Diamond-like coatings prepared by the filtered cathodic arc technique for minting application

The wear resistance of hydrogen-free amorphous diamond-like carbon (DLC) thin films prepared by filtered cathodic arc deposition technique using the carbon source are reported. Emphasis is placed on the lifetime of the proof minting dies coated with DLC coatings, which can extend approximately 8 and 4 times corresponding to that of un-coated and hard chromium plating dies. The film thickness of DLC coatings are controlled to approximately 0.6 μm in order to maintain a high degree of surface smoothness of the proof minting dies. The adhesion critical load value as evaluated by the scratch test associated with the failure mechanism was observed to be more than 30 N. The sp3 bond fraction in DLC films as examined by Raman spectroscopy and X-ray photoelectron spectroscopy was approximately 72%. The micro-hardness of the DLC film is approximately 3540 Hv. The process of the filtered cathodic arc deposited DLC coating offers an alternative of hard chromium plating and extended die lifetimes compared to conventional die surface treatments.