Load-carrying capacity evaluation of coating/substrate systems for hydrogen-free and hydrogenated diamond-like carbon films

Diamond-like carbon (DLC) coatings have shown excellent tribological proper ties in laboratory tests. The coatings have also been introduced to several practical applications. However, the functional reliability of the coating s is often weakened by adhesion and load-carrying capacity related problems . In this study the load-carrying capacity of the coating/substrate system has been evaluated. The DLC coatings were deposited on stainless steel, alu mina and cemented carbide with two different deposition techniques: the tet rahedral amorphous carbon (ta-C) coatings were deposited by a pulsed vacuum arc discharge deposition method and the hydrogenated carbon (a-C:H) films by radio frequency (r.f.) plasma deposition method. The load-carrying capac ity of the coated systems was evaluated using a scratch test, Rockwell C-in dentation test and ball-on-disc test. The effect of substrate material, sub strate hardness, coating type and coating thickness was studied. An increas e in substrate hardness increased the load-carrying capacity for the coated systems, as expected. The two coating types exhibited different performanc e under load due to their different physical and mechanical properties. For the load-carrying capacity evaluations the ball-on-disc configuration was found to be most suitable.