An investigation of thin-film coating/substrate systems by nanoindentation

The indentation load-displacement behavior of three material systems tested with a Berkovich indenter has been examined. The materials studied were the substrate materials-silicon and polycarbonate, and the coating/substrate systems--diamond-like carbon (DLC) coating on silicon, and DLC coating on polycarbonate. They represent three material systems, namely, bulk, soft-coating/hard-substrate, and hard-coating on soft-substrate. Delaminations in the soft-coating/hard-substrate (DLC/Si) system and cracking in the hard-coating/soft-substrate system (DLC/Polycarbonate) were observed. Parallel to the experimental work, an elastic analytical effort has been made to examine the influence of the film thickness and the properties of the coating/substrate systems. Comparisons between the experimental data and analytical solutions of the load-displacement curves during unloading show good agreement. The analytical solution also suggests that the Young's modulus and hardness of the thin film can not be measured accurately using Sneddon's solution for bulk materials when the thickness of the film is comparable to the loading contact radius of the indenter. The elastic stress field analysis provides a basis for understanding the experimentally observed delaminations and cracking of the coating/substrate systems.