Investigation Of The Coefficient Of Phase Transformation For Diamond-Like Carbon Films

Surface coating technology is widely used in the engineering. While the matching surface of machine parts are covered with the coatings, their capability of resisting frictional wear will be improved obviously and the service life will be extended Due to the processing technology and materials properties, there must be some defects on the interface of coating and substrate which will cause the failure possibly.The deposition of a diamond-like carbon(DLC) films on Si(100) was performed with the method of Plasma-Activated Chemical Vapor Deposition (PCVD). The thickness and residual stress of the films were measured by step apparatus. Normal distortion of the film was measured by profile apparatus. The experimental results showed that obvious distortion occurred on the surface of Si after deposition and there were high residual stresses in the films. The primary factor leading to the distortion was phase transformation which resulted in the volume expanding during the deposition process. In this paper, a parameter a was defined to describe the change of volume caused by phase transformation. Finite element modeling(FEM) was used to calculate the residual stress and distortion, and then the value of a was worked out. The results of FEM highly agreed to experiment. Results of finite element modeling indicates that the coefficient of phase transformation a could externalize the change of volume after phase transformation reasonably. Analysing the result, we know that the residual stress of the films is affected by both the coefficient of phase transformation and elasticity modulus of films.We analyse the stress states of DLC films with different thickness by using the coefficient of phase transformation. Then, we demonstrate it theoretically that coating materials with smaller a can minish the stress of interface. We can obtain the coefficient of phase transformation by adjusting the experimental parameters. With the introducing and defining of the coefficient of phase transformation, it may be a foundation for optimizing the thickness of films, selecting the materials of films and optimizing the making technique of films.