Research On Mechanical Properties Of Amorphous Si-DLC Films

Diamond like carbon (DLC) films have been extensively studied over the past decades due to their unique combination of properties, such as low friction coefficient, high hardness, high wear resistance and chemical inertness. DLC films have become technologically important materials, used in mechanical applications. But DLC films have some defects and can not be sufficient for special needs in industries. Recently years, the tribological properties of DLC films can be improved by adding other metal or non-metal elements. At present it has been found that, in particular, silicon-incorporated DLC (Si-DLC) films are of significant interest for tribological effects, they possess the potential to improve wear performance in humid atmospheres and at higher temperatures by adding silicon. However, the result showed that the micro-structure and mechanical properties of Si-DLC films were significant affected by adding silicon, but the mechanism is not clear. Therefore, molecular dynamics (MD) simulations and finite element simulations were used from microscopical and macroscopical aspects respectively to study mechanical properties of Si-DLC films such as hardness in this paper.Firstly, three-dimensional structures of Si-DLC films at the density 2.6 g/cm3 by melting and annealing of MD simulations were built, and then the parameters of the mechanical behavior of the Si-DLC films were analyzed. The results show that bulk modulus decreases with the increasing silicon content in the Si-DLC films.Secondly, a diamond indenter was added in the middle above the Si-DLC film, and then the indentation process was completed. The indentation results show that in the approach process, the normal forces change little before the indenter reach the film where the relative height is above zero, and then increase with the indenter getting closer to the film and the relative height decreasing. Besides, the values of the normal forces are above zero, which means that the indenter and films repel each other. While, in the retract process, as the indenter retracts and the relative height increases, the repulsive forces decrease until they become zero. With the addition of silicon, the largest normal force and the pressure decrease until the silicon content of 0.4, and then slightly increase. And the hardness also decreases with an increase in silicon contents, which is in agreement with Papakonstantinou et al.'s result. The pressure in the Si-DLC films is much less compared to that in the DLC film. Finally, ABAQUS was used to build an indentation model to analyze the parameters of the mechanical behavior of the Si-DLC films from the macroscopical aspect. Two indentation simulations (the load and displacement respectively) were carried to study on the hardness of Si-DLC films and get the figures where the silicon content ranging from 0 to 50%. The results of the two methods fit each other very well, both of which show the same tendency as the MD simulations that the hardness decreases with the increasing Si.The conclusions in the paper have a good agreement with the experiments, so they can provide a theory instruction for experimental study of the Si-DLC films, and will promote the application of the Si-DLC films into various industry areas.