Optimisation of mechanical properties of plasma deposited graded multilayer diamond-like carbon coatings

Multilayer amorphous diamond-like carbon films with graded silicon and oxygen content exhibiting hardness in the range from 16 to 24 GPa were deposited using low pressure PECVD. The films were optimised for deposition on steel substrates. To evaluate the impact resistance of graded amorphous carbon films in dynamic loading wear applications an impact test has been used. During testing the specimen was cyclically loaded by tungsten carbide ball that impacts against the coating surface. Results of these tests show usability of coatings in dynamic load and enable to optimize the design of the coating/substrate system for the particular use. The films with optimum structure exhibited very good resistance against delamination, high fracture toughness and low friction coefficient. The principal new finding concerns the fracture toughness of the film and the interfacial adhesion. Upon impact test the films remain attached to the substrate, even the impact load exceeding 200 N. The films can sustain compression strains without debonding or spalling.