Reduction in EHL Friction by a DLC Coating

This work evaluates the influence of DLC coatings on the frictional behaviour of lubricated line contacts in the fluid friction regime. Experiments on a twin-disc machine showed a significant reduction in friction using DLC coated discs instead of uncoated ones. The experimental results are compared by calculations using a three-dimensional thermal elastohydrodynamic simulation model. According to the calculations, the lower heat conductivity of DLC coatings is the main reason for the reduction in friction. This is because of the higher temperature level in the lubricating gap, which results in a reduction in the effective lubricant viscosity and consequently in reduced frictional shear stress. Lower bulk temperatures of the discs are a further consequence of the low heat conductivity of DLC coatings. The resulting lower temperature at the inlet zone of the contact in the steady-state conditions also leads to larger lubricating gaps and to a further reduction in friction.