Friction behaviour of heat isolating coatings in machining: mechanical, thermal and energy-based considerations

This paper deals with possible modifications of the frictional behaviour exhibited during the cutting process resulting from the influence of the most-commonly used heat isolating coatings deposited on a WC-Co carbide substrate. For this study, three- and four-layered coatings with intermediate Al2O3 ceramic layer and a monolayer TiAlN coating, which offer superior thermal protection of the carbide substrate, were examined. Orthogonal cutting tests were carried out by end-turning medium carbon steel and austenitic stainless steel workpieces. The experimental study was aimed at determining the fundamental frictional characteristics: dimensions of the tool-chip contact area, the friction force, the mean friction coefficient, the specific frictional energy and the corresponding thermal effects: the contact temperature and the frictional heat flux. Subsequently, results obtained for the mechanical, energy-based and thermal approaches to the frictional behaviour occurring in the carbide/ceramic coating-steel tribo-pairs were verified experimentally and the results obtained are discussed in detail. (C) 2002 Elsevier Science Ltd. All rights reserved.