Nanoscale Multilayer Coatings Research Articles

Increased Operating Properties of Cutting Ceramics by Application of Nanostructured Multilayer Wear-Resistant Coating

This paper presents the results of the development of nanoscale multi-layered composite coatings for improving the contact performance of ceramic cutting tools. These nanocoatings help reducing brittle fracture of cutting edges and ensure a balanced wear of tool contact areas during dry high-speed machining of hardened steels. A filtered cathodic vacuum arc deposition process was used to generate the nanoscale multi-layered composite coatings (NMCC) with improved physical and mechanical properties and adhesion strength to ceramic substrate. In this work, thermodynamic criteria were used to evaluate the selected composition of NMCC, and the crystal-chemical, physical, mechanical and cutting properties and wear mechanisms were studied. Ti-(TiAl)N-(ZrNbTiAl)N coating was deposited on Al2O3, Al2O3-TiC and Si3N4 ceramic substrates. Test results showed that the wear mechanism of the coated tool was predominantly due to adhesive-fatigue processes. The development of wear was observed to be centered on the rake and flank faces of the tool without brittle chipping. The results of high-speed longitudinal turning of hardened steel X153CrMoV12 showed an increase in tool life by a factor of 1.5 against the uncoated tools and a factor of 1.3 compared with standard PVD coating Ti-(TiAl)N.

CrVN/TiN nanoscale multilayer coatings deposited by DC unbalanced magnetron sputtering

The growing interest in development coatings with enhanced properties opened the door to the research and development of nanoscale multilayer coatings. Some of the most interesting properties of these multilayer coatings when compared to monolayers are hardness higher than 40GPa, friction coefficients <0.3, improved adhesion and increased heat and corrosion resistance.In this work, CrVN/TiN nanoscale multilayer coatings were deposited onto H13 steel substrates by DC unbalanced magnetron sputtering. For the deposition of the multilayer coatings, two targets of Cr-V (70–30wt%) and Ti (99.5wt%) confronted opposite each other were used. In order to vary the bilayer period, a microcontroller was used to control the rotation and residence time of the substrates in front each target, thereby obtaining multilayer periods of 15nm, 30nm and 43nm. CrVN and TiN monolayer coatings were also deposited.X-ray diffraction (XRD) showed a FCC crystal structure for all coatings. SEM images revealed a columnar structure for CrVN and a cauliflower-like structure for TiN, similar to that obtained for the multilayer coating. All coatings showed a Hardness and Young's modulus around 19GPa and 270GPa, respectively. The CrVN/TiN multilayer with a period of 15nm showed the lowest friction coefficient (0.31) and the lowest wear rate (2.23×10−9kg/Nm) of all coatings, representing a reduction of 36% compared to the friction coefficient of H13 steel and a reduction in the wear rate of three orders of magnitude compared to the TiN. Finally, it was possible to identify three stages in the wear mechanism in the multilayer coatings, the lowest period, molecule-to-molecule adhesive wear occurred, followed by a rupture in the TiN and CrN bonds when the period increased to 30nm, while with the highest period of 43nm, oxides of titanium, chromium and vanadium were formed.

Effect of chamber pressure on defect generation and their influence on corrosion and tribological properties of HIPIMS deposited CrN/NbN coatings

It has been reported that compared to state-of-the-art technologies, High Power Impulse Magnetron Sputtering produces very dense and droplet free coatings due to the high plasma density and ionisation rate. However, thorough investigation of the coating morphology by scanning electron microscopy, optical microscopy and other surface analysis methods revealed the existence of various types of coating defects.This study reports the influence of chamber pressure in particular on defect formation in CrN/NbN nanoscale multilayer coatings. The coating series was deposited using combined HIPIMS/UBM technique while varying the total chamber pressure from 0.2Pa to 1Pa. Four types of defects were identified, namely, nodular, open void, cone-like and pinhole. Defect density calculations showed that the coating produced at the lowest pressure, 0.2Pa, had the lowest defect density of 0.84%.As expected coating corrosion properties improved linearly with decreasing defect density. Potentiodynamic polarisation corrosion studies revealed that in the potential range of −300mV to +300mV, the current density decreased with decreasing defect density (from 5.96% to 0.84%). In contrast, pin-on-disk tribology tests at room temperature demonstrated that the tribological properties of the coatings deposited at different chamber pressures were dependent on the crystallographic orientations and on the nature of the oxides formed at the tribological contact. Coatings with (200) crystallographic orientation had lower wear rates (~1.6×10−15m3N−1m−1) whereas coating with (111) crystallographic orientation had the highest wear rate (2.6×10−15m3N−1m−1). Friction properties were influenced by the tribolayer formed during the tribological tests.However, for the coatings deposited at same chamber pressure of 0.35Pa but with different defect densities (due to the difference in chamber cleanliness), the friction behaviour was directly influenced by the coating defects. The friction co-efficient (μ) decreased by a factor of two from 0.48 to 0.25 when the defect density decreased from 3.18% to 1.37%.

