Friction and Wear Mechanisms of Cu/ta-C Coatings Under PAO-4 and PAO-4 with MoDTC Lubrication

The tribological behavior of various types of DLC coatings in formulated and non-formulated lubricants are needed for proper usage of these coatings. In this research, the friction and wear mechanism of four different DLC coatings in poly-alpha-olefin type 4 (PAO-4) with and without MoDTC were investigated using ball-on-disc tribometer. One ta-C (tetrahedral amorphous carbon) and three Cu/ta-C (copper doped ta-C) with different sputter power of 50 W, 150 W, and 200 W coatings were deposited on silicon wafers by using FCVA (filtered cathodic vacuum arc) technique for this research. The results indicate that ta-C coating on silicon wafer has the lowest average friction coefficient (CoF) and better wear resistance than Cu/ta-C coating when lubricated under PAO-4 oil with MoDTC. Cu/ta-C with sputter powers of 150 W and 200 W exhibited the highest average friction coefficient under PAO-4 oil with MoDTC. Meanwhile, the average CoF for all samples were similar under PAO-4 base oil. In terms of wear, ta-C coating showed the highest wear rate under PAO-4 base oil then followed by Cu/ta-C with sputter power of 50 W. Nonetheless, Cu/ta-C with sputter powers of 150 W and 200 W exhibited significantly low wear rate under PAO-4 base oil compared to PAO-4 oil with MoDTC.

Friction and Wear Mechanism Analysis of Polymer Flexible Cable Using a High Natural Frequency Piezoelectric Sensor

The friction and wear of flexible cables are the main factors that cause electrical breakdown and insulation aging, and they greatly reduce the reliability and safety of robots. In order to enhance the reliability and safety of the robot, it is of great necessity to investigate the friction and wear mechanisms of the flexible cable. In this research, the friction and wear mechanisms have been discussed. The effects of relative speed, ambient temperature, and positive pressure on the flexible cables are considered by an orthogonal frictional movement. The cable friction force has been measured by a piezoelectric sensor with high natural frequency characteristics. The relations among friction and different factors affecting friction have also been discussed. The results show that the relative speed and the ambient temperature are the main factors affecting the friction and wear of the cable; the main form of flexible cable wear is mechanical-force chemical friction and wear. Those discoveries will greatly deepen the understanding of the friction and wear mechanisms of flexible cables, and will be beneficial to robot cable-reliability design.