Search

We report a comparative study of single-layer (TiAlCrSiY)N and multilayer (TiAl-CrSiY)N/(TiAlCr)N PVD coatings on cutting tools during the break-in stage of high-speed dry cutting. Phase and chemical composition of tribooxides forming in the coating wear area were studied by X-ray photoelectron spectroscopy. It is shown that amorphous oxide films with a thickness of several dozen angstroms contain phases with a chemical composition close to mullite, sapphire, rutile, and chromium oxide. As a result of selective wear, the contact surface of the coatings retains the most durable tribooxides carrying out protective functions. Low-cycle fatigue resistance is studied using the cyclic microindentation technique. Fractal analysis of time-resolved indenter penetration depth curves combined with scanning electron microscopy (SEM) demonstrates phenomenological regularities of coatings’ damageability at the early stage of wear. It is shown that, in comparison with single-layer (TiAlCrSiY)N, the nucleation and growth of microcracks in a multilayer (TiAlCrSiY)N/(TiAlCr)N coating is accompanied by acts of microplastic deformation providing a higher fracture toughness of the (TiAlCrSiY)N/(TiAlCr)N multilayer nanocomposite.

The evolution of the self-organization process where dissipative structures are formed under the extreme frictional conditions associated with high performance dry machining of hardened steels has been studied in detail. The emphasis was on the progressive studies of surface transformations within multilayer and monolayer TiAlCrSiYN-based PVD coatings during the running-in stage of wear when self-organization process occurs. The coating layer was characterized by high resolution electron energy-loss spectroscopy (HREELS). It is shown that the nano-multilayer coating possesses higher non-equilibrium structure in comparison to the monolayer. Comprehensive studies of the tribo-films (dissipative structures) formed on the friction surface were made using a number of advanced surface characterization techniques such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES). The data obtained for the tribo-films was combined with the detailed TEM studies of the structural and phase transformations within the underlying coating layer. This data was related to the micro-mechanical characteristics of the coating layer and its wear resistance. It was demonstrated that the evolution of the self-organization process is strongly controlled by the characteristics of the tribo-films formed at different stages of the wear process. Within running-in stage (after length of cut of 15 m) fully protective mullite tribo-films predominantly form on the surface of nano-multilayer coating, establishing a functional hierarchy within the layer of tribo-films. This reduces entropy production during friction and leads to significant surface damage reduction and wear rate stabilization. In contrast, in a monolayer coating with a lower structural complexity, a variety of protective and non-protective tribo-films form during the running-in stage, which cannot fully protect the surface. Therefore the wear rate on the monolayer is not stabilized and its wear resistance is lower. The results obtained show that it is possible to control tribo-films evolution during self-organization by means of increase in structural complexity and the non-equilibrium state of the surface engineered layer with simultaneous tuning of its integrative behaviour.

A multi-functional nano-multilayered Ti0.2Al0.55Cr0.2Si0.03Y0.02N/Ti0.25Al0.65Cr0.1N physical vapor deposited (PVD) adaptive hard coatings is presented. This novel coating consists of alternating layers with variable chemical composition but similar crystal structure and hardness. A 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 (HRTEM). Various micro-mechanical characteristics (hardness, impact fatigue fracture resistance, and low cycling wear resistance) of the coating have been investigated. Oxidation resistance of the coating has been studied using Thermogravimetric–Differential Thermal Analysis (TG-DTA) within a temperature range of 25–1200 °C in air. Wear performance of the novel TiAlCrSiYN/TiAlCrN coating was evaluated through tool life studies, cutting forces measurements and identification of chips characteristics. To determine the causes of improvement in wear performance, the worn surface of the coated cutting tools was investigated using SEM/EDS. The characteristics of the surface tribo-films that were formed on the worn surface were studied using, X-ray photoelectron spectroscopy (XPS) and Extended Energy-loss Fine Spectroscopy (EELFS). One of the major features of this coating is enhanced formation of tribo-oxide films on the surface during friction. These oxides possess a sapphire and mullite structure with superb protective ability that acts simultaneously with high temperature lubricious Si–O and Cr–O phases. Due to emergent properties, the developed adaptive coating behaves as a higher ordered system under operation, capable of sustaining extreme operating conditions.

