Industrial scale deposition of well adherent superhard and low friction C-DLC coatings grown by HIPIMS and anode assisted unbalanced magnetron sputtering

The paper describes a PVD coating method to produce advanced C-DLC coatings with either superhard or softer low friction properties. This is achieved by deposition of metal-free carbon coatings from an industrial batch type coater equipped with 5 unbalanced magnetrons (UBM). Four cathodes carrying pure graphite targets form in combination with amplifying electromagnetic coils a magnetically closed loop arrangement. The fifth cathode is operated as HIPIMS cathode. The C-DLC coatings are grown in a reactive Ar + C2H2 atmosphere. Structure-less metal-free coatings with universal hardness values between HU 40 and 55 GPa and low friction values of 0.05 to 0.07 (unlubricated sliding friction against steel) were deposited onto threefold rotated stainless steel substrates. These results have been attained by using a central anode providing a non-interrupted uniform moderate low energy ion bombardment (75 eV) during the complete phase of UBM film growth. Prior to the pure C-DLC film deposition a WC based interface is produced. This process is initiated by operating the HIPIMS cathode generating a plasma containing multi-ionized W atoms. Under the influence of a high negative substrate bias W is implanted into the growing carbon film. Reducing the bias voltage a dense WC base layer is formed which contributes further to excellent adhesion. Two major types of films may be produced in one and the same chamber without target change, superhard and softer very low friction coatings namely. Deposition parameters were optimized to achieve substrate temperatures <= 200 degrees C. The process is characterized by a minimum of necessary process control.