Improving thermal stability of TiSiN nanocomposite coatings by multilayered epitaxial growth

Owing to the superior mechanical properties, nanoscale multilayer coatings are regarded as excellent protective layers for machining applications. Here, the effect of multilayer architecture on the structure and thermal stability of TiSiN nanocomposite coating is investigated. Corresponding to the TiSiN nanocomposite coating with nanocrystalline grains encapsulated by the amorphous matrix, TiSiN/TiN coating, consisting of 6.6nm TiN and 3.7nm TiSiN layers, exhibits the epitaxial growth with coherent interfaces and thus results in a complete Si-solution of TiSiN sublayers. The coherency strains in multilayer retard the thermal decomposition behavior of TiSiN sublayers. Therefore, the hardness of TiSiN/TiN multilayer can be maintained at ~38.9GPa upon annealing to 1100°C, where the hardness of TiSiN coating already decreases from as-deposited ~40.6GPa to ~36.2GPa due to the grain coarsening and the thermal decomposition.

The effect of modulation period on the mechanical and wear properties of TiAgN/W2N coatings

TiAgN/W2N nanoscale multilayered coatings with various modulation periods from 1.0 to 9.0nm were prepared by alternating deposition of TiAgN and W2N. The microstructure, hardness and wear performances were analyzed by XRD, HRTEM, nano-indentation CSM, SEM, Raman and Bruker profilometer. The maximum hardness, 27.6GPa, was obtained for the TiAgN/W2N nanoscale multilayered coating with modulation period of 2.0nm, which is an increase of 72.5% over the rule of mixture hardness value (16.0GPa) of TiAgN and W2N coatings. The wear resistance of TiAgN coating was improved greatly by nanoscale multilayered structurization with W2N due to the higher hardness. With increasing the tested temperature, the increase of the wear rate of TAW coatings is attributed to the increase of these oxides.

Nano-scale multi-layered coatings for improved efficiency of ceramic cutting tools

This paper considers improving the efficiency of ceramic cutting tools using nano-scale multi-layered composite coatings deposited with an innovative arc-PVD processes with filtration of vapour-ion flow and diamond-like coating (DLC). Here a three-layered architecture of nano-structured multi-layered composite coatings is used, and the wear mechanism of the ceramic tool is examined. This approach allows implementing a direct control over the contact characteristics of the cutting process in order to reduce the normal and shear stresses that increase the probability of tool failure as a result of brittle fracture. This increases the adhesive strength of the coating with respect to the ceramic substrate. This resulted in an increase in tool life with reduced failure rate because of brittle fracture of the cutting edge.

Edge Cutting Tools for Machining of Hard-to-Cut Materials

The study considers the possibility to increase the efficiency of cutting of hard-to-cut materials through the use of innovative tool materials of layer composite type with nanoscale multi-layer composite coatings and carbides with cobalt-rhenium refractory binder. The effect of the increase in the tool life was achieved through higher wear resistance of cobalt-rhenium solid carbide to thermoplastic fracture and wear at elevated temperatures. For synthesis of coatings, the process of filtered cathodic vacuum-arc deposition (FCVAD) and the control technology on its basis were used for high-performance surface preparation and application of nanostructured coatings of multi-layer complex composite architecture on WC-Co, WC-(Co/Re) carbides. During the study, the mathematical models of the FCVAD processes are developed to optimize the numerical values of the basic parameters of the deposition technology, including operating gas pressure, value of cathode current, and voltage on substrate.

