Estimations of load carrying capacity in diamond-like carbon coated systems

Diamond-like carbon (DLC) coatings have shown excellent tribological properties in laboratory tests. The coatings have also been introduced to several practical applications. However, the functional reliability of the coatings 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, tool steel, cemented carbide and alumina by using two different deposition techniques: the hydrogen-free carbon coatings were deposited by a pulsed vacuum are discharge method and the hydrogenated carbon films by r.f. plasma method. The load carrying capacity of the system was evaluated by using a scratch test, Rockwell-C indentation test and ball-on-disc test. The effect of substrate material, substrate hardness, coating type and coating thickness was studied. An increase in substrate hardness increased the load carrying capacity for the coated systems as expected. The two coating types had different performance under load due to their different mechanical properties. For the load earring capacity evaluations ball-on-disc configuration is suggested.