Effects of N-doping on the microstructure, mechanical and tribological behavior of Cr-DLC films

We report on the effects of nitrogen doping on Cr-containing diamond-like carbon (Cr-DLC) films. DLC, Cr-DLC and N-doped Cr-DLC films were deposited on (100) Si substrates using a hybrid plasma-assisted CVD/PVD process. Film microstructure, composition and chemical state of elements were studied using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Mechanical and tribological properties were investigated using microhardness testing and pin-on-disc experiments. Analysis by TEM and XPS shows that the Cr-DLC films contain a dispersion of amorphous, Cr-rich nanoparticles. In the N-doped films, N combines with C and partly transforms the Cr-rich nanoparticles into chromium carbon nitrides, CrC(N), dispersed in the amorphous DLC matrix. Also, a significant portion of N is incorporated into the C network. The N-doped Cr-DLC films were found to possess higher hardness, lower intrinsic stresses and somewhat higher coefficient of friction and wear rate than Cr-DLC and DLC films. Such influence of the N-doping on the properties is attributed to the formation of CrC(N) nanoparticles and C–N bonds in the DLC matrix.