Effect of Surface Treatments on the Structural and Mechanical Properties of Nanostructured Diamond Coatings on Tungsten
- PDF / 205,977 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 15 Downloads / 265 Views
Q8.22.1
Effect of Surface Treatments on the Structural and Mechanical Properties of Nanostructured Diamond Coatings on Tungsten Carbide Cutting Tools Vaibhav Vohra, Shane A. Catledge, and Yogesh K. Vohra Department of Physics, University of Alabama at Birmingham (UAB) Birmingham, AL 35294-1170, U.S.A. ABSTRACT Chemical Vapor Deposition (CVD) using hydrogen, methane, and nitrogen feed gases has proven to be useful in depositing well-adhered diamond films on metal substrates. These films have already found a market in the cutting tool industry as coatings on cobalt-cemented tungsten carbide (WC-Co) inserts. The purpose of this investigation is to examine how the thermal and chemical pre-treatments typically used for carbide inserts (to remove the cobalt binder near the surface) affect the structure and interfacial adhesion of the diamond coating. Removal of the cobalt binder phase in various pre-treatment methods has been shown to minimize its catalytic effect of graphite formation during diamond deposition by CVD. The diamond-coated inserts in our study were characterized using x-ray diffraction, Raman spectroscopy, atomic force microscopy, and Rockwell indentation testing. We use an unconventionally high methane concentration in the feedgas in order to saturate the growth surface with carbon, thereby limiting cobalt migration from the bulk to the surface and reducing the dissolution and diffusion of carbon atoms coming from the plasma. Nitrogen is used in the feedgas in order to provide a tough, single-layer nanocrystalline diamond film structure. In addition, a multi-layer (nano-/micro-/nano-crystalline) CVD diamond film was grown by controlling the flow of nitrogen in order to show its characteristics in comparison with the single layer nanocrystalline diamond film. The multilayer film on the thermally-treated insert shows enhanced interfacial adhesion and fracture toughness when compared to other pretreatments and diamond coatings. This was demonstrated by indentation tests using 1470 N load. INTRODUCTION Because of their extreme hardness, high thermal conductivity, chemical inertness and other excellent intrinsic properties [1], diamond films produced by various vapor deposition techniques have generated intense interest in several scientific and industrial fields. The diamond market for the cutting tool industry has been based primarily on the use of conventional singlecrystal and sintered polycrystalline diamond (PCD) tools. Diamond cutting tools offer 100 times the life per price advantage over WC-Co and standard TiN or TiB2 coatings for the machining of aluminum-silicon alloys. Other non-ferrous materials, including metals (aluminum, copper, their alloys, etc.) and non-metals (fiber-reinforced plastics, carbon, ceramics, wood, etc.) are excellent candidates for diamond tools. The automotive market is especially attractive for diamond tools since they are the only competitors in the aluminum drive-train market. These products, however, are expensive and their shapes and dimensions are restricted by nature of
Data Loading...
