One of the major steps in diamond deposition on tungsten carbide cutting tools by the CVD method is nucleation of diamond precursors on the substrate surface. Application of substrate biasing is one of the promising techniques for the enhancement of nucleation in HFCVD diamond coating. The objective of the present work is to study the effect of negative bias voltage to the substrate on the morphology and adhesion of the diamond coating to the substrate and to test the performance of the coated tool in machining. The beneficial effect of negative substrate bias at definite system pressure range towards achieving favourable coating having high nucleation density and good uniformity, ultimately leading to better machining performance has been confirmed. Crown Copyright (C) 2008 Published by Elsevier B. V. All rights reserved.