Wear of TiC-coated carbide tools in dry turning

This paper examines the flank and crater wear characteristics of titanium c arbide (TiC)-coated cemented carbide tool inserts during dry turning of ste el workpieces. A brief review of tool wear mechanisms is presented together with new evidence showing that wear of the TiC layer on both flank and rak e faces is dominated by discrete plastic deformation, which causes the coat ing to be worn through to the underlying carbide substrate when machining a t high cutting speeds and feed rates. Wear also occurs as a result of abras ion, as well as cracking and attrition, with the latter leading to the wear ing through of the coating on the rake face under low speed conditions. Whe n moderate speeds and feeds are used, the coating remains intact throughout the duration of testing. Wear mechanism maps linking the observed wear mec hanisms to machining conditions are presented for the first time. These map s demonstrate clearly that transitions from one dominant wear mechanism to another may be related to variations in measured tool wear rates. Compariso ns of the present wear maps with similar maps for uncoated carbide tools sh ow that TiC coatings dramatically expand the range of machining conditions under which acceptable rates of tool wear might be experienced. However, th e extent of improvement brought about by the coatings depends strongly on t he cutting conditions, with the greatest benefits being seen at higher cutt ing speeds and feed rates. (C) 1999 Elsevier Science S.A. All rights reserv ed.