Influence of electronic structure, plasmon-phonon and plasmon-polariton excitations on anomalously low heat conductivity in TiAlN/Ag nanoscale multilayer coatings

TiAlN/Ag multilayer coatings with different number of bilayers and thicknesses of individual layer were fabricated by DC magnetron sputtering. Thermal conductivity and electronic structure features were measured on a set of samples with different number of bilayers and individual layer thickness from a 5–150 nm for total coating thickness of ∼0.5 or 1 μm. It was found that thermal conductivity of the multilayer insulator/metal structure becomes lower than for monolithic TiAlN coatings with the same thickness when Ag layers are thinner than 25 nm. The physical nature of thermal barrier properties of the nanolaminate TiAlN/Ag films is studied using X-ray photoelectrons (XPS) and high-resolution electron-energy loss (HREELS) spectroscopies. Based on these results, a physical model for the anomalous decrease in heat conductivity for nanoscale multilayers was developed on base of analysis of plasmon and lattice vibrations inside the layers and at the interfaces. Anomalously low heat transfer is attributed to attenuation of longitudinal acoustic phonons vibrations, decreasing of plasmon-polariton penetration on interfaces, and plasmon states splitting in Ag nanolayers due to confinement effects at multilayer coatings nanostructuring.

Improvement of structure and quality of nanoscale multilayered composite coatings, deposited by filtered cathodic vacuum arc deposition method

This article studies the specific features of cathode vacuum arc deposition of coatings used in the production of cutting tools. The detailed analysis of the major drawbacks of arc-Physical Vapour Deposition (PVD) methods has contributed to the development of the processes of filtered cathodic vacuum arc deposition to form nanoscale multilayered composite coatings of increased efficiency. This is achieved through the formation of nanostructure, increase in strength of adhesion of coating to substrate up to 20%, and reduction of such dangerous coating surface defects as macro- and microdroplets up to 80%. This article presents the results of the studies of various properties of developed nanoscale multilayered composite coating. The certification tests of carbide tool equipped with cutting inserts with developed nanoscale multilayered composite coating compositions in longitudinal turning (continuous cutting) and end symmetric milling, and intermittent cutting of steel C45 and hard-to-cut nickel alloy of NiCr20TiAl showed advantages of tool with nanoscale multilayered composite coating as compared to the tool without coating. The lifetime of the carbide inserts with developed NMCC based on the system of Ti–TiN–(NbZrTiCr)N (filtered cathodic vacuum arc deposition) was increased up to 5–6 times in comparison with the control tools without coatings and up to 1.5–2.0 times in comparison with nanoscale multilayered composite coating based on the system of Ti–TiN–(NbZrTiCr)N (standard arc-PVD technology).

Research of the cutting of materials used in heavy power engineering by means of the carbide cutting tools with nanoscale wear-resistant coating

The paper presents the results of the studies focused on the specifics of cutting of materials, used in manufacturing of heavy power engineering products, on the example of longitudinal turning of steel 9SiMn16. To improve such important parameters of cutting as tool life and reliability of carbide tools, it is proposed to use nanoscale multilayer composite coatings, in particular, Ti-TiN-(TiCrAl)N and Zr-ZrN-(ZrNbCrAl)N, produced using the filtered cathodic vacuum arc deposition (FCVAD). It was found out that the use of carbide tools with developed coatings results not only in reduction of cutting forces by 20-25%, but also in substantial reduction of force variation as compared with the corresponding parameters for uncoated tools, which allows improvement of cutting quality. The proposed nanoscale multilayer composite coatings provide significant increase in tools useful life as compared with the standard TiN coating.

Multilayer composite nanoscale coatings as a method to increase reliability and tool life of cutting tools made of mixed ceramic Al2O3-TiC

The paper studies the challenges of improvement of reliability and tool life of ceramic cutting tools made of mixed ceramic Al2O3-TiC through application of nanoscale multilayer composite coatings, deposited through the method of filtered vacuum arc deposition. The paper studied wear mechanisms of ceramic cutting tools with and without coatings, as well as reliability of ceramic tools. It is found out that coatings reduce the wear rate of a ceramic tool along its flank face. The difference between flank wear land VB for an uncoated ceramic tool and a ceramic tool with coating reaches up to 60 μm during cutting time of 10–12 min, with the better results on reduction of the wear rate of flank wear land shown by ceramic cutting inserts with nanoscale multilayer coating Ti-(TiAl)N-(TiCrAl)N as compared with coating Ti-(TiAl)N-(ZrNbTiAl)N. The tests showed that failures of uncoated ceramic tools follow the exponential distribution law, and the coefficient of failure variation of such tool is 1.08. Meanwhile, the failures of coated ceramic tools follow the law of Weibull distribution, and the coefficients of failure variation are 0.39–0.45, respectively. Thus, it is found out that the deposition of multilayer composite coatings of recommended composition on working surfaces of a tool equipped with cutting inserts of mixed ceramic Al2O3-TiC provides the increased operating reliability of the ceramic tool and predicts its failures.

