DLC thin film behaviour during multiple-cycle repeating nano-indentation

The aim of this investigation was to understand the localised failure behaviour of diamond like carbon (DLC) thin film during multiple-cycle repeating nanoindentation. The film investigated was 100 nm and 500 nm thick sputtered coated on two Si (100) wafers of 500 m thickness. Multiple-cycle repeating nano-indentation tests under diamond Berkovich and conical indenters were performed using a calibrated NanoTestTM at different load ranges between 0.1 mN and 200 mN. Each multiple-cycle nano-indentation test was conducted for a total of 20 cycles with the same load in each cycle at the same location. The shape of the indenter test probes, pre-existing residual stresses in films and indentation loads were critical in inducing the localized indentation stress leading to failure. Test results indicated forward deviation and backward deviation in force-displacement profile. An elastic finite element model during nano-indentation loading indicated that this was caused by the location of maximum stress near the interface.