Investigation of sputtered carbon and carbon/chromium multi-layered coatings

Abstract Pure carbon and carbon/chromium multilayer coatings were deposited using unbalanced magnetron sputtering technology in a deposition system with a three-fold rotation turntable. The physical properties, microstructure and tribological performance of these coatings were investigated. The pure carbon coating was found to have a hardness of up to 4000 HV whilst the C/Cr multilayer coatings were in general softer with the exact hardness depending on the amount of Cr in the coatings. Keeping the sputtering power of carbon targets constant, a sputtering current on Cr was found that produced coatings with the best combination of properties of hardness of approximately 2200 HV and critical load of scratch ( L c ) up to 85 N. The microstructures of the coatings were analysed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The tribological performance of the coatings was investigated using a pin-on-disc test. The pure carbon coating was found to have very good wear properties at low load whilst the coatings with optimized Cr content were found to have excellent tribological performance at high load. No failure was detected in 1 h running in the pin-on-disc test using a 5 mm WC ball rubbing against a coated M42 steel substrate at a speed of 200 mm/s with a load of 140 N and contact pressure higher than 3.4 GPa. Drilling tests under dry and un-lubricated conditions on C/Cr multilayer coated high-speed steel drills showed very good cutting performance with a lifetime three times longer than that of commercial TiN-coated drills.