Cathodic Arc Deposition Research Articles

Comprehensive microstructural and optical characterization of the thermal stability of aluminum-titanium oxynitride thin films after high temperature annealing in air

The thermal stability of two AlyTi1-y(OxN1-x) layers prepared by cathodic vacuum arc deposition with different oxygen content was studied after high temperature annealing of the samples in air. These layers were designed to be part of solar-selective coating (SSC) stacks. Compositional and microstructural characterization of the thin films was performed before and after the thermal treatment by elastic recoil detection (ERD), transmission electron microscopy, and Raman spectroscopy. AlyTi1-yN sample was stable after 2 h of annealing at 450 °C. Initial stages of the formation of a surface oxide layer after annealing at 650 °C were observed both by ERD and Raman analysis. Contrarily, no changes were found after 2 h annealing treatment either at 450 and 650 °C in the composition and microstructure of AlyTi1-y(OxN1-x) sample. In both samples, the formation of a surface anatase TiO2 film was reported after 2 h annealing at 800 °C. These compositional and microstructural changes were correlated with the optical properties determined by spectroscopic ellipsometry. A transition from metallic to dielectric behavior with increasing annealing temperature was observed. These results complete the durability studies on the designed SSC based on AlyTi1-y(OxN1-x) materials, confirming that these stacks withstand breakdown at 600 °C in air.

Enhancement of discharge and deposition rate by imposed pulse current during the cathodic arc deposition of ta-C films

The deposition rate of ta-C films was increased by imposed pulse cathodic arc deposition (IP-CAD). The arc discharge behavior, deposition rate and micro-hardness of the ta-C films were investigated at average arc currents (Iaverage) ranging from 60 A to 100 A. The average substrate current density of IP-CAD was higher than that of DC-CAD at the same Iaverage. The optical emission spectra demonstrated that a dramatic increase in the evaporation rate of both carbon atoms and ions were achieved by imposing high pulsed current with Iaverage of 80 A. As the IAverage increased from 60 A to 100 A, the deposition rate increased by about 110% for the IP-CAD and by 33% for DC-CAD. This might be attributed to the cooperative actions of high evaporation rate of the carbon, large arc pressure near the arc spots and the focusing effect induce by high current. As compared to DC-CAD, the IP-CAD mode led to smaller concentration of sp3 (44%) than DC-CAD (59%) at the IAverage of 80 A. However, the IP-CAD ta-C films exhibited higher micro-hardness (~44.7 GPa) than that of DC-CAD (24 GPa). A preferable toughness was simultaneously obtained for IP-CAD.

Microstructuring technology for large and cylindrical receivers for concentrated solar plants (CSP)

This paper presents an innovative fabrication process of microstructured spectrally selective solar absorbers for concentrated solar power (CSP) plants. The authors describe suitable technologies and methods to microstructure large areas and non-conventional substrates, such as tubes, and substrates with large surface areas typically used in CSP plants. Specific colloidal lithography combined with layer deposition makes it possible to structure this type of substrate with a submicron periodicity within a hexagonal arrangement. Appropriate techniques, e.g. Langmuir-Blodgett deposition and customized UV insolation were developed to process 80 mm diameter and 300 mm long tubes and 300 × 300 mm2 planar substrates. Absorbing and anti-reflection coatings were deposited using industrial vacuum deposition equipment with three different deposition sources: PECVD, magnetron sputtering and cathodic arc deposition. The design and assessment of the efficiency of the microstructure absorbing layers on smaller planar substrates are described elsewhere, assuming that optical performances are close to the large and tubular substrates. The technological processes and the resulting demonstrators are described in detail herein.

