AVS 53rd International Symposium
    Advanced Surface Engineering Thursday Sessions
       Session SE-ThA

Paper SE-ThA4
Tailoring the Nanostructure and Surface Properties of Nanocrystalline Diamond Thin Films on Micro-End Mills for Micro-manufacturing Applications

Thursday, November 16, 2006, 3:00 pm, Room 2007

Session: Hard and Nanocomposite Coatings: Synthesis, Structure, and Properties
Presenter: A.V. Sumant, University of Wisconsin-Madison
Authors: A.V. Sumant, University of Wisconsin-Madison
P. Heaney, University of Wisconsin-Madison
F. Pfefferkorn, University of Wisconsin-Madison
R.W. Carpick, University of Wisconsin-Madison
Correspondent: Click to Email
The growing interest in high-precision machining to fabricate miniaturized parts with meso-scale machine tool systems (mMTs) for medical devices, and optical components requires high-performance micro-end mills with diameters ranging from 10 to 500 microns. This technology complements standard silicon-based microfabrication processes by its ability to directly produce true 3D structures with high accuracy, low cost, and short cycle time from metals. Presently, tungsten carbide (WC) with cobalt binder is widely used as a standard cutting tool material. However, these tools suffer from a limited operational life and have difficulty in machining adhesive metals such as aluminum and copper. Nanocrystalline diamond (NCD) thin films are an attractive possibility for coating these tools, because of its high hardness and the low friction and wear rate of its surface. We have developed a new approach using CH4/H2/Ar growth chemistry to grow a conformal, sub-micron thick coating of NCD on tungsten carbide micro-end mills using Hot Filament Chemical Vapor Deposition (HF-CVD). The percentage of Ar in the gas phase is varied to simultaneously optimize the grain size and the high sp3 content. The characterization of the sp3 content of the NCD coatings is performed using Raman and near edge x-ray absorption (NEXAFS) spectroscopy. The performance of the uncoated and NCD-coated tools have been evaluated by performing dry slot milling experiments on aluminum. The initial test results show a substantial dependence of the performance of the tool on the sp3 content of the film. Dramatic improvement in the tool integrity, extremely low wear, no observable adhesion of aluminum, and a significant reduction in the cutting forces (~ 50%) with improved surface finish are observed for NCD films with high sp3 content. This translates into a micro-machining process with minimal environmental impact, and offers great promise for micro and meso-scale manufacturing applications.