Electronic-structure, corrosion and mechanical properties of nc-CrC/a-C:H films deposited by multi-arc ion plating

Nanocomposite films consisting of a hard nano-crystalline chromium carbide phase and amorphous carbon matrix (nc-CrC/a-C:H) were fabricated using multi-arc ion plating system. The series of films were deposited in various acetylene (C2H2) flow rates ranging from 50 to 150 standard cubic centi-meter per minute (sccm). The ingredient contents, microstructures, corrosion properties, mechanical characteristics and tribological behaviors of the nc-CrC/a-C:H films were investigated carefully as a function of the C2H2 flow rate. X-ray and ultraviolet photoelectron spectroscopies were performed to explain the intrinsic origin of the excellent properties of nc-CrC/a-C:H films from the viewpoint of chemical bonding and electronic-structure. The results showed the films were formed as nano-scale metastable cubic CrC (grain size of 2-10 nm) embedded in the hydrogenated amorphous carbon (a-C:H) matrix. As the flow rate increased, the content of a-C sp(2) increased while the content of CrC decreased. The valence charge transfer at the interface between a-C:H and nc-CrC makes parts of the C-Cr bonds more ionic. The density of such charge transfer was quantified by the C-Cr*/C-Cr ratio. The charge transfer was further verified by the valence band of the films. The results indicated an obvious impact of the density of valence charge transfer on corrosion and mechanical properties. A relatively low density of charge transfer and high work function could result in an enhanced corrosion resistance of the films. A lower vacancies density caused by valence charge transfer could also strengthen the hardness. The change of the density of charge transfer could be attributed to the metallic chromium content in the films. Thus, we can open up a new possible pathway to design the nc-CrC/a-C:H films for applications. (C) 2018 Elsevier B.V. All rights reserved