Cathodic Arc Deposition Research Articles

Properties of carbon coatings obtained by pulsed high power methods of vacuum-arc and magnetron sputtering

Investigation results of the structure, mechanical, tribological and adhesion characteristics of carbon coatings obtained by two different methods: high-power impulse magnetron sputtering (HiPIMS) and pulsed cathodic arc deposition (PCAD) are presented. Coatings obtained by PCAD demonstrated higher hardness and tribological characteristics, but lower adhesion and higher internal stresses. The defectiveness of coatings deposited by both methods is almost the same

Tribo-corrosion performance of filtered-arc-deposited tantalum coatings on Ti-13Nb-13Zr alloy for bio-implants applications

Tantalum coatings were deposited on Ti-13Nb-13Zr alloy by filtered cathodic vacuum arc deposition in order to improve the alloy's wear and corrosion resistance under load-bearing, biomedical applications. The Ta coating exhibits an amorphous structure, which transforms into a mixture of alpha and beta phases as the substrate is heated to 300°C during deposition. Tribo-corrosion tests were performed using a ball-on-disk tribometer under simulated joint fluid at 37°C by sliding the uncoated and Ta-coated surfaces against alumina balls. The Ta coatings showed a significant reduction in the coefficient of friction under these test conditions. The wear rates of the Ta-coated disk surfaces are slightly lower than those of the bare Ti-13Nb-13Zr alloy, while the wear rate of the alumina balls was one order of magnitude higher when it slid against the Ta-coated samples than when it was slid against the Ti-13Nb-13Zr alloy. The wear debris generated from the Ta-coated samples sliding against alumina was comparatively smaller than that generated by the uncoated alloy against alumina. The wear characteristics of the Ta coatings do not favour using such coatings on implant materials. The Ta coatings exhibited a strong capacitive response which is proposed to enhance corrosion protection of the Ti-13Nb-13Zr alloy.

Design of high-temperature solar-selective coatings based on aluminium titanium oxynitrides AlyTi1−y(OxN1−x). Part 1: Advanced microstructural characterization and optical simulation

Aluminium titanium oxynitrides were studied as candidate materials for high temperature absorbers in solar selective coatings due to their excellent stability and their tuneable optical behaviour. A set of individual AlyTi1−y(OxN1−x) layers with different oxygen content was prepared by cathodic vacuum arc (CVA) deposition. The composition, morphology, phase structure and microstructure of the films were characterized by elastic recoil detection (ERD), scanning and transmission electron microscopy and X-ray diffraction. An fcc phase structure is found in a broad compositional range of AlyTi1−y(OxN1−x). Simultaneously, sample microstructure and morphology undergo systematic changes from a columnar growth to the development of a heterogeneous structure with spherical nanoparticle inclusions when the oxygen concentration is increased. The optical properties were determined by spectroscopic ellipsometry and UV–Vis–NIR and FTIR spectrophotometry. A comprehensive analysis of the film properties allowed an accurate modelling of the optical constants of the AlyTi1−y(OxN1−x) in the whole wavelength range of solar interest (from 190nm to 25µm). It points to a transition from metallic to dielectric behaviour with increasing oxygen content. Consequently, it is demonstrated that the optical properties of these AlyTi1−y(OxN1−x) deposited films can be controlled in a wide range from metallic to dielectric character by adjusting the oxygen concentration, opening a huge range of possibilities for the design of solar selective coatings (SSC) based on this material. Complete SSC, including a TiN layer as IR reflector, were designed by applying optical simulations, obtaining excellent optical selective properties of α = 94.0% and εRT = 4.8%.

Mechanical and tribological behavior of Ti/TiN and TiAl/TiAlN coated austempered ductile iron

