Hardness of and stress in tungsten carbide-diamond like carbon multilayer coatings

Hardness of and stress in tungsten carbide-diamond like carbon (WC-DLC) multilayer coatings sputtered in reactive argon/acetylene plasma have been studied as a function of the bilayer thickness. The multilayer structure has been deposited by a periodic modulation of the reactive acetylene gas flow from 0 to 5 sccm, producing a series of pure WC layer and W-C:H amorphous layer. Internal stress and microstructure have been investigated by wafer curvature and transmission electron microscopy whereas hardness was obtained by nanoindentation. In a previous paper on WC-DLC multilayers [Appl. Phys. Letts. 90, 021913 (2007)] we reported an interface stress of 11.12 N/m. By changing the layout of the gas lines in the deposition equipment, a new series of multilayers were produced. Our results show that in this new series of multilayers, the compressive stress exhibits the same dependence on bilayer thickness as reported before and a huge interface stress of 8.5 N/m is still present in the multilayer. In this new series of multilayers, we are reporting a hardness of 18.7 GPa, and contrarily to the observed in the first set of WC-DLC multilayers. the hardness does not depend on the bilayer thickness. These results are discussed in terms of the microstructure of the individual layers and the structure of the interfaces. (C) 2008 Elsevier B.V. All rights reserved.