title: Why can tiAicrsiYN-based adaptive coatings deliver exceptional performance under extreme frictional conditions?
abstract: Adaptive TiAlCrSiYN-based coatings show promise under the extreme tribological conditions of dry ultra-high-speed (500-700 m min-1) machining of hardened tool steels. During high speed machining, protective sapphire and mullite-like tribo-films form on the surface of TiAlCrSiYN-based coatings resulting in beneficial heat-redistribution in the cutting zone. XRD and HRTEM data show that the tribo-films act as a thermal barrier creating a strong thermal gradient. The data are consistent with the temperature decreasing from approximately 1100-1200 degrees C at the outer surface to approximately 600 degrees C at the tribo-film/coating interface. The mechanical properties of the multilayer TiAICrSiYN/TiA1CrN coating were measured by high temperature nanoindentation. It retains relatively high hardness (21 GPa) at 600 degrees C. The nanomechanical properties of the underlying coating layer provide a stable low wear environment for the tribo-films to form and regenerate so it can sustain high temperatures under operation (600 degrees C). This combination of characteristics explains the high wear resistance of the multilayer TiAlCrSiYN/TiAICrN coating under extreme operating conditions. TiAlCrSiYN and TiAlCrN monolayer coatings have a less effective combination of adaptability and mechanical characteristics and therefore lower tool life. The microstructural reasons for different optimum hardness and plasticity between monolayer and multilayer coatings are discussed.
authors.affiliation: Micro Materials Limited, Willow House, Yale Business Village, Ellice Way, Wrexham, LL13 7YL, UK.
authors.forename: Ben D
authors.initials: BD
authors.lastname: Beake
authors.forename: German S
authors.initials: GS
authors.lastname: Fox-Rabinovich
authors.forename: Yannick
authors.initials: Y
authors.lastname: Losset
authors.forename: Kenji
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Myriam H
authors.initials: MH
authors.lastname: Agguire
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Veldhuis
authors.forename: Jose L
authors.initials: JL
authors.lastname: Endrino
authors.forename: Anatoliy I
authors.initials: AI
authors.lastname: Kovalev