Abstract
Diamond-like Carbon (DLC) and other hard coatings are used for sliding parts and tools, because of their excellent wear resistance. Even though DLC coatings have a better wear resistance than other coatings, the application of DLC coatings is limited by their low productivity and high cost. The productivity and cost of DLC coatings can be improved by the direct-current plasma-assisted CVD (p-CVD) method and the development of a Si-containing diamond-like carbon (DLC-Si) coating as previously reported by the authors, making DLC more appealing.
The clutch of the JTEKT AWD (All While Drive) electronic control coupling ITCC (Intelligent Torque-Controlled Coupling) requires a high friction coefficient and a high wear resistance, therefore the use of a hard coating would be ideal for such a purpose. In this report, the friction and wear characteristics of a new coating of DLC-Si and hard coatings produced by CVD or PVD are investigated using a traditional ball-on-plate friction tester lubricated in AWD coupling fluid, to examine the application of these coatings to the clutch of the AWD coupling.
As for the hard coatings, the friction coefficients of TiN, CrN and DLC-Si coatings are higher than 0.13 under lubrication in oil. TiN, CrN and a variety of DLC coatings have a higher wear resistance than the non-electrolytic Ni-P coating. Furthermore, note that DLC-Si has a high wear resistance to the counter-sliding part and itself, whereas CrN and TiN have a high aggressiveness to the counterface. Another DLC coating of W containing a diamond-like carbon (W-DLC) coating also has a high wear resistance to the countersurface, however it has a low wear resistance to itself compared with DLC-Si.
Furthermore, DLC-Si has a positive gradient at friction coefficient to sliding speed (µ-v), despite the negative gradient of CrN. The µ-v gradient is a significant property for the clutch to prevent vibration produced by a stick-slip motion. Accordingly, these results suggest that DLC-Si has excellent friction characteristics and is ideal for the clutch coating in AWD coupling fluid.
Keywords:DLC, Diamond-like Carbon, CVD, AWD, Friction