Tribological properties of hard carbon films on zirconia ceramics

In this study, the authors investigated the tribological properties of hard diamondlike carbon (DLC) films on magnesia-partially stabilized zirconia (MgO-PSZ) substrates over a wide range of loads, speeds, temperatures, and counterface materials. The films were 2 mu m thick and produced by ion-beam deposition at room temperature. Tribological tests were conducted on a ball-on-disk machine with MgO-PSZ balk;, in open air of 30 to 50% relative humidity under contact loads of 1 to 50 N, at sliding velocities of 0.1 to 6 m/s, and at temperatures of 400 degrees C. Al2O3 and Si3N4 balls were also rubbed against the DLC-coated MgO-PSZ disks, primarily to assess their friction and wear performance and to compare it with that of MgO-PSZ balls. A series of long-duration lifetime tests was run at speeds of 1, 2, and 6 m/s under a 5 N load to assess the durability of these DLC films. Results showed that the friction coefficients of MgO-PSZ balls sliding against MgO-PSZ disks were 0.5-0.8 and the average specific wear rates of MgO-PSZ balls ranged from 1 x 10(-5) to 5 x 10(-4) mm(3)/N . m, depending on sliding: velocity, contact load, and ambient temperature. The friction coefficients of MgO-PSZ balls sliding against the DLC-coated MgO-PSZ disks ranged from 0.03 to 0.1. The average specific wear rates of MgO-PSZ balls were reduced by three to four orders of magnitude when rubbed against the DLC-coated disks. These DLC films could last 1.5 to 4 million cycles, depending an sliding velocity. Scanning electron microscopy and micro-laser Raman spectroscopy were used to elucidate the microstructural and chemical nature of the DLC films and worn surfaces.