Evaluation of Adhesions of DLC/CrN Multi-layered Coatings on Stainless Steel

Adhesion of DLC/CrN multilayered coatings onto stainless steel was evaluated using three adhesion tests: the scratch test, HRC indentation test, and microindentation test. In the DLC/10 μmt-CrN/SUS304 sample, the critical load (Lc) by scratch test improved to 28 N. In a SUS304 substrate reinforced by sulphonitriding, it improved to 52 N.The HRC indentation test revealed cracks and delamination of the DLC coating around the indentation hole. The force-depth (P−h) curves in the microindentation test showed a few discontinuous behaviors (pop-in) accompanying DLC delaminations. Cross-sectional images under the dent were obtained using FIB observation, showing that pop-ins occurred at the interface between DLC and the Cr-C gradient layer. In the DLC/2 μmt-CrN/SUS304 sample, no delamination of DLC was observed in the microindentation test, although DLC varied with plastic deformations of SUS304 substrate in the microindentation test, and DLC delaminations were observed at the DLC − Cr-C interface.