Bilayer Ti/TiN and TiAl/TiAlN coatings were deposited onto austempered ductile iron (ADI) substrates by cathodic arc deposition in an industrial device. Structure and mechanical properties of the coated samples were comparatively examined. Wear behavior of the coated samples was investigated in comparison with uncoated ADI by means of rolling contact fatigue (RCF) tests, performed in a flat washer type testing rig and using lubricated pure rolling conditions. RCF tests results were analyzed using the two-parameter Weibull distribution and the Weibayes method.The results indicate that TiN and TiAlN coatings grew with a cubic-NaCl type structure. The arithmetic average roughness of the coated samples is similar for both coating variants. The surface hardness and residual stresses are higher for the TiAl/TiAlN coated samples. The coating hardness and elastic modulus are also higher for TiAl/TIAlN. The critical loads at massive delamination and the evolution of the friction coefficients are quite similar for both coating variants. Regarding RCF, failures in coated samples were characterized by substrate spalling. No massive delamination was observed in Ti/TiN and TiAl/TiAlN coatings. The statistical analysis indicates that the deposition of Ti/TiN improves noticeably the RCF resistance of ADI while the deposition of TiAl/TiAlN does not produce significant changes. The properties mismatch between substrate and coating seems to play an important role in the RCF behavior of coated samples, since Ti/TiN coatings possess a lower mismatch with respect to ADI substrates as compared to TiAl/TiAlN.

Cathodic Arc Deposited CrAlSiN Coatings by Pulsed Current Input

Cathodic arc deposition technique is one of the green processes of the physical vapor deposition (PVD) systems. In this study, Cr and CrAlSi dual metal targets were used in order to synthesize CrAlSiN coatings. By using the cathodic arc pulsed current techniques, three different settings of pulsed current duty cycles were used. The microstructure of the coatings observed by XRD analysis shows all the coatings are B1-Rock salt structure with diffraction peaks of (111) and (200). The pulsed current input as compared to the constant current had presented the higher hardness up HV3771. Corrosion test by polarization method shows the best corrosion resistance of the CrAlSiN was achieved by pulsed current input at high cycle time.

The novel toxic free titanium-based amorphous alloy for biomedical application

Ti based amorphous alloy exhibits excellent properties for biomedical applications. In general, it has high strength, low elastic modulus, good corrosion resistance and satisfactory biocompatibility. This work reported on a systematic study of a novel Ti44Zr10Pd10Cu6Co23Ta7, Ti44Zr10Pd10Cu10Co19Ta7 and Ti44Zr10Pd10Cu14Co15Ta7 metallic glass. Cylindrical rod samples with diameter of 5mm and 20mm length were fabricated by induction melting and casting into copper mold. The cast rod was then used as plasma cathode in filtered cathodic vacuum arc (FCVA) deposition chamber. The Ti-based metallic glass (MG) thin film was produced and tested for subsequent cell culture investigation to understand the biocompatibility nature of the new alloy. X-ray photoelectron spectrometry (XPS) was employed to characterize the surface chemistry. The Ti–6Al–4V alloy was studied in parallel as a control material. This novel Ti-based MG composition has shown promising osteoblast biocompatible characteristics and no cytotoxicity on human osteoblast-like cells (SaOS-2). Moreover, cells on Ti-based MG thin film exhibited greater levels of calcium deposition using Alizarin red staining technique to those of the control. All results point out that the novel Ti-based amorphous alloy has potential for using as a new coating for biomedical application and deserve further study.

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.

Microstructure and Tribological Behavior of Stripe Patterned TiN Film Prepared with Filtered Cathodic Vacuum Arc Deposition (FCVAD)

This paper describes an experimental investigation into the influence of the stripe interspace and applied load on the tribological behavior of stripe patterned TiN films. The stripe patterned TiN films are deposited on an H13 steel surface by masked deposition with the filtered cathodic vacuum arc discharge (FCVAD) technique. The surface micro morphology, chemical composition, crystal structure, and mechanical properties of the films is characterized using 3D white light interferometry, scanning electron microscopy (SEM), X‐ray diffractometry (XRD), and a nano‐indentation tester, respectively. The tribological performance of patterned TiN is measured using a UMT‐5 tribometer, and the friction and wear mechanisms are analyzed, compared with that of the full TiN film and H13 steel substrate. The results show that the stripe patterned TiN films has better tribological properties than the full TiN film. These results are attributed to the synergistic effect between the surface pattern and the TiN film. The stripe interspace and the applied load has a more significant effect on the wear rate of the stripe patterned TiN films than the coefficient of friction of their friction pairs. A further study, however, is needed to analyze the relationship between the applied load and the wear rates of the stripe patterned TiN films.

