Design and Investigation of sputtered nanocomposite CrCx/a-C:H low-friction coatings
Research output: Thesis › Doctoral Thesis
The microstructure of nanocomposite PVD coatings composed of metal carbides and amorphous hydrogenated carbon, and thus the mechanical and tribological properties, are strongly related and influenced by the deposition parameters, such as the substrate ion energy or the ion and atom fluxes, respectively. This work investigates and demonstrates these influences on the development and tailoring of a nanocomposite CrCx/a-C:H coating system for severe tribological applications via unbalanced magnetron sputtering (UBM) of a metallic Cr target in Ar + CH4 glow discharges using negative dc bias voltages. Additionally, the thermal stability of these coatings is addressed. Raman spectroscopy and X-ray photoelectron spectroscopy were used to characterize the phase composition and the chemical bonding in the films deposited. The results were correlated to the chemical composition obtained by elastic recoil detection analysis. The coating microstructure was investigated on selected samples by high-resolution transmission electron microscopy combined with electron energy-loss spectroscopy analysis. The nanocomposite coatings can be divided into hard CrCx dominated films, when prepared at low CH4 partial pressure to total pressure (pt) ratios (pCH4/pt <0.4), and into low-friction a-C:H dominated films, when prepared at pCH4/pt > 0.4. The structure of the nanocomposite coatings consists of 2-10 nm sized fcc CrC crystallites embedded in a Cr containing a-C:H matrix.