Properties of ta-C Films for Tools and Machinery Parts

The pulsed vacuum arc discharge is an effective technology for the deposition of ta-C coatings on tools and machinery parts. The properties of these carbon coatings differ substantially from conventional hard nitride films particularly with regard to hardness and wear-resistance. The paper shows analytical results of ta-C films in comparison to such hard coatings. Thereby different methods are applied for determination of adhesion, friction, wear-resistance, and indentation hardness. A simple correlation was found between indentation hardness and wear-resistance over a wide range of hard materials. Furthermore, all investigated films have a strong adhesion on steel in conventional Rockwell tests. But in scratch tests with increasing normal forces brittle ta-C films delaminate at lower forces from the surface compared to nitride coatings.