Research on unusual cathode erosion patterns in the process of filtered cathodic vacuum arc deposition

The cathode spot is crucial to vacuum arc technology and the cathode spot theories have been widely studied. However, the study on a type of unusual erosion patterns is still very rare so far. For blocking this erosion patterns’ formation, a new cathode water cooling system with higher cooling efficiency was designed. The paper studies the formation of this erosion patterns by macro-particle filtered vacuum arc plasma, arc spots splitting, and arc spots movement velocity in pure argon gas and mixture gas (oxygen and argon). The ratio of oxygen to argon is from 0 to 2.5. Meanwhile, energy dispersive spectrometer (EDS) experiment was completed on the cross-section of this erosion pattern to study on the oxygen and other trace elements’ redistribution. In addition, an erosion model was proposed to explain the format process of these etching patterns. The results of this paper make a contribution to the theory of arc etching.

Effects of nitrogen vacancies on phase stability and mechanical properties of arc deposited (Ti0.52Al0.48)Ny (y < 1) coatings

Nitrogen sub-stoichiometric (Ti0.52Al0.48)Ny (0.92≥y≥0.46) coatings were grown in a mixed Ar/N2 atmosphere by cathodic arc deposition on cemented carbide (WC/Co-based) substrates. The coatings present a columnar structure with decreasing column widths from 250 to 60nm, due to a corresponding reduced N content, accompanied by changes in preferred orientation from 200 to 111 to 220. Among these, coatings prepared with 0.92≥y≥0.75 exhibit spinodal decomposition and consequently age hardening at elevated temperatures. A reduced N content upshifts the hardness maximum by >300°C. For these samples, the high temperature treatment resulted in interdiffusion of substrate elements, Co and C, mainly along column boundaries. Nevertheless, no detrimental effect in the hardness could be correlated. Conversely, a low N content sample (y=0.46) presents significant lattice diffusion of substrate elements Co, C, W, and Ta in the coating. In this case, the substrate elements are present throughout the coating, forming additional phases such as c-Ti(C,N), c-Co(Al,Ti,W), and c-(Ti,W,Ta)(C,N), with an observed increased hardness from 16 to 25GPa. We suggest that the substitution of nitrogen by carbon and the solution of W and Ta in c-TiN are responsible for the observed hardening. Our investigation shows the potential of sub-stoichiometric (Ti1−xAlx)Ny coatings for high temperature applications such as cutting tools and puts forth corresponding criteria for N content selection.

Hybrid Ti-MoS2 Coatings for Dry Machining of Aluminium Alloys

Combinatorial deposition, comprising filtered cathodic vacuum arc (FCVA) and physical vapor deposition (PVD) magnetron sputtering is employed to deposit molybdenum disulphide (MoS2) and titanium (Ti) thin films onto TiB2-coated tool inserts specifically designed for the dry machining of aluminium alloys. Titanium is deposited by FCVA while MoS2 is magnetron sputtered. The deposition set up allows several compositions of Ti-MoS2 to be deposited simultaneously, with Ti content ranging between 5 and 96 at. %, and their machining performances to be evaluated. Milling took place using a CNC Vertical Machining Center at a 877 mm/min feed rate. The effect of different coating compositional ratios on the degree of aluminium sticking when a milling insert is used to face mill an Al alloy (SAE 6061) was investigated using a combination of energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analysis. XPS studies suggest that the greater degree of Al sticking on the rake face of the inserts is due to the formation of greater amounts of non-protective Ti-O phases. EDX mapping of the milling inserts after machining reveal that a Ti:MoS2 ratio of around 0.39 prevents Al from sticking to the tool edges. Since we prevent Al from sticking to the tool surface, the resultant machined surface finish is improved thus validating the machining performance of TiB2-coated tools using optimum compositions of Ti:MoS2 thin film coatings.

Enhanced thermal stability and mechanical properties of nitrogen deficient titanium aluminum nitride (Ti0.54Al0.46Ny) thin films by tuning the applied negative bias voltage

Aspects on the phase stability and mechanical properties of nitrogen deficient (Ti0.54Al0.46)Ny alloys were investigated. Solid solution alloys of (Ti,Al)N were grown by cathodic arc deposition. The kinetic energy of the impinging ions was altered by varying the substrate bias voltage from −30 V to −80 V. Films deposited with a high bias value of −80 V showed larger lattice parameter, finer columnar structure, and higher compressive residual stress resulting in higher hardness than films biased at −30 V when comparing their as-deposited states. At elevated temperatures, the presence of nitrogen vacancies and point defects (anti-sites and self-interstitials generated by the ion-bombardment during coating deposition) in (Ti0.54Al0.46)N0.87 influence the driving force for phase separation. Highly biased nitrogen deficient films have point defects with higher stability during annealing, which cause a delay of the release of the stored lattice strain energy and then accelerates the decomposition tendencies to thermodynamically stable c-TiN and w-AlN. Low biased nitrogen deficient films have retarded phase transformation to w-AlN, which results in the prolongment of age hardening effect up to 1100 °C, i.e., the highest reported temperature for Ti-Al-N material system. Our study points out the role of vacancies and point defects in engineering thin films with enhanced thermal stability and mechanical properties for high temperature hard coating applications.

