Journal of Materials Processing Technology 157–158 (2004) 427–433 Diffusion across PVD coated cermet tool/workpiece interface M. Sokovi´ c a,∗ , L. Kosec b , L.A. Dobrza ´ nski c a Faculty of Mechanical Engineering, University of Ljubljana, Aˇ skerˇ ceva 6, SI-1000 Ljubljana, Slovenia b Department of Materials and Metallurgy, University of Ljubljana, Aˇ skerˇ ceva 12, SI-1000 Ljubljana, Slovenia c Faculty of Mechanical Engineering, The Silesian University of Technology, Konarskiego 18a, 44-100 Gliwice, Poland Abstract According to the limitations in improving the mechanical properties of cermet cutting tools, further possibilities seem to exist to improve tool performance on the basis of reducing thermo-chemical wear, which is a result of diffusion process. This is possible by choosing a favourable combination between the substratum and PVD coating in which the process of diffusion wear is slowed down as much as possible or is not detrimental for the mechanical properties of the substratum — the basic material of the tool. In this work the diffusion across the coated cermet tools/workpiece interface has been studied. Recently, the diffusion couple method was used to study the thermochemical wear of Ti(C, N)-based cermets coated with TiN (PVD) and TiZrN (PVD) coatings as a diffusion barrier. The result of the diffusion process of the element from the tool and the workpiece through the interface is a change in the composition of the boundary layers of the tool, which increases the possibility of mechanical damage of the cutting edge. In the case of cutting with coated tools, these phenomena occur after a longer time of service in comparison to uncoated ones. © 2004 Elsevier B.V. All rights reserved. Keywords: Diffusion process; PVD coated cermet; Diffusion couple; Tool/workpiece interface 1. Introduction New trends in hard metal development also include cer- mets as cutting materials, which have been the subject of many discussions in recent years, in publications and at con- ferences [1–4]. Despite the high wears resistance of cermets and their low adhesive tendency, coatings also offer advan- tages to these cutting materials. The majority of publications in the field of wear of cermets [5–8], deals with thermo- mechanical wear while the thermo-chemical processes on the contact between the tool and workpiece have been less thoroughly researched. There is especially not enough data about the wear mechanisms of coated cermet tools [17]. In every tribocontact in cutting of materials, the TiN (PVD) coating is a protective layer against the very high tem- peratures and contact stresses [9,10]. Cutting temperatures above 700 ◦ C are typical in machining with HSS tools, while temperatures above 1000 ◦ C are typical in the high speed ∗ Corresponding author. E-mail address: mirko.sokovic@fs.uni-lj.si (M. Sokovi´ c). and heavy duty machining of steels and alloys with CVD or PVD coated carbides or cermets. At these high contact tem- peratures, chemical dissolution of the tool material into the chip on an atomic scale is accompanied by a rapid decrease in microhardness, corrosion resistance; wear resistance and strength of the tool. Extensive tests have been carried out in order to determine the performance capabilities and operating limits of cermet cutting materials [11–13]. Today, high-quality cermets are competing with uncoated and coated carbides in the field of steel machining. Despite the high wear resistance of cermets and their low adhesive tendency, coatings also offer advan- tages to these cutting materials. Low-temperature processes, such as PVD and PCVD, are employed preferably for coating cermets [1]. However, the hard CVD coating does not act as a (complete) barrier for diffusion, since diffusion processes have been traced also on the contact between the coated tool and workpiece [11]. Considering the column-like structure of the layer in PVD coatings, it is possible to expect that this kind of coating will act as a better barrier to diffusion than the CVD coating, for which a fine crystalline structure is typical [12]. 0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2004.09.067