Contact damage evolution in diamondlike carbon coatings on ductile substrates
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A. Bendavid and P.J. Martin Commonwealth Scientific and Industrial Research Organization (CSIRO) Industrial Physics, Lindfield, NSW 2070, Australia
P. Munroe, and M. Hoffman School of Materials Science and Engineering, University of New South Wales, NSW 2052, Australia (Received 17 January 2007; accepted 21 May 2007)
A diamondlike carbon (DLC) thin film was deposited onto a stainless steel substrate using a plasma-enhanced chemical vapor deposition (PECVD) process. Nanoindentation, coupled with focused-ion-beam (FIB) milling, was used to investigate contact-induced deformation and fracture in this coating system. Following initial elastic contact between the coating and the indenter and apparent plastic yield of the substrate, pop-ins were observed in the load–displacement curve, indicative of coating fracture. However, FIB cross-sectional images of indentations revealed the presence of ring, radial, and lateral cracks at loads much lower than the critical load for the first observed pop-ins. Finite element modeling was used, and the properties of the substrate and the film were calibrated by fitting the simulated load–displacement curves to experimental data. Then, based upon the experimental observations of damage evolution in this coating system, the stress distributions relevant to initiate ring, radial, and lateral cracks in the coating were ascertained. Furthermore, the effects of substrate yield stress and coating residual stress on the formation of these cracks were investigated. I. INTRODUCTION
Diamondlike carbon (DLC) coatings have been applied onto surfaces of biomedical implants and computer storage devices in recent years, to take advantage of their high hardness and low coefficient of friction.1 Under certain service conditions, contact stresses can be extremely high. Therefore, it is important to understand the deformation and fracture behavior of DLC coatings. Deformation and fracture of thin films resulting from surface contact depends upon contact geometry, coating thickness and material properties of both the film and the substrate, in particular their elastic and plastic deformation properties. These properties are usually assessed using instrumented indentation.2,3 The use of spherical contacts enable subsequent accurate stress analysis to be undertaken4–7 without the complicating singularities that occur in sharp indentation. One of the major difficulties hindering the understanding of contact deformation behavior of all thin (
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