Machining of hard to cut materials such as hardened steels and high temperature strong aerospace materials is a challenge of modern manufacturing. Two categories of the aluminum-rich TiAlN-based Physical Vapor Deposited (PVD) coatings, namely AlTiN and TiAlCrN, are commonly used for this area of application. A comparative investigation of the structural characteristics, various micro-mechanical properties, oxidation resistance and service properties of the both coatings has been performed. Crystal structure has been studied using High Resolution Transmission Electron Microscopy (HR TEM). Electronic structure has been investigated using X-ray Photoelectron Spectroscopy (XPS). Micro-mechanical properties (microhardness, plasticity index, impact fatigue fracture resistance) have been evaluated using a Micro Materials Nano-Test System. Short-term oxidation resistance has been studied at 900 °C in air. The tool life of the coating was studied during ball nose end milling of hardened H 13 tool steel as well as end milling of aerospace alloys such as Ni-based superalloy (Waspalloy) and Ti alloy (TiAl6V4). It was shown that the set of characteristics that control wear performance strongly depend on specific applications. For machining of hardened tool steels, when heavy loads/high temperatures control wear behavior, the coating has to possess a well-known combination of high hot hardness and improved oxidation resistance at elevated temperatures. To achieve these properties, crystal structure for TiAlN-based coatings should be mainly B1, and elemental composition of the coating should ensure formation of strong inter-atomic bonds such as Al–Cr metal-covalent bonds in the TiAlCrN coating. Nano-crystalline structure with grain size of around 10–30 nm enhances necessary properties of the coating. In contrast, for machining of aerospace alloys, when elevated load/temperature combined with intensive adhesive interaction with workpiece material results in unstable attrition wear with deep surface damage, the coating should possess a different set of characteristics. Crystal structure for TiAlN-based coatings is basically B1; but due to a high amount of aluminum, the AlTiN coating contains AlN domains. The coating has a very fine-grained nano-crystalline structure (grains sized around 5 nm). Electron structure of energy levels indicates formation of metallic bonds. This results in plasticity increase at the cost of hot hardness reduction. The surface is able to dissipate energy by means of plastic deformation (instead of crack formation) and in this way, surface damage is reduced.

The microstructure and electronic structure of nanodispersed (Al 67 Ti 33 N) and (Ti 10 Al 70 Cr 20 N) PVD coatings were investigated by high-resolution transmission electron microscopy (HRTEM) and electron spectroscopy techniques: X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS). The grain size measured by HRTEM was 5–20 nm for Al 67 Ti 33 N and TiAlCrN type coatings, correspondingly. The spinodal decomposition of Al supersaturated nitrides under its deposition was found. Chromium increases the metastable solubility of h -AlN in c -Ti 1 − x Al x N. The lifetime of the cutting tools with Al-rich coatings has been evaluated under ball nose end milling of hardened tool steel H13 (HRC 50–52) and aerospace materials. TiAlCrN coatings are preferable for steel machining, and AlTiN coatings are better for aerospace material processing. It was found that AlTiN coating has lower hardness but higher plasticity and improved impact fatigue fracture resistance. The TiAlCrN coating has much better hot hardness and oxidation stability at high temperatures, but it is stiffer than AlTiN.

In this study the cemented carbide cutting tools with a nano-crystalline Al0.67Ti0.33N hard PVD coating deposited by cathodic arc evaporation were annealed within a range of temperatures 700–800 °C during 2 h in vacuum. The changes in structure and properties of the coating vs. temperature have been analyzed using TEM as well as high temperature nano-indentation methods. Cutting tools with the annealed AlTiN coating have been run through a number of cutting tests with varying conditions. The conditions were as following: 1) continuous cutting: turning of annealed 1040 steel (HB 220); 2) interrupted cutting: turning of 4340 steel (HRC 40); 3) end milling: ball nose end milling of hardened H13 steel (HRC 50). The cutting tool life has been investigated before and after annealing of the Al0.67Ti0.33N coatings at different temperatures. The relations between high temperature hardness and plasticity of the Al0.67Ti0.33N coating and tool life under varying cutting conditions was outlined.

