Abstract
Two bilayer systems (TaN/Mo and ZrN/Mo) have been deposited onto WC–Co cermets in order to limit the cobalt diffusion from this substrate and to promote the diamond nucleation. Mo was the top layer. The diamond CVD coating process includes two steps: 1) Bias Enhance Nucleation (BEN) step for diamond nucleation control, 2) diamond growth step with a time-modulated negative substrate polarization to form nanocrystalline diamond grains (NCD). Original cluster morphology of diamond film was obtained, and patented under the name PyrNCD (for pyramidal NCD). Clusters are multilayered and composed of two diamond layers (resp. grain sizes: about 1nm and 10nm) periodically repeated. Thermomechanical computations have been carried out to understand the stress distribution inside the multilayer systems before and after diamond deposition. Computation results demonstrate that the architecture of the system is optimized and the morphology of PyrNCD diamond clusters should not degrade their substrate adhesion. A mechanism for the formation of the diamond layer is proposed for a time-modulated polarized diamond growth process to understand the formation of both the specific morphology and the NCD grains.
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