Heat transfer through nanoscale multilayered thermal barrier coatings at elevated temperatures

Heat transfer through thermal barrier coatings (TBCs) composed of alternating nanometer thick layers of aluminum oxide and 7% yttria stabilized zirconia (7YSZ) was studied by pulsed heating at temperatures in the range 1275K to 1375K. The thermal diffusivity of the TBCs, deposited on thin metal foils by electron beam evaporation and coated with an opaque, submicrometer metal capping layer, was studied by applying a sub-μs duration heating pulse from a Q-switched laser to the substrate and then monitoring the temperature rise on the opposing, metal-capped surface of the TBC. The recorded temperature transients were modeled using properties of the constituent materials in order to obtain an upper bound of the thermal resistance associated with the interfaces between layers. The results thus provide insight into the feasibility of using interfacial thermal resistance in this material system to improve TBC performance by decreasing thermal conductivity.

Effect of Different TiO2-SiO2 Multilayer Coatings Applied by Sol-Gel Method on Antireflective Property

Multilayer thin films prepared using the sol-gel process have been used in many antireflection applications. In this paper, antireflective nanoscale multilayer TiO2-SiO2 coatings were formed on both sides of the glass substrates by combining sol-gel method and dip coating techniques. The coatings were carried out using tetraethyl orthosilicate as precursor for SiO2 and tetrabutyl orthotitanate as precursor for TiO2. The coatings prepared in this work were characterized using scanning electron microscope, Fourier-transformed infrared spectrophotometer and UV-Visible spectrophotometer. The SiO2 top layer coatings showed excellent antireflection in the wavelength range of 400-800 nm where the transmittance of glass substrate is significantly lower. By increasing the number of double TiO2-SiO2 layers, the transmission of the coated glasses increased due to applied multilayer coating properties. Six-layer sol-gel TiO2-SiO2 coatings showed the highest visible transmittance about 99.25% at the band of 550-650 nm.

A study of the cutting properties and wear mechanism of ceramic edge tools with nanostructure multilayer composite coatings

The paper presents the results of studies of the cutting properties and wear mechanism of the edge cutting tool equipped with replaceable indexable inserts made of cutting ceramic with nanoscale multilayer composite coatings when cutting hardened steel. It has been shown that applying the latter allows one to tune the contact processes based on the changes in friction and lengths of dense and complete contacts between the chip and the rake face of the cutting tools, thereby reducing normal contact strains and the probability of macro- and microbrittle fracture in the contact areas of the tool.

Improving the Efficiency of Carbide End Mills by Deposition of Nano-Scale Multi-Layered Composition Coatings

The study has considered the challenge of improving the efficiency of carbide end mills through modification of the physical and mechanical properties of tool by forming on its working surfaces nanostructured multi-layered composite coatings with use of filtered cathodic vacuum arc deposition (FCVAD). The technique of deposition of three-component multi-layered composite coatings with nanosized grain structure and thickness of sublayers on working surfaces of end mills has been developed. The developed coatings contain three key components, each of which has a strictly functional purpose specifying enhanced wear resistance, strong adhesive bonding with tool material and barrier properties with regard to heat flows and diffusion, and that allows improving the efficiency of carbide end mills. The study has found out that when carbide end mills with developed coatings are used at cutting, the cyclic thermomechanical stresses acting on the cutting part of the tool during the cutting stroke and idle run of cutting edge of end mills are smoothed, and that leads to the decrease in the rate of tool wear and improves the efficiency of carbide end mills. The study was supported by grant No. 9.251.2014/K, project code 251.

Size effects in the mechanical response of nanoscale multilayer coatings on glass

Very thin (100–400nm) oxide coatings which are used as antireflection and barrier layers in low emissivity architectural glass have been studied by nanoindentation methods to determine the effect of coating thickness on mechanical response. Whereas plasticity (hardness) is relatively easy to assess the elastic response of the coating is underestimated as the thickness is reduced. Thus, although some changes are observed with thickness, there is no size effect in elasticity. Size effects in plasticity are only observed for the crystalline layers such as ZnO whereas the other oxides deposited in this study were amorphous and show no size effect. Traditional microindentation-derived methods to determine the fracture toughness are unsuitable for assessing very thin coatings (<500nm) and alternative energy-based models are required depending on what features are visible in indentation load–displacement curves. For oxide coatings no size effects in fracture toughness were observed, however there are process-induced variations in residual stress which will affect the apparent fracture and adhesion strengths of the coatings. Failure by delamination during scratching depends on the magnitude of the applied stress which in turn depends on the thickness of coating layers deposited. This is because the friction tractions are controlled by the surface roughness which increases with coating thickness.

