Effects of Deposition Temperature on Synthesis of Ultrananocrystalline Diamond/Amorphous Carbon Composite Films on Cemented Carbide Substrate By Coaxial Arc Plasma Deposition

Abstract

Synthesis of hard carbon coatings on cutting tools is indispensable for machining the nonferrous materials and carbon fiber composites. Diamond, an allotrope of carbon, is classified at the top of carbon coatings for its unique characteristics, it has the highest known hardness and thus provides superior wear resistance. A diamond crystal consists of carbon atoms tetrahedrally bonded with sp3 hybrid bonds. On the basis of its crystal size, polycrystalline diamond is categorized to microcrystalline, nanocrystalline, and ultrananocrystalline diamond. Ultrananocrystalline diamond/amorphous carbon composite (UNCD/a-C) films, wherein a large number of diamond grains with diameters of less than 10 nm are embedded in an amorphous carbon matrix. A high hardness of UNCD/a-C films is attributed to the refinement of grains in nanoscale and its resultant high content of sp3-bonded carbon. To provide highly energetic carbon atoms and thus sp3-rich amorphous carbon films, cathodic arc discharge has ever been employed. In addition to the merits of cathodic arc discharge, coaxial arc plasma deposition technique (CAPD) has the following distinctive feature: a coaxial arc plasma gun is equipped with an anodic cylinder that can bunch ions ejected from a cathodic graphite rod located inside the cylinder. Owing to this structure, a supersaturated condition with highly energetic ions can be realized, which is desired for the growth of UNCD crystallites In this work, the influences of deposition temperature on growth and mechanical properties of the UNCD/a-C films were studied. The films were deposited at different temperatures on cemented carbide (WC-6wt.% Co) plate substrates by using CAPD. The hardness and elastic modulus were investigated by nanoindentation. Structural characterizations of the films have been examined by X-ray diffraction, scanning electron microscopy, hard X-ray photoelectron spectroscopy, and energy-dispersive X-ray. The revealed mechanical and structural properties will be presented.