tended to first increase and then decrease, reaching a maximum of 24.5 N at -80 V. Under a normal load of 2 N, the friction factor of all films ranged from 0.24 to 0.32, which is less than that of 316 L stainless steel (0.8). This indicates that the films play a key role in the antifriction and wear resistance. Under a normal load of 7 N, the wear life of the films first increased and then decreased. The wear life was the longest at a bias voltage of -80 V. The anodic polarization curves of 316 L stainless steel and all the films exhibited an obvious passivation phenomenon. The current density to maintain the film passivity is two orders of magnitude lower than that of 316 L stainless steel at -120 V, which shows excellent corrosion resistance. The film resistance Rf and charge transfer resistance Rct gradually increased, indicating that the corrosion resistance of the films gradually improved. The corrosion morphology shows that the main corrosion mechanism of all the films is pitting corrosion. These results show that the design of Ti / TiN / TiCN / Ti-DLC composite films with a combined multilayer structure and Ti-element doping improved the wear resistance and corrosion resistance of 316 L stainless steel and broadened the scope of application of DLC films in marine service environments.