Structure and mechanical properties of reactive and non-reactive sputter deposited WC based coatings

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 K-IC = 3.3 +/- 0.33 MPa center dot m(1/2) obtained by micro-mechanical testing. Furthermore, the bonding nature of carbon is distinctly affected by the reactive carbon source, leading to more pronounced pi-bonded carbon peak with increasing C2H2/Ar flow rates. (C) 2021 The Authors. Published by Elsevier B.V. CC_BY_4.0.