ICMCTF2011 Session B1-3: PVD Coatings and Technologies

In this paper, we present a preliminary study of Ti-Si-C-N nanocomposite coatings deposited on the inner surface of cylinders using a plasma enhanced magnetron sputtering (PEMS) technology. Wear, erosion, abrasion and corrosion may occur to the inner surface of cylinders of various industrial components including gun barrels, internal combustion engine cylinders for passenger cars and electromotives, and liners and valve seats of various pumps for petroleum/natural gas exploration and transmission or hydraulic engineering. In many cases, the damage is quite severe due to the heavy work load and, very often, the presence of sand and corrosive media. Although cost of the components is generally high, the cost to shut down the equipment for the replacement of the component is often much higher. To address these issues, we developed a cylindrical magnetron sputter deposition technology. Using this technology, steel cylinders of 100 mm in diameter by 300 mm tall were deposited with Ti-Si-C-N coatings to a thickness up to 60 µm were deposited aiming at heavy duty applications. These coatings were studied using SEM, EDS, and XRD, and the nanocomposite structure was found to contain crystalline TiN and TiCN in the amorphous SiCN matrix. The hardness of the coatings reached HV3300. Erosion testting was conducted at two incident angles of 30° and 90° using 50 µm alumina. The Ti-Si-C-N coatings significantly reduced erosion of the steel substrate. In this paper, we will discuss the magnetron design and the characteristics. We further present the detailed microstructural, mechanical and tribological properties of the coatings.

Arc deposited nanocomposite coatings such as Ti-Si-N are of great technological interest due to their very high hardness, high temperature stability and corrosion resistance. Such coatings (Ti-Si-N, Zr–Si–N, Ti–Al–Si–N and Ti–Al–V–Si–N) have recently been fabricated, by a vacuum arc deposition process, with a great deal of control over the resulting microstructure and properties [1]. In addition, similar nanocomposite structures can be achieved by combining Ti/Hf/Zr oxides with DLC to create hard, inert coatings that may be highly suitable for biomedical applications [2].

The examination of the structure of these nanocomposite materials is extremely challenging. Cross-sectional transmission electron microscopy (TEM) has been made considerably simpler through the use of focused ion beam (FIB) – based specimen preparation methods. However, due to the fine size scale of the crystalline phases (5-50nm), the overlap of grains in transmission electron microscope (TEM) specimens makes it impossible to study the interfaces between the crystals in order to determine whether secondary amorphous phases are present. Atom probe tomography is a technique that provides atomic-scale 3D maps showing the distribution of elements within a selected area of material. New FIB-based specimen preparation methods and the development of new laser-pulsing technology makes this method available to the examination of arc-deposited hard coatings.

This paper will include the results of a study of Ti-Si-N, in which no evidence was found for the presence of a Si-rich phase at the boundaries between the crystallites. We will discuss the challenges and limitations around the application of atom probe tomography in studying arc-deposited hard coatings.

[1] P. J. Martin , A. Bendavid , J. M. Cairney and M. Hoffman, Surf. Coat. Technol., [200], 2228 2005.
[2] L.K. Randeniya, A. Bendavid, P. Martin, J.M. Cairney, A. Sullivan, S. Webster, G. Proust, R. Rohanizadeh, Acta Biomaterialia , 6 (2010) 4154-4160 .

Various TiAlN based coatings are most commonly used composition for cutting tool application. Recently, more thermal stability and the higher film hardness are demanded because of the needs for dry cutting of harder work-pieces at higher cutting speed. Considering this circumstance, we have examined the effect of the Si addition on (Ti,Cr,Al)N films, and have developed an excellent film with high hardness and improved thermal stability. We have examined effect of Si content in (Ti,Cr,Al)N up to 5 at% [1]. In this report, further improvement of film characteristic was achieved by increasing the Si content more than 5 at%. Cutting performance of (Ti,Cr,Al,Si)N film with different Si compositions and the correlation with the film structure was investigated.

