Nano-scratching process and fracture mechanism of amorphous carbon films

The nano-scratch behavior of amorphous carbon films prepared on Ti alloy substrate by rf PECVD was evaluated using a nano indenter system with an attachment for lateral force measurement. The scratching processes were analyzed to understand the deformation behavior and the failure mechanism of the films. It was concluded that, three processes containing fully elastic recovery, asynchronous recovery, and delaminating of the film, successively occurred with the increase of load during scratching; in the first regime, no damage could be found on the surface of the film, in the second regime, due to asynchronous recovery of the film and the substrate, a trace like fish bone was formed, which was composed of tiny cracks along the track of the indenter. It was only in the third regime that the critical load was reached and partial spalliation of the film was detected with careful examination. It was determined that the film spalliation originated right from the fish bone cracking, and the fish bone was just a profiling of the Berkovich indenter. By our model, the film was delaminated from the substrate due to combining effect of parallel cracks and the separation of the interface between the film and the substrate.