Research On Synthesis And Mechanical Properties Of Diamond Like Carbon Multilayer Films

We have developed a new process for building up thick and stable amorphous carbon films with high hardness and low internal stress. It is well known that filtered cathodic vacuum arc (FCVA) deposition is an effective technique for preparation amorphous hard carbon films of high quality. Biasing of the substrate leads to a variation of the ion energy. Therefore the film properties, which are influenced by the ion energy, can be changed over a wide range. Using an alternating high- and low-bias voltage, we have formed hydrogen-free multilayers of hard and soft diamond-like carbon films. The structure and morphology features of diamond-like carbon multilayer films were investigated by X-ray photoelectron spectroscopy (XPS) , Raman spectroscopy and atomic force microscope (AFM) respectively. The hardness of multilayers was measured by Knoop micro-hardness and nanoindentation. The interfacial adhesion was investigated using indentation method. Tribological properties of multilayers in ambient air were investigated using pin-on-disk tribometer. The influence of annealing on the multilayer's structure and properties were studied.The results of XPS and Raman measurement indicated that, the sp~2 content increases with an increase in substrate-bias voltage. The multilayer films have typical diamond-like carbon characteristics. As the increasing of the ratio of soft layer in multiplayer films, the amount of sp~2 bonded carbon cluster increase.The thickness of multilayer film is about 0.5μm. The film has a tendency to be rougher when it is prepared with increased substrate bias voltages. Multilayer films have a smooth surface morphology and show amorphous characteristics.The surface hardness improved greatly after multilayer film deposition. With the increasing of the ratio of soft layer in multilayer films, the micro hardness of multilayers decreased. Compared with the multilayers prepared with dual arcs, the films fabricated with single arc have high hardness (up to 68GPa) and elastic modulus, and become denser and more homogeneous. The interfacial adhesion was improved remarkably by adding a Ti transition layer. Experiment results demonstrated that optimized multilayer films have excellent tribological properties. The friction coefficient of multilayer films against SiC counter-face was only about 0.10.The anneal treatment has little influence on the structure and mechanical properties of the multilayer films. It indicates that the multilayer films have high thermal stability within 400 °C.In general, diamond-like carbon multilayer films with high hardness, good adhesion, low friction efficient and high thermal stability were successively prepared by FCVA technique. Our study suggests that a wide range of application in tribological filed can be extended.