Triological Performance of Tumbled MOS2 on Biomimetic cBN-TiN Coating

Abstract

cBN-TiN hard composite coatings were prepared by a hybrid deposition technique, i.e., electrostatic spray coating (ESC) followed by chemical vapor infiltration (CVI). The coating surfaces have a biomimetic surface texture of lotus leaf. These surface structures can serve as the reservoirs of solid lubricant particles of MoS2, which have nano and submicron size scales in diameter. The tumbled MoS2 covered the whole cBN-TiN coating surface, leading to a smoother surface (or reduced average surface roughness Ra). Vacuum tribological tests were carried out for both the coatings before and after tumbling. Sliding results suggest that the burnished cBN-TiN coating has a significantly lower coefficient of friction. High temperature sliding tests showed that the effectiveness of the tumbled lubricant layer decreased with increasing testing temperature. Worn coating surfaces and pin scars were characterized by using optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Characterization results show that the tumbled MoS2 layer is responsible for friction reduction during room temperature sliding. This also implies that the biomimetic surface structure is effective for holding the MoS2 solid lubricant particles.