Effect of annealing on structural, mechanical and tribological properties of Cr-(CrN/TiAlN) coating

ABSTRACT TiAlN film was deposited with Cr-CrN interlayer (Cr-(CrN/TiAlN)) on DAC-10 tool steel using cathodic arc deposition followed by annealing in vacuum chamber at 700°C temperature. Nanoindentation and nanoscratch test were conducted on as-deposited and annealed samples. The annealed samples showcased improved hardness (8.55 %) and elastic modulus (12.21 %) attributed to the formation of larger grain size (48 nm) and diffusion of Cr atoms from the interlayer. The XRD pattern of the annealed samples revealed Cr diffusion in the TiAlN top layer along with the formation of oxide such as Al2O3. The annealed samples registered lower pile up, indentation depth, higher strain hardening exponent (n = 0.41) and lower plastic work (0.25). Tribological properties such as scratch hardness was improved by 8.84%, whereas coefficient of friction and wear rate was reduced by 22.92% and 35.75%, respectively, after annealing of the coating. The relation between the nanomechanical and scratch properties was indicative of the influence of hardness and strain hardening exponent on the wear properties of the annealed Cr-(CrN/TiAlN) coating.

Cathode spot behavior in nitrogen and oxygen gaseous atmospheres and concomitant cathode surface modifications

The cathode spot behavior influences the arc plasma chemistry and film growth conditions during reactive cathodic arc deposition of nitride and oxide films. Cathode spots can be studied using their characteristic craters left behind on the cathode surface. The multilayer cathode design used in this study reveals temporal and spatial progress of cathode spots by enabling three-dimensional visualization of the craters. The surface nitridation or oxidation of the cathode, also known as cathode poisoning, was found to give rise to a repeated switching between cathode spots of type 1 and 2. The surface oxide layers, however, more significantly promote the ignition of type 1 spots due to their thermodynamically privileged formation and/or their more favorable physical properties building up a stronger electric field within the insulating layer. The crater depths and their contribution to the surface modification of multilayered cathodes are discussed in detail. These results may contribute to a better understanding of macroparticle generation and arc plasma properties in cathodic arc deposition processes.

Thermal stability and diffusion characteristics of ultrathin amorphous carbon films grown on crystalline and nitrogenated silicon substrates by filtered cathodic vacuum arc deposition

Amorphous carbon (a-C) films are widely used as protective overcoats in many technology sectors, principally due to their excellent thermophysical properties and chemical inertness. The growth and thermal stability of sub-5-nm-thick a-C films synthesized by filtered cathodic vacuum arc on pure (crystalline) and nitrogenated (amorphous) silicon substrate surfaces were investigated in this study. Samples of a-C/Si and a-C/SiNx/Si stacks were thermally annealed for various durations and subsequently characterized by high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The TEM images confirmed the continuity and uniformity of the a-C films and the 5-nm-thick SiNx underlayer formed by silicon nitrogenation using radio-frequency sputtering. The EELS analysis of cross-sectional samples revealed the thermal stability of the a-C films and the efficacy of the SiNx underlayer to prevent carbon migration into the silicon substrate, even after prolonged heating. The obtained results provide insight into the important attributes of an underlayer in heated multilayered media for preventing elemental intermixing with the substrate, while preserving the structural stability of the a-C film at the stack surface. An important contribution of this investigation is the establishment of an experimental framework for accurately assessing the thermal stability and elemental diffusion in layered microstructures exposed to elevated temperatures.

Investigation of the properties of Ti-TiN-(Ti,Al,Nb,Zr)N composite coating and its efficiency in increasing wear resistance of metal cutting tools

The paper investigates the structure and the elemental and phase composition of Ti-TiN-(Ti,Al,Nb,Zr)N coatings, deposited using Filtered Cathodic Vacuum Arc Deposition (FCVAD) technology. The coating under study has a nanolayer architecture of outer (wear-resistant) material with a nanolayer thickness of 2–10 nm and ternary period of λ = 180 nm. The experiments found that the wear-resistant coating layer was composed of a main cubic phase of (Ti,Nb,Zr,Al)N with the space group -Fm3m, as well as very small amounts of a h-AlN phase with the space group P6.3mc. The distribution of elements within the ternary period varies in a wide range due to the planetary rotation of the substrate (Al varies within 1–20 at.%, Ti – 5-70 at.%, Zr – 3-30 at.%, and Nb – 3-40 at.%). The investigation includes comparative cutting tests of tools with the coating under study, as well as tools with Ti-TiN-TiAlN coatings with high (55 at.%) and low (16 at.%) aluminum content, and uncoated tools. The study considers the specifics of the wear patterns on carbide tools during the turning of workpieces made of AISI 1045 steel. The investigation is focused on the specifics of diffusion processes in the area of the interface of the coating and the material being machined. Both the diffusion of iron into the coating structure (to a depth not exceeding 100 nm) and the diffusion of coating elements (primarily titanium) into the structure of the material being machined (to a depth not exceeding 200 nm) are detected.

