Hardmetal woodcutting tool tips coated with tetrahedral amorphous carbon

Woodcutting tools with hardmetal (WC-Co) tool tips were coated with a high-quality (80% sp(3) bonding fraction) tetrahedral amorphous carbon (ta-C) him. The coatings were produced by filtered cathodic vacuum-are (FCVA) deposition. The problem with poor adhesion between the ta-C film and cobalt was solved by using an intermediate chromium layer structure. The adhesion was tested with a conventional scratch tester. In the case of a 1.2 mu m thick ta-C film with intermediate layer structure the critical load value was 31.6 N; without the intermediate layer it was 16.2 N. The lifetime of the ta-C-coated woodcutting tool was tested under normal production conditions with a computer numerical control (CNC) woodcutting machine. The lifetime of the woodcutting tool tip improved by a factor of three in the case of a 2.1 mu m thick multilayer (ta-C/Cr) film coating and by a factor of 1.5 in the case of a 1.0 mu m thick ta-C film coating with an 0.5 mu m thick intermediate chromium layer. (C) 1999 Elsevier Science S.A. All rights reserved.