Ion induced stress relaxation in dense sputter-deposited DLC thin films

Deposition of high-density and low-stress hydrogen-free diamond like carbon (DLC) thin films is demonstrated using a pulsed ionized sputtering process. This process is based on high power impulse magnetron sputtering, and high C ionization is achieved using Ne as the sputtering gas. The intrinsic compressive stress and its evolution with respect to ion energy and ion flux are explained in terms of the compressive stress based subplantation model for DLC growth by Davis. The highest mass density was ∼2.7 g/cm3, and the compressive stresses did not exceed ∼2.5 GPa. The resulting film stresses are substantially lower than those achieved for the films exhibiting similar mass densities grown by filtered cathodic vacuum arc and pulsed laser deposition methods. This unique combination of high mass density and low compressive stress is attributed to the ion induced stress relaxation during the pulse-off time which corresponds to the post thermal spike relaxation timescales. We therefore propose that the temporal ion flux variations determine the magnitude of the compressive stress observed in our films.

Structural Characteristics of Diamond-Like Carbon Films Synthesized by Different Methods

In the present study, the Raman spectra of diamond-like amorphous (a-C) and hydrogenated amorphous (a-C:H) carbon films on silicon obtained using the ion-beam methods and the pulse cathodic arc deposition technique were investigated with the aim of elucidating the relation between the hardness and structure of the films. The hardness of the samples used in the present study was 19 – 45 GPa. Hydrogenated carbon films were synthesized using END–Hall ion sources and a linear anode layer ion source (LIS) on single-crystal silicon substrates. The gas precursors were CH4 and C3H8, and the rate of the gas flow fed into the ion source was 4.4 to 10 sccm. The ion energies ranged from 150 to 600 eV. a-C films were deposited onto Si substrates using the pulse cathodic arc deposition technique. The films obtained by the pulse arc technique contained elements with an ordered structure. In the films synthesized using low- (150 eV) and high-energy (600 eV) ions beams, an amorphous phase was the major phase. The significant blurriness of the diffraction rings in the electron diffraction patterns due to a large film thickness (180 – 250 nm) did not allow distinctly observing the signals from the elements with an ordered structure against the background of an amorphous phase.

Morphology and microstructure evolution of Ti-50 at.% Al cathodes during cathodic arc deposition of Ti-Al-N coatings

Today's research on the cathodic arc deposition technique and coatings therefrom primarily focuses on the effects of, e.g., nitrogen partial pressure, growth temperature, and substrate bias. Detailed studies on the morphology and structure of the starting material—the cathode—during film growth and its influence on coating properties at different process conditions are rare. This work aims to study the evolution of the converted layer, its morphology, and microstructure, as a function of the cathode material grain size during deposition of Ti-Al-N coatings. The coatings were reactively grown in pure N2 discharges from powder metallurgically manufactured Ti-50 at.% Al cathodes with grain size distribution averages close to 1800, 100, 50, and 10 μm, respectively, and characterized with respect to microstructure, composition, and mechanical properties. The results indicate that for the cathode of 1800 μm grain size the disparity in the work function among parent phases plays a dominant role in the pronounced erosion of Al, which yields the coatings rich in macro-particles and of high Al content. We further observed that a reduction in the grain size of Ti-50 at.% Al cathodes to 10 μm provides favorable conditions for self-sustaining reactions between Ti and Al phases upon arcing to form γ phase. The combination of self-sustaining reaction and the arc process not only result in the formation of hole-like and sub-hole features on the converted layer but also generate coatings of high Al content and laden with macro-particles.

