Effect of substrate roughness on the contact damage of thin brittle films on brittle substrates |
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Authors: | Mirko Weidner,Oscar Borrero-Ló pez,Mark Hoffman,Avi Bendavid |
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Affiliation: | a School of Materials Science and Engineering, University of New South Wales NSW 2052, Sydney, Australia b Institute for Materials Science, Technische Universität Darmstadt, Petersenstrasse 23, 64287 Darmstadt, Germany c Departamento de Ingeniería Mecánica, Energética y de los Materiales, Universidad de Extremadura, 06071, Badajoz, Spain d CSIRO Materials Science and Engineering, P.O. Box 218, Lindfield NSW 2070, Australia |
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Abstract: | The effect of substrate and surface roughness on the contact fracture of diamond-like carbon coatings on brittle soda-lime glass substrates has been investigated. The average surface roughness (Ra) of the examined samples ranged from 15 nm to 571 nm. Contact damage was simulated by means of spherical nanoindentation, and fracture was subsequently assessed by focused ion beam microscopy. It was found that, in the absence of sub-surface damage in the substrate, fracture occurs in the coating in the form of radial, and ring/cone cracks during loading, and lateral cracks during unloading. Increasing the surface roughness results in a decrease in the critical load for crack initiation during loading, and in the suppression of fracture modes during unloading from high loads. When sub-surface damage (lateral cracks) is present in the substrate, severe spalling takes place during loading, causing a large discontinuity in the load-displacement curve. The results have implications concerning the design of damage-tolerant coated systems consisting of a brittle film on a brittle substrate. |
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Keywords: | Thin films Nanoindentation Fracture Focused ion beam Surface roughness |
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