Tribological and mechanical properties of Ti/TiAlN/TiAlCN nanoscale multilayer PVD coatings deposited on AISI H11 hot work tool steel

A new [Ti/TiAlN/TiAlCN]5 multilayer coatings were deposited onto polished substrate AISI H11 (DIN 1.2343) steel by an industrial magnetron sputtering device. The tribological performance of the coated system was investigated by a ball-on-disk tribometer against 100Cr6 steel and Al2O3 balls. The friction coefficients and specific wear rates were measured at various normal loads (2, 5, 8, and 10N) and sliding velocities (0.2, 0.4, and 0.8m/s) in ambient air and dry conditions. The phase structure, composition, wear tracks morphologies, hardness, and film/substrate adhesion of the coatings were characterized by light-microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), 3D-surface analyzer, nanoindentation, and scratch tests. Results showed that the deposited coatings showed low wear rates in the scale of 10−15m3/Nm, low friction coefficients against 100Cr6 and Al2O3 balls in the range of 0.25–0.37, and good hardness in the range of 17–20GPa. Results also revealed that the friction coefficients and disc wear rates decrease and increase, respectively with the increase in normal load and sliding velocity for both coating/Al2O3 and coating/100Cr6 sliding system. Compared with the uncoated-H11 substrate, the deposited coating exhibited superior tribological and mechanical properties. The dominant wear mechanism was abrasive wear for coating/Al2O3 pair, while for coating/100Cr6 pair, a combination of mild adhesive wear, severe adhesive wear, and abrasive wear (extensive plowing) were the dominant wear mechanisms at different applied normal loads.

Nano-scale multilayered-composite coatings for the cutting tools

In machining, the tool life is one of the limiting criteria in the process; therefore, the development of wear-resistant material for the cutting tools is imperative. This paper presents a methodological approach to the design of nano-scale multilayered-composite coatings for cutting tools. A plasma-enhanced technology of filtered cathodic vacuum-arc deposition is used to coat the tools, which significantly extends the operational life of the cutting tools. Here, a three-layered architecture of coatings is proposed and each layer has a specific function. The engineered structural layers allowed for optimum combination of a high adhesion strength with the tool substrate and a minimum adhesion of the work material to the tool surface. The coating process is presented here alongside with the technological role of the layers. A study of the effect of the developed nano-scale multilayer composite coatings on the rates of tool wear was undertaken, and results were compared with the wear rates of uncoated and standard coatings. The results of a wide range experimental work are given in terms of flank wear and tool life for various machining conditions.

Nano-scale Multilayered Composite Coatings for Cutting Tools Operating under Heavy Cutting Conditions

The aim of this work was to create a methodology for the development of wear-resistant coatings. These coatings were deposited on the working surfaces of carbide inserts which were used for rough re-profile machining of railway wheels-sets. The coatings were formed using a filtered cathodic vacuum arc deposition (FCVAD). An investigation into the effect of the FCVAD process parameters on the composition and properties of the coatings was undertaken. The experimental work replicated industrial application conditions in terms of cutting speed (40- 80 m/min), feed rates (0.8-1.2mm/rev) and depth of cuts (4.0-8.0mm). An increased tool life was achieved using carbide inserts with nanostructured multilayer composite coatings based on the Ti-TiN-TiAlCrN compound. The paper presents the results of carbide inserts with newly developed coatings for heavy duty machining of railway wheel-sets. The main coatings parameters i.e. microhardness, thickness, strength of adhesion of “coating-substrate” and surface morphology were studied. The nano-scale grain structure and thickness of sublayers for each coating component allowed achieving a balanced wear of rake and flank surfaces without micro/macro chipping of contact areas and cutting edge of the inserts. The results presented here show that the cutting tool life of the inserts with the new wear-resistance coatings exceeded commercial coated tools by a factor of more than two.

Improving the Efficiency of the Cutting Tools Made of Mixed Ceramics by Applying Modifying Nanoscale Multilayered Coatings

The paper studies the influence of properties of a tool made of mixed ceramic by applying modifying with nanoscale multi-layered coatings on machinability of hardened tool steel XVG. The paper also examines the influence of cutting speed on wear resistance of mixed ceramic with nanoscale multilayered coatings. The mathematical models that found out the dependence of tool life of a ceramic tool with coating from cutting speed were developed.