FATIGUE FAILURE MECHANISMS OF MULTILAYER AND MONOLAYER PHYSICALLY VAPOR-DEPOSITED COATINGS IN INTERRUPTED CUTTING PROCESSES

The fatigue failure mechanisms of PVD coatings in interrupted cutting processes are comprehensively detected in this paper. The fatigue and the wear behaviour of single and multilayer coatings on high speed ste el and on cemented carbides substrates are investigated experimentally in milling and analytically through a finite elements method simulati on of the cutting process. The initiation and progress of the tool fai lure is depicted through scanning electron microscopy (SEM) and energy -dispersive X-ray microspectral investigations of the used cutting edg es. Furthermore, the FEM simulation of the contact between the tool an d the workpiece enables a quantitative description of the influence of mechanical stress components on the coating failure. Hereby, existing critical coating fatigue stresses and experimentally derived technolo gical cutting data were considered. The experimental and computational results exhibit quantitatively the effect of tool design on the overa ll cutting performance as well as the influence of the coating fatigue behaviour for various substrates and film structures. (C) 1998 Elsevi er Science S.A. All rights reserved.