A Comprehensive Study of Al0.6Ti0.4N Coatings Deposited by Cathodic Arc and HiPIMS PVD Methods in Relation to Their Cutting Performance during the Machining of an Inconel 718 Alloy

The structural, physical–chemical, and micromechanical characteristics of Al0.6Ti0.4N coatings deposited by different physical vapor deposition (PVD) methods, such as cathodic arc deposition (CAD), as well as advanced HiPIMS techniques were investigated in terms of their cutting performance during the machining of an Inconel 718 alloy. XRD studies had revealed that the HiPIMS coating featured lower residual stresses and more fine-grained structure. Electrochemical characterization with the potentiostat-impendence method shows that the HiPIMS coating has a significantly lower porosity than CAD. SEM and AFM studies of the surface morphology demonstrate that the HiPIMS coating has a smoother surface and an absence of droplet phases, in contrast with CAD. XRD, combined with FIB/TEM studies, shows a difference in the crystal structure of both coatings. The micromechanical characteristics of each coating, such as hardness, elastic modulus, fracture toughness, and adhesion to the substrate, were evaluated. The HiPIMS coating was found to possess a more beneficial combination of micromechanical properties compared to CAD. The beneficial characteristics of the HiPIMS coating alleviated the damage of the coated layer under operation. Combined with grain size refinement, this results in the improved adaptive performance of the HiPIMS coating through the formation of a greater amount of thermal barrier sapphire tribo-films on the friction surface. All of these characteristics contribute to the reduction of flank and crater wear intensity, as well as notching, leading to an improvement of the HiPIMS coating’s tool life.

Steam oxidation behavior of ZrO2/Cr-coated pure zirconium prepared by plasma electrolytic oxidation followed by filtered cathodic vacuum arc deposition

Plasma electrolytic oxidation (PEO) and filtered cathodic vacuum arc deposition (FCVAD) techniques were employed to fabricate a ZrO2/Cr composite coating on pure zirconium. The steam oxidation properties of bare and ZrO2/Cr-coated pure Zr were performed in water vapor environment at 900–1100 °C. Their morphologies, microstructures and phase constituents before and after steam oxidation were analyzed. Meanwhile, their composition depth profiles were measured by glow discharge optical emission spectroscopy (GDOES). It was found that the mass gain of ZrO2/Cr-coated Zr was about 22–45% of that of bare Zr after 3600 s steam oxidation at 900–1100 °C, and the PEO and FCVAD composite treatments significantly improved the steam oxidation resistance of Zr. After steam oxidation, the phosphorous element in the outer layer of PEO film from phosphate electrolyte diffused into the residual Cr layer, however, most of the phosphorous in the interior of PEO layer was remained although the phosphorus diffusion in the region was accelerated with the increase of steam temperature. The ZrO2 to Zr3O phase transformation in PEO intermediate layer occurred in high temperature steam. Furthermore, the PEO zirconia interlayer suppressed hydrogen permeation into the Zr substrate during steam oxidation at 900–1100 °C.

