Investigation of structure and mechanical properties of magnetron sputtered monolayer and multilayer coatings in the ternary system Si-B-C

In the present work SiC and B4C monolayers as well as SiC/B4C multilayer coatings have been investigated with respect to their composition and mechanical properties. The coatings have been deposited on silicon substrates and polished cemented carbide inserts by non-reactive dual radio frequency (r.f.) magnetron sputtering from stoichiometric, high-purity silicon carbide (99.5%) and boron carbide (99.9%) targets. Amorphous stoichiometric SiC and B4C have been achieved with high hardness of 2950 HV0.01 and 4160 HV0.01 with a residual stress of -3.4 GPa and -2.9 GPa, respectively. The number of monolayers in the multilayer system with a constant total layer thickness has been varied in order to investigate the influence of the number of interfaces on film composition and properties. Additionally, the monolayer thickness ratio for a constant modulation period (double layer thickness) was varied. In this multilayer system no notable hardness enhancement could be observed. Despite the absence of the hardness enhancement, the toughness is expected to be enhanced due to stress relaxation and a reduction of crack propagation by crack dissipation along the interfaces. An abrupt interface is considered to be an indispensable requirement. However, the strain fields and the difference of the mechanical properties in the interfacial region are also of importance. (C) 2006 Elsevier B.V. All rights reserved.