G.S. Fox-Rabinovich

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.

Nanocrystalline coating design for extreme applications based on the concept of complex adaptive behavior

The development of effective hard coatings for high performance dry machining, which is associated with high stress/temperatures during friction, is a major challenge. Newly developed synergistically alloyed nanocrystalline adaptive Ti0.2Al0.55Cr0.2Si0.03Y0.02N plasma vapor deposited hard coatings exhibit excellent tool life under conditions of high performance dry machining of hardened steel, especially under severe and extreme cutting conditions. The coating is capable of sustaining cutting speeds as high as 600 m/min. Comprehensive investigation of the microstructure and properties of the coating was performed. The structure of the coating before and after service has been characterized by high resolution transmission electron microscopy. Micromechanical characteristics of the coating have been investigated at elevated temperatures. Oxidation resistance of the coating has been studied by using thermogravimetry within a temperature range of 25–1100 °C in air. The coefficient of friction of the coatings ...

Features of self-organization in ion modified nanocrystalline plasma vapor deposited AlTiN coatings under severe tribological conditions

Features of self-organization in the hard AlTiN plasma vapor deposited (PVD) coatings have been investigated under severe frictional conditions associated with high temperatures and stresses, which are typical for high-speed cutting. Aluminum-rich (around 67at.%) (Al67Ti33)N hard PVD coating has been modified by means of the “duplex” post-treatment, including annealing in vacuum at 700°C with subsequent ion implantation by Ar+. Structure modification of the surface layer has been studied using x-ray photoelectron spectroscopy, electron energy loss fine structure, and high resolution electron energy loss spectroscopy methods. Micromechanical characteristics of the coating have been studied using the nanoindentation method. Coefficient of friction was measured in relation to temperature. Wear behavior of the coating has been investigated under severe conditions of HSC of 1040 steel. Results show that the enhancement of nonequilibrium processes during friction due to ion implantation of AlTiN coating by Ar+ ...

Mechanism of adaptability for the nano-structured TiAlCrSiYN-based hard physical vapor deposition coatings under extreme frictional conditions

Recently, a family of hard mono- and multilayer TiAlCrSiYN-based coatings have been introduced that exhibit adaptive behavior under extreme tribological conditions (in particular during dry ultrahigh speed machining of hardened tool steels). The major feature of these coatings is the formation of the tribo-films on the friction surface which possess high protective ability under operating temperatures of 1000 °C and above. These tribo-films are generated as a result of a self-organization process during friction. But the mechanism how these films affect adaptability of the hard coating is still an open question. The major mechanism proposed in this paper is associated with a strong gradient of temperatures within the layer of nano-scaled tribo-films. This trend was outlined by the performed thermodynamic analysis of friction phenomena combined with the developing of a numerical model of heat transfer within cutting zone based on the finite element method. The results of the theoretical studies show that t...

Self-Organization during Friction in Complex Surface Engineered Tribosystems

Self-organization during friction in complex surface engineered tribosystems is investigated. The probability of self-organization in these complex tribosystems is studied on the basis of the theoretical concepts of irreversible thermodynamics. It is shown that a higher number of interrelated processes within the system result in an increased probability of self-organization. The results of this thermodynamic model are confirmed by the investigation of the wear performance of a novel Ti0.2Al0.55Cr0.2Si0.03Y0.02N/Ti0.25Al0.65Cr0.1N (PVD) coating with complex nano-multilayered structure under extreme tribological conditions of dry high-speed end milling of hardened H13 tool steel.

Why can TiAlCrSiYN-based adaptive coatings deliver exceptional performance under extreme frictional conditions?

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.

