Cubic Boron Nitride (cBN) based nanocomposite coatings on cutting inserts with chip breakers for hard turning applications

Deposition of cBN (5∼20 μm) is of great technological importance but poses significant difficulty in terms of depositing it from vapor phase(s). Initial proof-of-concept work has indicated that a thick cBN–TiN composite coating can be deposited in a practical hybrid deposition process using electrostatic spray coating (ESC) and chemical vapor infiltration (CVI), and that coated inserts can provide significant improvement in machining performance. In this paper, the development of a nanocomposite cBN–TiN coating especially for hard turning is presented. Aspects of the coating on chip-breaker inserts, repeatability, and process optimization for the given application are discussed. Characterization of the coating shows a repeatable uniform deposition. Encouraging tool life and workpiece surface roughness have been achieved in machining of AISI 4340 hardened steels (50∼53 HRC) using the coated inserts.