文摘
The ball-on-disk friction and wear tests of CNb>Xb> coatings (CNb>Xb>/CNb>Xb>) were conducted under a nitrogen atmosphere with controlled relative humidity (RH) (3.4–40.0%RH) and oxygen concentration (100–21 × 104 ppm) in this study. We found that the specific wear rate of CNb>Xb> coating on ball (Wb>bb>), which could give stable and low friction coefficient (<0.05), was below 3.0 × 10−8 mm3/Nm. Average friction coefficients (µb>ab>) and Wb>bb> of CNb>Xb>/CNb>Xb> increased (µb>ab>: 0.02–0.33, Wb>bb>: 1.6 × 10−8–2.4 × 10−7 mm3/Nm) with increasing oxygen concentration (230–211,000 ppm) as well as RH (4.7–21.1%RH) under a nitrogen atmosphere. However, the Wb>bb> remained low value below 2.3 × 10−8 mm3/Nm regardless of oxygen concentration (100–207,000 ppm) of a nitrogen atmosphere (3.4–3.9%RH) when CNb>Xb>-coated balls were slid against a hydrogenated CNb>Xb> (CNb>Xb>:H) coatings (CNb>Xb>/CNb>Xb>:H). Besides, the CNb>Xb>/CNb>Xb>:H achieved low and stable friction coefficient below 0.05 under a nitrogen atmosphere (10,000 ppmOb>2b>) regardless of increasing RH up to 20%RH. Raman analysis indicated that the structure of carbon on the top surface of CNb>Xb> coating was changed from as-deposited CNb>Xb> coating in the case of low friction coefficient (<0.05). Furthermore, TOF-SIMS analysis provided the evidence that the carbon derived from CNb>Xb>-coated disk was considered to diffuse into the ball surface, and it mixed with the carbon derived from CNb>Xb>-coated ball on the wear scar, which formed the chemically bonded carbon tribo-layer. Low friction coefficient (<0.05) with CNb>Xb> coatings under a nitrogen atmosphere was achieved due to self-formation of the carbon tribo-layer.
