Influence of deposition conditions on mechanical and tribological properties of nanostructured TiN/CNx multilayer films

Nanostructured TiN/CNx multilayer films were deposited onto Si (100) wafers and M42 high-speed-steel substrates using closed-filed unbalanced magnetron sputtering in which the deposition process was controlled by a closed loop optical emission monitor (OEM) to regulate the flow of N-2 gas. Multilayers with different carbon nitride (CNx) layer thickness could be attained by varying the C target current (0.5 A to 2.0 A) during the deposition. It was found that the different bilayer thickness periods (i.e. the TiN layer thickness A(TiN) Was fixed at 3.0 nm while the CNx layer thickness Lambda(CNx) was varied from 0.3 to 1.2 nm) significantly affected the mechanical and tribological properties of TiN/CNx, multilayer films. These multilayer films were characterized and analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD), atomic force microscopy (AFM), Rockwell-C adhesion test, scratch test, pin-on-disc tribometer, and nanoindentation measurements. XPS analyses revealed that the chemical states, such as TiN, TiC, TiNxOy and TiO2. existed in a TiN layer. Nanoindentation results showed that the hardness was highly dependent on the bilayer thickness. A maximum hardness of similar to 41.0 GPa was observed in a multilayer film at bilayer thickness Lambda(TiN) = 3.0 nm and Lambda(CNx) = 0.9 nm. All multilayer films exhibited extreme elasticity with elastic recoveries as high as 80% at 5 mN maximum load. The compressive stresses in the films (in a range of 1.5-3.0 GPa) were strongly related to their microstructure, which depended mainly on the incorporation of nitrogen in the films. By scratch and Rockwell-C adhesion tests, the multilayer films with smaller bilayer thicknesses (Lambda(TiN) = 3.0 nm. Lambda(CNx) = 03 and 0.6 nm) exhibited the best adhesion and cohesive strength. The critical load value obtained was as high as similar to 78 N for the films with Lambda(TiN) = 3.0 nm, Lambda(CNx), = 0.9 nm. The friction coefficient value for a multilayer at Lambda(TiN) = 3.0 nm and Lambda(CNx) = 0.9 nm was found to be low 0.11. These adhesive properties and wear performance are also discussed on the basis of microstructure, mechanical properties and tribochemical wear mechanisms. (C) 2008 Elsevier B.V. All rights reserved.