Characteristic features of alloying HSS-based deformed compound powder materials with consideration for tool self-organization at cutting: 1. Characteristic features of wear in HSS-based deformed compound powder materials at cutting

Abstract Characteristic features of wear in tools made of high-speed steel (HSS) based deformed compound powder materials (DCPMs) were investigated at cutting. It was shown that HSS-based powder tool materials additionally alloyed by titanium carbides feature an abnormally high wear resistance and could be placed into a new class of self-organizing tool materials. In particular, DCPM-containing titanium carbide as a base and HSS as a binder can be classed with such materials. Self-organization of such materials is manifested in their ability to form stable high-strength phases that effectively protect the surface from external impacts at cutting. It was found using AES and SIMS methods, that during the process of cutting one can observe the transformation of carbide TiC into thin surface films in the form of titanium-oxygen compounds. This substantially enhanced frictional properties at operational temperatures and significantly increased the cutting tool wear resistance. As a result, the wear resistance of this tool is 2.0–3.5 times higher than that of usual high-speed steel tools.

Impact of ion modification of HSS surfaces on the wear resistance of cutting tools with surface engineered coatings

Abstract The paper considers some ways to improve surface engineered coatings for cutting tools. These coatings were formed by two stages: diffusion saturation with nitrogen (ion nitriding) and application of the (Ti, Cr)N hard coating by means of the cathode arc plasma deposition process (CAPDP). The coating includes also an additional ion alloyed layer applied to the previously nitrided surface of HSS. Such multilayered coating makes it possible to significantly increase (in 2.1–2.4 times) the wear resistance of a cutting tool by extending the stage of normal wear. There were studied 16 chemical elements implanted into the base surface and those of four antifrictional materials effecting on the life of a HSS cutter with a surface engineered coating. It was shown that leading positions in wear resistance are taken by coatings with a modified sublayer of elements with high antifrictional properties. A compromise between the high wear resistance and reliability of a coating, which is characterized by a high adhesion to the substrate, is observed in the multilayered coating that contains a sublayer enriched with indium. Indium is present in the sublayer both in metal and bound states (In–N). The positive effect of indium on wear resistance appears to be tied with two types of phenomena developing on the friction surface. Acting as a liquid lubricant, indium in metal state leads to reducing the friction coefficient. At the same time, when heated at cutting, indium is partly oxidized with developing of oxygen-containing phases protecting the surface when passing from the normal stage of tool wear to the avalanche-like one. This is beneficial for prolongation the stage of normal friction, considerably enhancing the tool life.

On characteristics features of alloying HSS-based deformed compound powder materials with consideration for tool self-organization at cutting 2. Cutting tool friction control due to the alloying of the HSS-based deformed compound powder material

Abstract Some approaches to friction control by alloying of new generation powder tool materials (high-speed steel (HSS) based deformed compound powder materials or DCPMs) are suggested. The first way implies reduction of self-organization level thanks to a decrease of friction coefficient at the operating temperatures. The second is realized by the addition of 5% Al 2 O 3 . On the basis of modern tribology conclusions the extension of the interval of self-organization by means of stable high-strength secondary structure developing on the tool surface is advanced as the second principal of alloying. This is implemented by employing a 2% BN (hexagonal) addition. Application of both approaches makes it possible to expect a significant total increase of tool life. This is realized by using a 20% TiCN addition.

Spatio-temporal behaviour of atomic-scale tribo-ceramic films in adaptive surface engineered nano-materials

Atomic-scale, tribo-ceramic films associated with dissipative structures formation are discovered under extreme frictional conditions which trigger self-organization. For the first time, we present an actual image of meta-stable protective tribo-ceramics within thicknesses of a few atomic layers. A mullite and sapphire structure predominates in these phases. They act as thermal barriers with an amazing energy soaking/dissipating capacity. Less protective tribo-films cannot sustain in these severe conditions and rapidly wear out. Therefore, a functional hierarchy is established. The created tribo-films act in synergy, striving to better adapt themselves to external stimuli. Under a highly complex structure and non-equilibrium state, the upcoming generation of adaptive surface engineered nano-multilayer materials behaves like intelligent systems - capable of generating, with unprecedented efficiency, the necessary tribo-films to endure an increasingly severe environment.