Crack formation mechanisms during micro and macro indentation of diamond-like carbon coatings on elastic-plastic substrates

In the present study crack formation is investigated on both micro and macro scale using spherical indenter tips. in particular, systems consisting of elastic coatings that are well adhered to elastic-plastic substrates are studied. Depth sensing indentation is used on the micro scale and Rockwell indentation on the macro scale. The predominant driving force for coating failure and crack formation during indentation is plastic deformation of the underlying substrate. The aim is to relate the mechanisms creating both delamination and cohesive cracking on both scales with fracture mechanical models in order to quantitatively determine coating fracture properties. A non-linear elastic-plastic finite element model of the coating system which is loaded with a spherical indenter is used to simulated stress and displacement distributions in the material. The simulations are used to predict the onset of cracking and the fracture mechanisms taking place. In the study various diamond-like carbon (DLC) coatings deposited onto stainless steel and tool steel were investigated. Results primarily for one DLC system will be presented here. (C) 1998 Published by Elsevier Science S.A. All rights reserved.