Microstructure Coating Influence for Optimized Diamond Deposition

Abstract

Diamond films grown by Chemical Vapor Deposition (CVD) are widely used as surface overlay coating onto WC-Co cutting tools to develop their performances. To improve the diamond adhesion with the substrate, many pre-treatment methods have been applied such as giving a suitable diffusion barrier layer on the substrates. Single zirconium and tantalum nitride layers have been sputtered onto WC-Co substrates as diffusion barriers and buffer layers under specific reactive sputtering conditions. Microstructure of the tantalum nitride layer has been controlled using process parameters in order to understand mechanisms occurring during Co diffusion in correlation with microstructure. Moreover, a multilayer coating composed of TaN and ZrN thin film sequences as diffusion barrier is also evaluated. To improve the nuclei density of diamond during CVD processing, a thin Mo extra layer has been added (500 nm) whatever the diffusion barrier used. In this study, bilayer and multilayer systems have been tested to optimize nanocrystalline CVD diamond deposition grown with negative biased substrates. For all systems, after diamond deposition, a massive carburization of molybdenum and tantalum nitride is observable whereas zirconium nitride is not. A TEM study is done to improve understanding of phenomena occurring at the interfaces during the process. The key role played by each layer microstructure is discussed.