Exploring the high entropy alloy concept in (AlTiVNbCr)N

We have explored the high entropy alloy (HEA) concept in the AlTiVNbCr-nitride material system. (AlTiVNbCr)N coatings synthesized by reactive cathodic arc deposition are close to an ideal cubic solid solution with a positive mean-field enthalpy of mixing of 0.06eV/atom. First principle calculations show a higher thermodynamic stability for the solid solution relative to their binaries thereby indicating a possible entropy stabilization at a temperature above 727°C. However, the elevated temperature annealing experiments show that the solid solution decomposes to w-AlN and c-(TiVNbCr)N. The limited thermal stability of the solid solution is investigated in relation to several thermodynamic parameters. We suggest that the HEA designed multiprincipal element (AlTiVNbCr)N solid solutions are in a metastable state.

Structure and corrosion properties of Cr coating deposited on aerospace bearing steel

The corrosion protection of chromium coating deposited on aerospace bearing steels by using the Filtered Cathodic Vacuum Arc deposition- Metal Evaporation Vacuum Arc duplex technique (MEVVA-FCVA) had been investigated. The protection efficiency of chromium coating on different substrate materials had also been evaluated. The chromium coating was mainly composed of nanocrystallineα-Cr in a range of 50–200nm. The orientation distributions of α-Cr film on substrates with different composition had a certain difference to each other. Electrochemical experimental results indicated that the chromium coating significantly improved the corrosion resistance of experimental bearing steels in 3.5% NaCl solution. The protective efficiency of chromium films were all over 98%. The corrosion resistance of chromium coating was influenced by the chemical composition of substrate material. The chromium coatings on higher Cr-containing substrate displayed lower corrosion current density and more positive corrosion potential. The increase of passive film thickness and the formation of a mass of chromium oxide and hydroxide on the surface are responsible for the improved corrosion properties.

Ultra low nanowear in novel chromium/amorphous chromium carbide nanocomposite films

In this work, we report the first observation of novel nanocomposite thin films consisting of nanocrystalline chromium embedded in an amorphous chromium carbide matrix (nc-Cr/a-CrC) with relatively high hardness (∼22,3GPa) and ultra low nanowear.The films were deposited onto silicon substrates using a magnetic filtered cathodic arc deposition system at various negative bias voltages, from 50 to 450V. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) suggested the co-existence of chromium and chromium carbide phases, while high resolution transmission electron microscopy (HRTEM) confirmed the presence of the nc-Cr/a-CrC structure. The friction coefficient measured with the ball-on disk technique and the nanowear results showed a strong correlation between the macro and nano-tribological properties of the samples. These novel nanocomposite films show promising properties as solid lubricant and wear resistant coatings with relatively high hardness, low friction coefficient and ultra low nanowear.

Corrosion behaviour and microstructure of tantalum film on Ti6Al4V substrate by filtered cathodic vacuum arc deposition

Tantalum (Ta) films of about 100nm in thickness were fabricated onto Ti6Al4V substrate using a filtered cathodic vacuum arc deposition system with and without a −100V bias between the substrate and the chamber wall. The structure of the deposited film at zero substrate bias exhibits pure tetragonal phase (beta-Ta), and body-centred cubic structure (alpha-Ta) is found as the substrate bias increased to −100V. The film deposited at −100V bias shows a significant improvement in cohesion as compared to the film deposited without substrate bias. Potentiodynamic polarization and electrochemical impedance tests in phosphate buffered saline solution revealed that the Ta film at −100V bias shows good corrosion resistance with a low corrosion current density of 0.009μA·cm−2. The film shows hydrophobic characteristics, low surface free energy and an inert surface presenting a uniform oxide layer, which is promising for potential biomedical implant applications.

Influence of surface preparation on the tool life of cathodic arc PVD coated twist drills

Cutting tool micro-geometry and surface integrity have been critical aspects to be considered for successful application of PVD thin films for cutting tool life enhancement. The present study examines in detail the role of pre-coating surface preparation (micro-blasting and drag finishing) on the tool life of coated cutting tools. TiN coating was deposited on different kinds of pre-treated (Micro blasting, Edge rounding and a combination of both) HSS and WC drills using cylindrical cathodic arc deposition method. They were subsequently characterized for surface roughness (Ra), adhesion strength and machining performance on EN 24 material. Pre-coating surface roughness (developed due to pretreatment) has a major influence on the adhesion strength of the coating. A lower pre-coating surface roughness with optimized edge rounding led to higher adhesion and edge strength which in turn resulted in a notable increase in tool life. Further underlining the importance of the present study, commercial TiN coatings deposited on HSS substrates were tested. The tool life obtained in the current study prolonged the tool life by a factor of 3 in comparison to the commercially available tools in the present day market.