Proposed Wear Mechanism for Titanium Nitride Coated High Speed Steel

Abstract

An extensive study has been carried out to investigate the wear of a range of high speed steel tools coated with an ion plated titanium nitride layer used at a variety of cutting speeds and feed rates when machining cast iron and an AISI/SAE 4140 steel. Examination of the form of flank wear v. cutting time curves indicated that a stable micro built-up edge is produced rapidly on the coated tools which causes reduced primary wear and, hence, increased tool life. The production of the stable micro built-up edge is shown to be a result of a major change in the contact conditions between the chip and the tool for the coated tool which is a consequence of a reduced friction force on the tool face. Supplementary experiments including quick stop tests, cutting force measurements, contact length and chip thickness measurements, and high magnification scanning electron microscopy have confirmed the validity of the proposed mechanism of reduced primary wear for coated tools.