Structure-property relations in Cr-C/a-C:H coatings deposited by reactive magnetron sputtering

Amorphous hydrogenated carbon (DLC or a-C:H) coatings have been the subject of intensive research activities within the last two decades due to their superior mechanical and tribological properties. Recently, a nanocomposite concept for severe tribological applications has been proposed, where metal carbides providing enhanced wear resistance are embedded in a lubricating a-C:H matrix. The aim of this work is to investigate coatings based on Cr-C/a-C:H with respect to their structural, mechanical and tribological properties. Coatings in a range of compositions were prepared by reactive unbalanced magnetron (UBM) sputtering from a metallic Cr target in an Ar-CH4 atmosphere. X-ray diffraction and Raman spectroscopy were used to characterize the phase composition of the chromium carbide and a-C:H phases. Dry sliding experiments against different ball counterparts were conducted to determine the friction coefficients. The friction coefficients as well as coating hardness were correlated to different sp(3)/sp(2) a-C:H and chromium carbide fractions within the coatings. The lowest friction coefficients of similar to 0.15 could be obtained for coatings deposited at high CH4 partial pressures. (c) 2005 Elsevier B.V. All rights reserved.