The nano-scratch behaviour of different diamond-like carbon film-substrate systems

The nano-scratch behaviour of diamond-like carbon films on a Ti alloy and Si substrate was evaluated. For both samples, three processes - fully elastic recovery, plastic deformation, and delamination and pulling-off of the films, occur successively with increasing load during scratching. The loads (Lc _L) corresponding to the peeling-off of the films during the up-loading were 75 and 70 mN for Ti alloy and Si. However, the films on Si were delaminated during unloading, and the relevant load (Lc_U) was only 45 mN. This probably originates from the distribution status of the plastic deformation both in the films and the substrates. Therefore, the nano-scratch test can be applied not only to obtain the cracking resistance (Lc_L) characterizing the cohesion strength of films during up-loading but also to determine the delamination resistance (Lc_U) related to the adhesion strength of the film-substrate during unloading.