Wear and Failure Process of TiN and DLC Films Monitored With Open Circuit Potential

The high-hardness ceramic films, such as TiN, DLC, CrN, etc., are characterized by high hardness and superior tribological performance, which are widely used to improve the wear resistance and service life of components. However, some methods for evaluating the tribological performance of the films have some drawbacks on accuracy and sensitivity in the industry application. In this paper, a tribological test is carried out by the ball-on-disk tribometer, combining the three-electrode electrochemical measure system in a 0.9% NaCl solution, and the open circuit potential (OCP) measurement is used to monitor the wear process of the titanium nitride (TiN) and diamond-like carbon (DLC) films. For a single TiN film modified Ti alloy sample, the OCP decreases instantaneously when the TiN film is broken and the substrate is tinily exposed to the solution. However, for the DLC multilayer film, the obvious gradual decrease of the OCP corresponds with the layer-by-layer wear-out failure process of the film. These results show that the OCP of the films is sensitive to the interface condition of the films and the counterpart in the solution. The OCP behaviors of the films can represent the wear and failure process. In other words, the OCP measurement is a reliable and real-time method, which can monitor the wear and failure process of the films.