Application of quaternary nitride nano-multilayered coatings results in significant improvements in tool life as well as wear behavior of ball nose end mills under severe conditions of dry high speed machining of hardened H13 steel (HRC 55–57). Tool life of different nano-multilayered TiAlCrN-based coatings with addition of transitional metals based (of V and VI groups) nitride layers has been compared. Tool life of TiAlCrN/NbN coating was found to be higher than compared to the other nano-multilayered coatings. Investigation of surface structure characteristics of the TiAlCrN/NbN coating using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and High Resolution Electron Energy Loss Spectroscopy (HREELS) has been performed. The properties of the coatings such as microhardness, modulus of elasticity, coefficient of friction and oxidation stability at elevated temperatures were also studied. Cutting forces at the tool/workpiece interface have been measured in-situ. Temperatures on the surface of cutting tools were evaluated. The features of friction and wear behavior as well as mechanisms of tribo-adaptation of TiAlCrN/NbN nano-multilayered coatings were outlined.

In this study, cemented carbide inserts with nano-crystalline Al0.67Ti0.33N coating deposited by cathodic arc evaporation, were annealed in vacuum at temperatures 700 and 900 °C during a time period of 2 h and ran through a turning test. The micro-structural characteristics, a number of micro-mechanical properties (microhardness, elastic modulus, elastic recovery parameter, microhardness dissipation parameter, critical load values during scratch testing, low cycling wear resistance) measured at room and elevated temperatures (up to 600 °C) as well as cutting tool life and wear behavior have been investigated before and after annealing using optical metallography, SEM, XRD, XPS, and HREELS methods. The results indicate the impact of microstructure formed during annealing on the mechanical and tribological properties as well as wear behavior of cutting tools with a Al0.67Ti0.33N coating.

Application of quaternary nitride (Ti,Cr,Al) N/WN nano-multilayered coatings results in a significant increase of tool life as well as wear behavior improvement under conditions of dry high-speed machining (end milling) of hardened H13 steel (HRC 50). Investigations of surface structure characteristics of TiAlCrN/WN coatings using TEM, SEM, EDX, and XPS have been performed. The microhardness, modulus of elasticity, coefficient of friction and the oxidation stability of the coatings were also studied. Cutting forces at the tool/workpiece interface have been measured in situ. It was shown that the major cause of the cutting tool life and wear behavior improvement is the enhanced tribological adaptability of a TiAlCrN/WN coating. By means of adding W to the composition of TiAlCrN/WN nano-multilayered coatings, W–O tribo-films form in synergy to alumina and provide tool life improvement.

The application of ternary nitride (Ti,Cr,Al)N coatings with high aluminum content deposited by a new plasma enhanced cathode method results in a significant cutting tool life improvement. To investigate this improvement the tool life of end milling cutting tools was studied under severe conditions associated with the high speed dry machining of H13 steel (hardness HRC 50). Investigations of the surface structure characteristics for the different compositions of TiAlCrN as well as TiAlN coatings using SEM, EDS, AES, and XPS were performed. The coefficient of friction and oxidation stability of the coatings were also measured at elevated temperatures. It was shown that the major cause of the improved cutting tool life is the adaptability of the (Ti0.10Cr0.20Al0.70)N coating under conditions experienced during high performance machining. The tribological adaptability manifests itself through the formation of complex alumina/chromia-like tribo-films on the surface of the cutting tool. This tribo-film formation serves to protect the surface of the tool and improve its lubricity during cutting. Due to the presence of these beneficial films the tendency of the workpiece material to adhere to the tool within the cutting zone is also reduced. The shape and microstructure of the chips formed during end milling were also analyzed. Both of these characteristics indicate significantly improved lubrication properties at the cutting tool/workpiece interface when the TiAlCrN coating is applied.