Influence of pulsed-substrate bias duty cycle on the microstructure and defects of cathodic arc-deposited Ti1-xAlxN coatings

The influence of pulsed substrate bias duty cycle on the growth, microstructure, and defects of Ti 1-x Al x N coatings grown by cathodic arc deposition was investigated. Ti 1-x Al x N coatings of varying compositions (x = 0.56, 0.38, 0.23) were deposited on cemented carbide substrates with 10, 25, 50, and 95% duty cycles of −50 V pulsed-bias under 10 Pa of pure N 2 gas. Coatings grown at low duty cycles (10 and 25%) showed strongly textured, under-dense coatings with facetted columns and low amount of lattice defects. Applying higher duty cycles (50 and 95%) produced coatings that have denser microstructures, less preferred orientation, increasing compressive stresses and increased lattice defect densities. Our study elucidates how duty cycle variation not only changes the overall average energy supplied at the growth front but also kinetically influences the coating growth and thus microstructure and defect structure. • Ti 1-x Al x N coatings were grown on WC-Co substrates with 10, 25, 50, and 95% duty cycles of -50 V pulsed-substrate bias. • Duty cycle variation significantly and systematically affected their growth, microstructure, and crystallographic defects. • Low duty cycle conditions produced textured, under-dense coatings with facetted columns and low amount of lattice defects. • Higher duty cycles produced coatings that have denser microstructures, less texture, compressive stresses and increased lattice defects. • Duty cycle change was a powerful tool to achieve arc coatings with low defect density, high crystal quality and low stress.

Wear of AlCrN and CrAlSiN Coatings Applied to Nonstandard Involute Gears

Wear of nonstandard involute gears with two types of coatings, AlCrN and CrAlSiN, was studied. The coatings were applied by cathodic arc deposition. The gears were tested using a Niemann tester at a graduated load up to the 12th load stage and were compared to noncoated gears. Both Biogear S150 gear oil and PP90 universal hydraulic oil were applied during these tests. The thickness of deposited coatings and wear of gear teeth were studied by SEM and their chemical compositions were determined by EDS analysis. Maximal contact pressure of 1350 MPa was calculated in the region of the tooth flank at the 12th load stage. Maximal frictional stress was also calculated on the tooth flank. The resistance against wear of gears was evaluated based on the critical weight loss and mainly based on the critical surface roughness of gears. The critical roughness was exceeded at the 10th load stage for noncoated gears. For the gears with AlCrN and CrAlSiN coatings, the critical roughness was exceeded at the 11th load stage. Wear of AlCrN and CrAlSiN coatings was nonuniform along the height of tooth. Wear on the tooth flank was characterized by fragmentation of thin coatings and subsequent detaching of fragments from the steel substrate. The steel substrate was worn by microcutting, which caused the highest roughness on the tooth surface. On the tooth pitch, surface protrusions of coatings were smoothed, and coatings cracked and locally detached subsequently. On the tooth face, surface protrusions were also smoothed but coatings remained compact without crack initiations. Both experimental oils, Biogear S150 and PP90, proved to be suitable during Niemann tests as their temperatures did not exceed the limit value of 80 °C.

Enhancement of high temperature steam oxidation resistance of Zr–1Nb alloy with ZrO2/Cr bilayer coating

The ZrO2/Cr bilayer coating on Zr–1Nb alloy fabricated by plasma electrolytic oxidation and filtered cathodic vacuum arc deposition duplex treatments had good steam oxidation resistance. The mass gain of ZrO2/Cr-coated alloy was about 36 %, 44 % and 59 % of that of Cr-coated one after 3600 s steam oxidation at 900 °C, 1000 °C and 1100 °C, respectively. The top Cr layer for Cr-coated and ZrO2/Cr-coated alloys was oxidized into a Cr2O3 layer, and then a part of Cr2O3 was reduced by Zr to form metallic Cr layer again after the as-prepared Cr layer was completely consumed.

Correlation between Raman spectra and oxygen content in amorphous vanadium oxides

Amorphous vanadium oxide films were produced using a cathodic arc deposition technique. Varying oxygen pressure in a chamber during the film growth, we obtained the samples with different oxygen concentration. Elemental composition of our films was studied by Rutherford backscattering spectroscopy and energy dispersive X-ray analysis. Raman characterization of the samples showed the strong influence of oxide stoichiometry on the spectra: the main feature was attributed to stretching vibrations of vanadyl bonds and its position shifted from 879 to 937 cm−1 upon changing the V/O ratio from VO2 to V2O5. An explanation of such behavior and an empirical formula of this dependence were suggested.

