Nanoindentation and nanoscratch behaviors of DLC coatings on different steel substrates

Nanoindentation and nanoscratch tests were performed for diamond-like carbon (DLC) coatings on the different steel substrates in order to investigate the deformation and failure behaviors of the coating/substrate systems and their tribological properties. In this work, DLC coatings with a thickness of approximate 500 nm were grown on 9Cr18 and 40CrNiMo steel substrates by vacuum magnetic-filtering arc plasma deposition, respectively. The nanoindentation results show that the indentation response was plasticity-dominated. The peak load on sample, residual indentation depth, hardness, modulus can provide important information of the mechanical resistance of the materials tested. The scratch process with the ramping normal load was analyzed into the three regimes, which are fully elastic recovery, plastic deformation and delamination of coatings. This shows that the scratch response was controlled by plastic deformation in the substrate. The substrate plays an important role in determining the mechanical properties and wear resistance of such coatings. As a consequence, 9Cr18 steel is a better candidate of substrate materials for DLC coatings due to the better load-carrying capacity and scratch/wear resistance of DLC/9Cr18.