Friction and endurance of MoS2/ta-C coatings produced by Laser Arc deposition

The tribological behaviour of MoS2/ta-C double layer coatings deposited by Laser-Arc technology was investigated in vacuum and air. In vacuum environment, the friction coefficient against steel balls varies between 0.005 and 0.02 depending on the contact pressure. At high contact pressures, the friction coefficient is as low as 0.005 and the life time between 340,000 and 500,000 cycles. Furthermore, it is shown that a ta-C base layer improves the performance of MoS2 coating. Surface analyses were performed before and after the tribological tests by means of SEM, EDX, XRD, and TEM. They show that in the top layer beneath the sliding surface crystallization of the initially quasi-amorphous MoS2 took place. TEM images also verified an orientation of the basal MoS2-lattice planes parallel to the surface. ► MoS2/ta-C double-layer coatings were produced by Laser Arc technology. ► The ta-C underlayer has a beneficial effect on both, the wear and the friction behaviour of MoS2. ► Ta-C underlayer provides sufficient low friction and excellent wear resistance in environments where the MoS2 coating fails.► The results indicate very low friction for some coating variants with an endurance up to 500,000 cycles.