The failure mechanism of diamond like coatings prepared by the filtered cathodic arc technique for minting application

The failure mechanisms of diamond like carbon (DLC) coatings prepared by filtered cathodic arc deposition technique for proof mint applications are investigated in the present study. The lifetime of the proof minting dies coated with DLC coatings is extended ∼ 8 and 4 times compared to that of un-coated and Cr-plated dies, respectively. The DLC coatings maintain a high degree of surface smoothness after coining process. The surface roughness of DLC did not show noticeable effect on the failure mechanisms of the DLC coating. The failure mechanisms of DLC coating for coining process are (1) plastic deformation of substrates that results in die sinking and/or die settling (necking expansion), (2) microcracks and local DLC coating breakdown due to the surface pin hole of DIN 2550 substrate that decrease the adhesion strength, and (3) inclusions on the blank that result in high-stress abrasion and/or impact wear.