Analysis of the friction and wear mechanisms of structural ceramic coatings .1. The effect of processing conditions

Experiments were carried out on a wear test machine by means of a thrust-on-washer adapter, where the rotating upper specimen is pressed against a stationary lower specimen. This setup is used to simulate the surface contacts between a carbon steel ring and a chromium nitride coated disk. The changes, of both the mechanical properties and the wear losses of the chromium nitride films produced by cathodic are plasma deposition, were evaluated by varying several controlling factors. The experimental results revealed that either increasing the partial pressure of nitrogen or elevating the substrate bias voltage, helped to both improve the interface adhesive strength and to reduce the coating layer microstructure porosity, thus enhancing the coatings microhardness and leading to great wear loss reductions. The wear losses declined significantly until the CrN layer reached the critical thickness of and then grew again as the thickness was further increased. The roughness of the substrates before coating was strongly related to the wear loss; a smoother surface produced a stronger bonding force, thereby lowering the wear loss. The quantity of unreacted chromium particles and the number of cracks, which could decrease wear resistance, was greatly reduced in the coating layer when the substrate bias voltage was raised up to 175 V.