The plasma nitriding treatment of TiN/TiCN multilayer films

The TiN/TiCN multilayer films were deposited by direct current magnetron sputtering, and then the nitriding treatments were carried out in low pressure plasma excited by single-frequency discharge mode. It could be found that the nitriding time had a considerable influence on the composition of uppermost TiCN layer. These variations mainly embodied on the decrement of the Tisingle bondC bonds and the increment of the Csingle bondN and Tisingle bondN bonds with increasing the nitriding time. Moreover, after the 40 min plasma-nitriding treatment, the TiCN layers within the films produced a mass of amorphous carbon (a-C) due to the decomposition of the supersaturated solid solution, and all TiN layers and the uppermost TiCN layer exhibited fine columnar crystals mixed with some amorphous materials. All the results were attributed to the plasma energy breaking the TiC bonds in the film surface, inducing the structure transformation and supporting the carbon diffusion within the films. In the view of the changes of the structure, the internal stresses and the hardness showed a declining trend slightly. Exhilaratingly, the tribological behaviors of the films were improved significantly by the plasma-nitriding. After 40 min plasma-nitriding, the mean coefficient of friction (COF) and the wear rate of the film sliding 10 h were only about 0.15 and 4.8 × 10−7 mm3/N m, respectively. In addition, the COF of TiN layer fell from around 0.4–0.6 in other films to around 0.15 in this film.