Porosity of thin diamond-like carbon films deposited by an arc discharge method

In an arc-discharge method, diamond-like carbon (DLC) films are deposited by condensation of highly ionized carbon plasma on a substrate. These films, which are virtually hydrogen free, are best characterized as amorphous diamond. As reported previously, a low friction coefficient and a wear coefficient an order of a magnitude lower that that of silicon carbide has been determined in dry sliding contact with hardened carbon steel. These films are also presumably inherently highly corrosion resistant. However, utilization of DLC films in corrosive evironments depends on the degree of porosity. In this work we have determined the porosity of films deposited either with or without enhanced particle filtering, which was accomplished by hindrance plates inside the curved-magnetic-field solenoid. As substrates, discs of plain carbon steel with a diameter of 100 mm were employed. The samples were exposed to a neutral salt spray and the pores were determined using a Ferroxyl test and electrochemical measurements. The microstructural features and defects identified in corrosion and porosity tests were studied in detail using metallographic methods and scanning electron microscopy. On the basis of the results, the possibilities for using DLC films in corrosive environments are discussed.