Evaluation of failure properties of a DLC/steel system using combined nanoindentation and finite element approach

Abstract In the current work, the failure properties of a DLC/steel system are quantitatively characterized by nanoindentation using a conical indenter. The DLC coating with thickness of ~1.7 μm is obtained by physical vapor deposition on a 20CrMnMo gear steel substrate. During the nanoindentation, it is noticed that the circumferential cracking and delamination occur in the coating and interface, respectively. In terms of the energy release theory, the coating fracture toughness and interfacial bonding energy are calculated from the steps in the loading curves. The results show that the interfacial adhesion energy and the fracture toughness are individually 2 and ~1.579 MPa·m 1/2 for the DLC coating on steel substrate, which accords well with the published data. Furthermore, based on the mechanical properties and cohesive energies of materials obtained above, finite element simulations under the ideal situation (defect-free and residual stress-free) including cohesive zone model are carried out to acquire coating fracture and interfacial bonding strengths as well as evolutions of failures in the coating-substrate system. The present model may find useful application not only for DLC but also for other coatings.