AN INVESTIGATION OF THIN-FILM COATING SUBSTRATE SYSTEMS BY NANOINDENTATION/

The indentation load-displacement behavior of three material systems t ested with a Berkovich indenter has been examined. The materials studi ed were the substrate materials-silicon and polycarbonate, and the coa ting/substrate systems--diamond-like carbon (DLC) coating on silicon, and DLC coating on polycarbonate. They represent three material system s, 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/Pol ycarbonate) were observed. Parallel to the experimental work, an elast ic analytical effort has been made to examine the influence of the fil m thickness and the properties of the coating/substrate systems. Compa risons between the experimental data and analytical solutions of the l oad-displacement curves during unloading show good agreement. The anal ytical 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 th e loading contact radius of the indenter. The elastic stress field ana lysis provides a basis for understanding the experimentally observed d elaminations and cracking of the coating/substrate systems.