The behaviour of DLC under high mechanical and thermal load

Hydrogenated amorphous diamond-like carbon (DLC) and silicon doped DLC (Si-DLC) in comparison with other low wear friction coatings and commonly used lubricants were tested in a compression-spin test in order to determine their suitability as substitutes for lubricants in warm massive forming with temperatures up to 700 degreesC. In the compression-spin test a coated, respectively, lubricated punch is pressed and simultaneously rotated in a steel sleeve. Characteristic value is the covered sliding distance, until the coefficient of friction matches a value of 0.3. The temperature was varied between room temperature and 700 degreesC, the rotating speed between 10 and 50 rev./min. At low temperatures up to 300 degreesC lubricants containing molybdenum disulfide show the best results. Also, the sputtered MoS2 coating is very good at low temperatures. DLC presents the best performance of all tested coatings and lubricants at 500 and 700 degreesC and is good at lower temperatures. Si-DLC seems to be only suitable at a temperature of 700 degreesC under the presented load conditions. The covered sliding distance grows for all tested coatings with increasing rotating speed at room temperature. (C) 2003 Elsevier B.V. All rights reserved.