The Influence of Normal Crack on Detachment of Hard Thin Film

摘要

Recently, hard thin films are often used to improve the tribological performance of machine elements or cutting tools. When the films are subjected to sliding, cracks are often generated by a normal and a friction forces because of the brittle nature of the films. However it has been unknown that whether or not the cracks affect the detachment phenomena of the films from the substrate, which cause drastic deterioration of the sliding surfaces. In this paper a stress analysis of both several hard thin films and the substrates, especially the analysis of the interface between them, is conducted to examine the influence of a crack existing in the film on the detachment of the film. The crack is supposed to be normal to the sliding surfaces since the film thickness is very thin compared to the contact width. A two dimensional FEM method is used for the analysis. The calculated results suggest that the normal crack greatly affects the detachment phenomena of the films under the conditions of high coefficient of friction and thinner film thickness. On the other hand the crack chip is closed and has no influence on the detachment phenomena when the film is thick even if such normal crack is present. The detachment of the film is dependent on the coefficient of friction.