Investigation of electronic and atomic structure of tribofilms on the surface of cutting tools with TiAlCrSiYN and multilayer TiAlCrSiYN/TiAlCrN coatings during machining of hardened steels

Abstract

AbstractNanostructured single‐layer TiAlCrSiYN and multilayer TiAlCrSiYN/TiAlCrN coatings were deposited by a hybrid physical vapor deposition (PVD) coater with a plasma‐enhanced type arc source. Yttrium was added as a surfactant element to stabilize the nanostructure of the coating. The paper reports on the X‐ray photoelectron spectroscopy(XPS) and analysis of the extended energy loss fine structure(EELFS) spectroscopy studies of the electronic and atomic structure of tribofilms formed on the surface of cutting tools during high‐speed machining of hardened tool steels. It was shown by electron spectroscopy investigations that two types of tribofilms form on the surface of cutting tools. The first type is sapphire‐like (AlO) and mullite‐like (AlSiO) films with high protective ability. The second type has an amorphous‐like structure and a high density of dangling bonds enhancing their lubrication properties at elevated temperatures. This unique combination of thermal‐barrier and frictional characteristics of these tribofilms allows the cutting tool to stand high‐speed cutting conditions and achieve reliable tool life. A more intensive generation of mullite‐like tribofilms was observed in the single‐layer coating in contrast to the multilayer one, where generation of the sapphire‐like component prevailed. Most probably, the nanostructuring of the coating increases the interface and grain boundary diffusion and activates the formation of a high‐temperature tribo‐oxide. Copyright © 2010 John Wiley & Sons, Ltd.