Improvement of adhesion of diamond film by forming Cr nitride interlayer

There is a growing necessity for materials to be used under extreme conditions. Diamond is well known as an excellent material which has high hardness, good thermal conductivity and chemical resistance. In this study, we tried to form diamond film on iron based substrates. Direct deposition of diamond on ferrous materials suffers from adhesion problems due to the build up of a graphite layer at the interface. A successful solution to this problem was attained through the use of an intermediate layer consisting of nitrided chromium film. The Cr or Cr compound film as interlayer was deposited by DC magnetron sputtering methods. Then, additional gas nitriding was performed. Before coating, substrates were etched with Ar gas plasma which controlled the roughness of the substrate. As a result, we formed a homogeneous diamond film by using an interlayer. Diamond film was coated by hot filament CVD. Adhesion of diamond films was investigated by the scratch adhesion test. The critical load of diamond film on the Cr interlayer deposited by sputtering was very low but diamond film on CrN, Cr₂N layer formed by gas nitriding was over 80 N