Al–AlN composite coatings on AZ31 magnesium alloy for surface hardening and corrosion resistance

Al–AlN composite coatings were prepared using filtered cathodic vacuum arc deposition on AZ31 magnesium alloy substrates. With increasing substrate bias, AlN phase content increased and Al phase content decreased, resulting in increased hardness of the coatings. Transmission electron microscopy morphology of the composite coatings at 100 V bias showed that the metallic Al phase was embedded in the AlN matrix. The coatings significantly enhanced the corrosion resistance of the AZ31 magnesium alloy. The maximum hardness was 512 HV obtained at a bias of 300 V and a minimum corrosion current density was 1.913 × 10−6 A/cm2 attained at a bias of 100 V. The effect of substrate bias on microstructure, coating thickness, and residual stress in the coatings was studied in details.

Tailoring Crystalline Structure of Titanium Oxide Films for Optical Applications Using Non-Biased Filtered Cathodic Vacuum Arc Deposition at Room Temperature

Titanium oxide films were deposited at room temperature and with no applied bias using a filtered cathodic vacuum arc (FCVA) system in a reactive oxygen environment. The dependence of film growth on two process parameters, the working pressure (Pw) and the O2 partial pressure (pO2), is described in detail. The composition, morphological features, crystalline structure, and optical properties of the deposited films were systematically studied by Rutherford Back Scattering (RBS), Scanning Electron Microscopy (SEM), X-Ray diffraction (XRD), Raman Spectroscopy, UV-vis spectroscopy, and spectroscopic ellipsometry. This systematic investigation allowed the identification of three different groups or growth regimes according to the stoichiometry and the phase structure of the titanium oxide films. RBS analysis revealed that a wide range of TiOx stoichiometries (0.6 < × < 2.2) were obtained, including oxygen-deficient, stoichiometric TiO2 and oxygen-rich films. TiO, Ti2O3, rutile-type TiO2, and amorphous TiO2 phase structures could be achieved, as confirmed both by Raman and XRD. Therefore, the results showed a highly versatile approach, in which different titanium oxide stoichiometries and crystalline phases especially suited for diverse optical applications can be obtained by changing only two process parameters, in a process at room temperature and without applied bias. Of particular interest are crystalline rutile films with high density to be used in ultra-high reflectance metal-dielectric multilayered mirrors, and reduced-TiO2 rutile samples with absorption in the visible range as a very promising photocatalyst material.

Effects of silicon doping on low-friction and high-hardness diamond-like carbon coating via filtered cathodic vacuum arc deposition

In this study, silicon (Si) was doped on a tetrahedral amorphous carbon (ta-C) coating and the tribological characteristics of the resulting Si-doped diamond-like carbon (DLC; a-C:Si:H) were investigated against a SUJ2 ball. The Si fraction in the coating was varied from 0 to ~ 20 at.% by increasing the trimethylsilane gas flow rate during filtered cathodic vacuum arc deposition. The coefficient of friction (CoF) showed no obvious change when the Si fraction was less than ~ 7 at.%. However, after Si doping, it significantly decreased when the Si fraction was greater than ~ 8 at.%. The running-in period also decreased to less than 1000 cycles after Si doping. The rapid formation of Si-rich debris and transfer layer led to the fabrication of a low-friction tribofilm, which was induced by the tribochemical reaction with moisture under ambient conditions. When the Si fraction was ~ 17 at.%, the lowest CoF of less than 0.05 was obtained. Further Si doping beyond the critical point led to the destruction of the film because of reduced hardness.