The main advantage of the filtered arc deposition (FAD) technique is a significant grain refinement that leads to the formation of nano-crystalline (grain size approx. 60–80 nm) PVD coatings. This technique improves the wear resistance of FAD TiAlN coatings under high-speed machining conditions when cutting tool oxidation wear is dominant. A study of the surface structure characteristics of the FAD TiAlN coatings using SEM, EDS, TEM, AES, SIMS and EELFS was performed. The microhardness of the coatings were measured. The microstructure of the chips was analyzed. The compression of the chips as well as shear angle was measured. The friction parameter on the rake surface of the tools was determined in-situ. It was shown that the major cause of the high wear resistance of the FAD coatings during high-speed machining was the formation of the thin protective oxide films on the cutting tool surface. The grain size refinement of the coating promotes the formation of protective alumina films. These films are formed at the surface of nano-crystalline FAD TiAlN coating during high-speed machining. They mainly consist of protective alumina, whereas the films that are forming on the surface of TiAlN commercial coatings with coarser grains consist only of non-protective titania. The formation of the protective alumina films, composed of complicated amorphous–crystalline structures, significantly improves the friction and wear performance of coated tools. The tendency of the work piece material to adhere is reduced and considerably more heat is dissipated via chip removal. This is a major cause of the enhanced wear resistance of the FAD coating technique. Tribo-oxidation during cutting is a typical process of the self-organization of TiAlN coatings that results in a quasi-stabilization of cutting tool wear. The self-organization and friction control for coated cutting tools is considered based on a non-equilibrium thermodynamic approach.

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.

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.

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 wear in tools made of high-speed steels with surface engineered coatings incorporating ion nitriding and (Ti, Cr) nitride CAPDP (cathode arc plasma deposition process) coatings were investigated at increased cutting speeds in the vicinity of 50–100 m min−1. The wear kinetics, the change of micro-relief of cutter surface and the depth of the unhardened zone of cutting indexable inserts made of high-speed steels with surface engineered coatings were studied. A significant tool life was found for the surface engineered high-speed steel under the greatest possible localization of thermomechanical effects in the CAPDP coating layer. The application of a surface engineered system composed of a heat resistant high-speed steel T15 (P12M3φ2K5) substrate, with surface modified by ion nitriding and then by CAPDP (Ti, Cr) N coating, provides this result.

Changes in chemical composition and fine (at atomic level) structure characteristics of surfaces during the life time of cutting tools were investigated by using AES, SIMS and EELFAS methods. High-speed steels M2 and T15 with coatings incorporating ion nitriding and (Ti, Cr) nitride CAPDP (cathode arc plasma deposition process) were used. It was found that, under the wear conditions studied (such as cutting of medium carbon steels), some components of the protective hard coating dissociated, forming quasi-oxide amorphous films. This shows the parallel developing processes of: 1. Dissociation of chemical compound in coating material (Ti, Cr) N and intensive diffusion (absorption) of nitrogen into chip. 2. Creation on tool surface of stable amorphous protecting quasi-oxide TiO films. The discovered changes in chemical and phase composition of contact surfaces of the “tool-workpiece” tribopair improve service characteristics of the cutting tool and promote its adaptation to service conditions (named “self-organization”). The adaptation observed is expressed more on steel T15 with high heat resistance and leads to a significant increase of tool life.

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.

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 the major physical-chemical processes during cutting are mostly concentrated within a layer of the tribo-films. This nano-tribological phenomenon produces beneficial heat distribution at the chip/tool interface which controls the tool life and wear behavior.Results of x-ray photoelectron spectroscopy studies indicate enhanced formation of protective sapphire- and mullite-like tribo-films on the friction surface of the multilayer TiAlCrSiYN/TiAlCrN coating. Comprehensive investigations of the structure and phase transformation within the coating layer under operation have been performed, using high resolution transmission electron microscopy, synchrotron radiation technique: x-ray absorption near-edge structure and XRD methods.The data obtained show that the tribo-films efficiently perform their thermal barrier functions preventing heat to penetrate into the body of coated cutting tool. Due to this the surface damaging process as well as non-beneficial phase transformation (formation of AlN hex phase) drastically diminishes within the layer of the adaptive coating. Micro-mechanical properties measurements performed at room and elevated temperatures show that the hardness of the multilayer TiAlCrSiYN/TiAlCrN coating appears stable to 500 °C and then drops a little at 600 °C but still remains high. It means that if the surface tribo-films can reduce actual temperature down to this level the coating underneath is able to efficiently withstand heavy loads under operation.

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 ...