Effect of the metal concentration on the structural, mechanical and tribological properties of self-organized a-C:Cu hard nanocomposite coatings

The influence of the metal content (0-28 at.%) on the structural, mechanical and tribological properties of a-C:Cu films grown by pulsed filtered cathodic arc deposition is investigated. Silicon and AISI 301 stainless steel have been used as substrate materials. The microstructure, composition and bonding structure have been determined by scanning electron microscopy; combined Rutherford backscattered spectroscopynuclear reaction analysis; and Raman spectroscopy, respectively. The mechanical and tribological properties have been assessed using nanoindentation and reciprocating sliding (fretting tests) and have them been correlated with the elemental composition of the films. A self-organized multilayered structure consisting of alternating carbon and copper metal nanolayers (thickness in the 25-50 nm range), whose formation is enhanced by the Cu content, is detected. The nanohardness and Young ́s modulus decrease monotonically with increasing Cu content. A maximum value of the Young's modulus of about 255 GPa is obtained for the metal-free film, whereas it drops to about