title: Hierarchical adaptive nanostructured PVD coatings for extreme tribological applications: the quest for nonequilibrium states and emergent behavior.
abstract: Adaptive wear-resistant coatings produced by physical vapor deposition (PVD) are a relatively new generation of coatings which are attracting attention in the development of nanostructured materials for extreme tribological applications. An excellent example of such extreme operating conditions is high performance machining of hard-to-cut materials. The adaptive characteristics of such coatings develop fully during interaction with the severe environment. Modern adaptive coatings could be regarded as hierarchical surface-engineered nanostructural materials. They exhibit dynamic hierarchy on two major structural scales: (a) nanoscale surface layers of protective tribofilms generated during friction and (b) an underlying nano/microscaled layer. The tribofilms are responsible for some critical nanoscale effects that strongly impact the wear resistance of adaptive coatings. A new direction in nanomaterial research is discussed: compositional and microstructural optimization of the dynamically regenerating nanoscaled tribofilms on the surface of the adaptive coatings during friction. In this review we demonstrate the correlation between the microstructure, physical, chemical and micromechanical properties of hard coatings in their dynamic interaction (adaptation) with environment and the involvement of complex natural processes associated with self-organization during friction. Major physical, chemical and mechanical characteristics of the adaptive coating, which play a significant role in its operating properties, such as enhanced mass transfer, and the ability of the layer to provide dissipation and accumulation of frictional energy during operation are presented as well. Strategies for adaptive nanostructural coating design that enhance beneficial natural processes are outlined. The coatings exhibit emergent behavior during operation when their improved features work as a whole. In this way, as higher-ordered systems, they achieve multifunctionality and high wear resistance under extreme tribological conditions.
authors.affiliation: Department of Mechanical Engineering, McMaster University, 1280 Main St. W. Hamilton, Ontario L8S 4L7, Canada.
authors.forename: German S
authors.initials: GS
authors.lastname: Fox-Rabinovich
authors.affiliation: Materials Research Laboratory, Kobe Steel Ltd, 1-5-5 Takatsuda-dai, Nishi-ku, Kobe, Hyogo, 651-2271, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Yamamoto
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.affiliation: All-Russian Railway Research Institute, 10 Third Mytishchinskaya Street, Moscow, 29851, Russia.
authors.forename: Iosif S
authors.initials: IS
authors.lastname: Gershman
authors.affiliation: Surface Phenomena Research Group, CNIICHERMET, 9/23, 2-nd Baumanskaya Street, Moscow, 105005, Russia.
authors.forename: Anatoly I
authors.initials: AI
authors.lastname: Kovalev
authors.affiliation: Department of Mechanical Engineering, McMaster University, 1280 Main St. W. Hamilton, Ontario L8S 4L7, Canada.
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Veldhuis
authors.affiliation: EMPA, Solid State Chemistry and Catalysis, CH-8600 Dübendorf, Switzerland.
authors.forename: Myriam H
authors.initials: MH
authors.lastname: Aguirre
authors.affiliation: Department of Mechanical Engineering, McMaster University, 1280 Main St. W. Hamilton, Ontario L8S 4L7, Canada.
authors.forename: Goulnara
authors.initials: G
authors.lastname: Dosbaeva
authors.affiliation: Albengoa Research, Energía Solar 1, Palmas Altas, Seville, 41014, Spain.
authors.forename: Jose L
authors.initials: JL
authors.lastname: Endrino
keywords: adaptive materials; dissipative structures; emergent behavior; extreme applications; hierarchical materials; multi-functionality; nano-laminates; nano-structured PVD coatings; nano-tribology; self-organization; surface engineering; surface phenomena