Tribological properties of multilayer tetrahedral amorphous carbon coatings deposited by filtered cathodic vacuum arc deposition

Tetrahedral amorphous carbon (ta-C) has emerged as an excellent coating material for improving the reliability of application components under high normal loads. Herein, we present the results of our investigations regarding the mechanical and tribological properties of a 2-µm-thick multilayer ta-C coating on high-speed steel substrates. Multilayers composed of alternating soft and hard layers are fabricated using filtered a cathodic vacuum arc with alternating substrate bias voltages (0 and 100 V or 0 and 150 V). The thickness ratio is discovered to be 1:3 for the sp2-rich and sp3-rich layers. The results show that the hardness and elastic modulus of the multilayer ta-C coatings increase with the sp3 content of the hard layer. The hardness reached approximately 37 GPa, whereas an improved toughness and a higher adhesion strength (> 29 N) are obtained. The friction performance (µ = 0.07) of the multilayer coating is similar to that of the single layer ta-C thick coating, but the wear rate (0.13 × 10−6 mm3/(N·m)) improved under a high load of 30 N. We further demonstrate the importance of the multilayer structure in suppressing crack propagation and increasing the resistance to plastic deformation (H3/E2) ratio.

Corrosion performance and tribological behavior of diamond-like carbon based coating applied on Ni−Al−bronze alloy

The effect of diamond-like carbon (DLC) coating (fabricated by cathodic arc deposition) on mechanical properties, tribological behavior and corrosion performance of the Ni−Al−bronze (NAB) alloy was investigated. Nano-hardness and pin-on-plate test showed that DLC coating had a greater hardness compared with NAB alloy. Besides, the decrease in friction coefficient from 0.2 for NAB substrate to 0.13 for the DLC-coated sample was observed. Potentiodynamic polarization and EIS results showed that the corrosion current density decreased from 2.5 μA/cm 2 for bare NAB alloy to 0.14 μA/cm 2 for DLC-coated sample in 3.5 wt.% NaCl solution. Moreover, the charge transfer resistance at the substrate–electrolyte interface increased from 3.3 kΩ·cm 2 for NAB alloy to 120.8 kΩ·cm 2 for DLC-coated alloy, which indicated an increase in corrosion resistance due to the DLC coating.

Polarized Raman scattering in micrometer-sized crystals of triclinic vanadium dioxide

Triclinic vanadium dioxide VO2 (T) films were produced using cathodic arc deposition. Under certain conditions, the film growth on sapphire substrates Al2O3 (001) is associated with the formation of triclinic monocrystals with lateral sizes of several tens of micrometers. Borders between different crystallites can be determined by Raman mapping analysis. X-ray diffraction measurements revealed that the micrometer-sized monocrystals had two different orientations—epitaxial (002) and non-epitaxial (201). The film was studied by polarized micro-Raman spectroscopy, which can be used to determine the orientation of any single crystallite. The Raman tensor elements of the VO2 (T) phase were determined, and it was shown that though crystallographically triclinic VO2 cell could be fitted by monoclinic one with a high degree of precision, such monoclinic approximation was not valid in terms of Raman spectroscopy. Contrary to the two types of phonons expected for the monoclinic crystal [having five nonzero (four independent) or four nonzero (two independent) Raman tensor elements], all phonons in VO2 (T) have nine (six independent) generally nonzero tensor components.

Synthesis of Diamond-like Carbon as a Dielectric Platform for Graphene Field Effect Transistors

The platform for supporting two-dimensional (2D) materials such as graphene has a critical influence on the electronic properties of the materials it supports. Here we report on the filtered cathodic vacuum arc deposition (FCVAD) of atomically flat diamond-like carbon (DLC) films with varied C sp3/sp2 content ratio by modulating the parameters of substrate bias voltage, then used as a dielectric platform for supporting graphene. By doing this, an all-carbon DLC–graphene heterostructure would be formed. Through characterizing this heterostructure and constructing graphene field effect transistors (FETs) on DLC, it was shown that graphene on DLC platforms had less doping from the substrate and improved FET carrier mobility compared with that of graphene on SiO2/Si substrate. Moreover, the graphene on different DLC platforms exhibited an increased FET mobility (up to ∼7032 and 5558 cm–2 V–1 s–1 for hole and electron, respectively) with the increase of C sp3/sp2 bond fraction in DLC which could be tuned by the negative bias voltage applied to the deposited substrates in the FCVAD synthesis of DLC here.