Structure and mechanical properties of reactive and non-reactive sputter deposited WC based coatings
T. Glechner, Rainer Hahn, L. Zauner, S. Rißlegger, A. Kirnbauer, P. Polcik, H. Riedl
Abstract
During the growth of WC based thin films, carbon can be introduced by either a non-reactive or reactive deposition route. In this study, we compare the influence of the carbon origin on the coating properties, sputtering three different target materials – a ceramic WC, a ceramic WC including a conventional cobalt binder, and a metallic tungsten (W) target – in reactive (acetylene, C2H2) as well as non-reactive (pure Ar) atmospheres. The morphology changes, independently to the target type and atmosphere used, from crystalline (hex-W2C rich to pure fcc-WCx) to a nanocomposite (fcc-WCx nanometre sized grains embedded in an amorphous matrix) structure, up to amorphous coatings, only dominated by the prevalent C/W ratio. The cobalt binder however leads to a preferred amorphization of the coatings. The highest hardness is obtained for predominantly fcc structured WC0.67 (WC ceramic target), H = 40 ± 1.7 GPa, exhibiting also an excellent intrinsic fracture toughness of KIC = 3.3 ± 0.33 MPa·m1/2 obtained by micro-mechanical testing. Furthermore, the bonding nature of carbon is distinctly affected by the reactive carbon source, leading to more pronounced π-bonded carbon peak with increasing C2H2/Ar flow rates.