Diamond/Carbide Nano-Composite Gradient Films: a Route to solve the Adhesion Issues of Diamond Films

Abstract

ABSTRACTDue to their outstanding mechanical properties diamond films are ideal candidates for many cutting and machining applications. However, industrial applications of these films are limited due to poor adhesion. Two main reasons causing this poor adhesion, which are based on the extrinsic physical and chemical properties of diamond, can be identified: High mechanical stresses induced by a difference of the thermal expansion coefficient between the diamond film and the substrate as well as a catalytic effect in case of metallic substrates containing iron-, cobalt- and nickel that, in combination with a methane atmosphere during deposition, leads to soot formation. One option to overcome these difficulties is to provide an interfacial layer that acts as adhesion layer as well as barrier layer to prevent the catalytic effect of the substrate elements. Even though some successful examples exist, this approach usually requires a time consuming and expensive multi-step process.In this paper, the synthesis of nanocrystalline diamond/carbide composite films with a compositional gradient will be reported. Focusing on the example of diamond/ß-SiC the possibility to create a gradient layer ranging from ß-SiC to diamond in a controlled manner will be shown. The films are prepared by a Microwave Assisted Plasma Chemical Vapour Deposition process (MWCVD) using H2, CH4 and Tetramethylsilane (TMS) as reactive gases. The structure, grain sizes, and volume fractions of the components of these composite films, which consist of a mixture of diamond and carbide phase, can be controlled by adjusting the concentrations of the reactive gases in the gas mixture. This strategy, which handles all depositions in one process step, should allow for an improved diamond film adhesion on tools. The preparation and characterization of the composite films with special emphasize on their mechanical and tribological properties will be discussed and a short outlook on other diamond/carbide systems will be given.