Thermomechanical material behavior of thin Carbon film under high speed sliding contact
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Micro devices carrying out dynamic motion are susceptible to surface contact during normal operation. To avoid critical friction and wear failures, thin carbon films are widely used as the surface protective coating. However, during high speed sliding contact, carbon films can be thermally degraded by the frictional heat flux, which thus decreases their mechanical/chemical strength. Accordingly, the thermally degraded carbon films can be easily worn out by much lower stress during the following contact. There are typically two types of surface failure for carbon film during high speed sliding contact. One is from a single asperity contact like a deep scratch (or plowing and abrasion). The other is from bulk surface contact like burnishing. Based on those two types of contact, both a single asperity and multi asperity systems are considered in the analytical model. An improved contact model accounting for both asperity and substrate deformation is applied to analyze the thermomechanical contact behavior, while theories of frictional heat generation and heat transfer are used to investigate the change in surface temperature rise on the contact area. In order to accurately estimate the surface temperature rise during the sliding contact between rough surfaces, the thermomechanical analysis with an improved single asperity contact model will be extended to the multi asperity system. Parametric study has been performed to investigate individual and coupling effects of key control parameters on the surface temperature rise during the high speed sliding contact. Novel experiments have been implemented with commercial HDDs to characterize and verify the effect of high speed sliding contact on thermal degradation and material transfer of the hard carbon film. In addition, molecular dynamics simulation has conducted a sliding contact simulation with creating on a diamond carbon like structure to investigate the contact behavior in atomic scale. It was found that severe wear of the hard carbon film would be significantly attributed to thermal degradation of carbon material during its sliding contact. In addition, growth of asperity due to material transfer during the sliding contact was found, and it can be another potential cause of severe damage on the hard carbon film when the growth asperities are exposed to secondary contact in repeated-contact system.