Numerical study of the influence of substrate material on deformation and fracture of the coating–substrate system

The experimental techniques such as instrumented indentation and scratch-test are generally used to study mechanical properties of the "coating–substrate" systems. However, technical limitations of a modern equipment cause certain difficulties in the investigation of the systems under consideration. In this paper, the processes of indentation and scratch-testing of the hardened coatings on the various substrates have been studied numerically using the movable cellular automata. The convergence analysis for elastic modulus and yield stress has been carried out to determine the representative volume element. Numerical simulation included explicitly the transition layer and the coating of 200 and 1800 nm in thickness, respectively. The elastic modulus and hardness of the system have been performed as functions of indentation depth after analyzing the simulation results using the method of Oliver and Pharr. It has been found that the substrate has a significant impact on the obtained mechanical characteristics even at the depth of indentation less than 1/10 of the coating thickness. As a result, the modeling of the scratch testing of the coating-substrate system made possible to obtain the scratch images and the time dependences of friction coefficient. Analysis of the results showed that the coating delamination occurred both in the case of oxide substrate and in the case of harder substrate; less strength is required for the latter. Delamination does not occur during the scratching of the hardened coating of titanium substrate. The value of the friction coefficient between the coating material and indenter during the instrumented scratching depends on the substrate material and it is equal to 0.25, 0.28, and 0.22 for nanostructured titanium, sapphire, and fused silica, respectively.