Influence of substrate bias on machining performance of TiAlN-coated drill bits

Abstract

ABSTRACT The present study investigates the influence of substrate bias on edge-rounding of TiAlN-coated drill bits arising out of coating deposition and the resulting cutting performance while machining Inconel 718. Tungsten carbide (WC) drill bits were deposited with TiAlN coating through a cathodic arc physical vapor deposition (CAPVD) system. Five different substrate bias voltages varying from −20 V to −60 V were employed for the deposition. The hardness, adhesion strength, and residual stress were significantly influenced by substrate bias. The sharp edges of coated drill bits exhibited significant edge-rounding at relatively higher levels of substrate bias. The reason for such edge-rounding is the re-sputtering and residual stress-induced micro-chipping of the previously formed coating layer during the deposition. The edge-rounding of drill bits was in the order of: 20 V <30 V <40 V <50 V <60 V. The drill bits deposited at −50 V substrate bias exhibited the best tool life owing to optimum edge radius (resulting in better edge stability) and coating properties. The present study helps identify an optimum level of substrate bias, which results in a favorable edge radius and the best tool life of the coated drill bits.