Structural, mechanical and tribological properties of nanostructured CN_x/TiN multilayers

Nanostructured CN_x/TiN multilayers were deposited onto Si(1 0 0) and M42 high-speed steel substrates using closed-filed unbalanced magnetron sputtering. The deposition process was controlled by a closed-loop optical emission monitor (OEM) to regulate the flow of N₂ gas. Different carbon nitride Λ_CNx layer thicknesses could be attained by varying the C target current (0.5-2.0 A). OEM settings and bilayer thickness periods (i.e. Λ_CNx = 0.3 - 1.2 nm, while Λ_TiN=3.0 nm) significantly affected the mechanical and tribological properties of CN_x/TiN multilayer films. XPS analyses revealed that the chemical states, such as TiN, TiC, TiN_xO_y ???????????and TiO_2, existed in a TiN layer. The nanohardness of the film with bilayer thickness Λ_TiN=3.0 nm and Λ_CNx = 0.9 nm was ∼41.0 GPa. The residual compressive stress was found to be between 1.5 and 3.0 GPa. By the scratch test, the critical load value obtained was high ∼78 N. Rockwell-C adhesion tests exhibited the best adhesion and cohesive strength for multilayers with Λ_TiN=3.0 nm, Λ_CNx = 0.3 and 0.6 nm. The friction coefficient of a multilayer was found to be low 0.11. Lower frictional coefficients and wear rates were the consequences of the increase in Λ_CNx, which provided a lubricating function in the multilayers.