(Ti,Cr,Al,Si)N films with different Si content were deposited by a cathodic arc ion plating (AIP) equipment. Ti–Cr–Al–Si targets were prepared by powder metallurgy process and used for the deposition. Their compositions were Ti0.2-Cr0.2-Al0.55-Si0.05, Ti0.2-Cr0.2-Al0.52-Si0.08 and Ti0.3-Cr0.18-Al0.42-Si0.12. Deposition was conducted in the AIP coater in pure N2 atmosphere at a pressure of 4.0 Pa. WC-Co cutting inserts, platinum foils (0.1mmt) and WC-Co ball end-mills were used as substrates. The substrate bias during deposition was varied from 30 to 200 V to investigate the effect of substrate bias on film’s properties.

XRD analysis result shows that crystal structure of the (Ti,Cr,Al,Si)N films deposited with bias 30V has mixed structure with hexagonal phase (Wurzite structure) and cubic rock-salt structure (B1 phase), the films deposited with bias more than 65V has B1 cubic single phase regardless of the Si content. Indentation hardness is about 30 GPa for (Ti,Cr,Al,Si)N films with 8 % of Si although the indentation hardness of the 5% Si film is approximately 26 GPa. Additionally, by increasing the Si content, oxidation resistance was greatly improved. The formed oxide layer is about 1100 nm for 5% Si film after annealing in dry air at 1000˚C for 30 minute, while the oxide layer of oxides is approximately 400 nm for 8% Si film. The detailed relationship between the cutting characteristic and the film structure will be included in the presentation.

Piezoelectric aluminum nitride (AlN) thin films were deposited by reactive sputtering of Al metal target in nitrogen atmosphere using a pulsed closed field unbalanced magnetron sputtering system on various substrates using different seed layers such as Cr, Ti/TiN, Pt, Mo and Al. The texture, orientation and piezoelectric properties of AlN films were characterized by means of x-ray diffraction, field emission scanning electron microscopy and laser interferometry. A Michelson laser interferometer was designed to obtain the converse piezoelectric response of the deposited AlN thin films. It was found that the incorporation of different seed layers in the sandwiched structure, significantly affected the (002) orientation and the piezoelectric response of AlN thin films.

Industrial-scale synthesis of oxide coatings with tailored properties is of vital importance for bringing fundamental R&D small-scale research results into commercial applications and consumer products.

The Tribology Centre at Danish Technological Institute has performed large-scale reactive pulsed DC sputter deposition of TiO₂ and Cu-doped TiO₂ for photocatalytic and anti-microbial applications. In addition, cerium gadolinium oxides (CGO) and yttria stabilized zirconia (YSZ), and alternating layers hereof, have been synthesized for intermediate temperature solid oxide fuel cell applications. The various coatings were deposited on a commercial CemeCon CC800/Sinox unit.

For the TiO₂ system it will be shown that reproducible growth of dense as well as highly porous (featherlike) TiO₂ coatings can be synthesized in the rutile and the anatase crystal phase (or mixtures hereof) as evident from SEM and XRD results. It will be demonstrated that by carefully controlling the deposition temperature and the substrate bias voltage, nucleation and growth of the photocatalytic active anatase can be tailored. The photocatalytic activity has been quantified by oxidation of acetone into CO₂ and correlated to the obtained structure and film morphology, thicknesses and choice of substrate material (silicon, stainless steel, glass, aluminium and polycarbonate). The effect on the film structure and the photocatalytic activity upon doping with e.g. Cu and the impact on antimicrobial properties will be addressed.

For solid oxide fuel cell (SOFC) applications YSZ is frequently encountered as the electrolyte material. In order to reduce operating temperature of the SOFC, thin YSZ electrolyte coatings are of great interest. In this respect, it is of utmost importance to control the crystal structure and morphology of the deposited YSZ thin films – not only on ideal model substrates. To prevent strontium diffusion to the electrolyte from strontium-containing cathode materials, gadolinia-doped ceria (CGO) barrier layers can be applied.

YSZ and CGO single and multilayer thin films were synthesized by reactive pulsed DC magnetron sputtering from Zr_0.84Y_0.16 and Ce_0.9Gd_0.1 targets, respectively. Crystal structure and morphology were investigated by XRD, TEM and SEM analysis showing that dense films could be grown with a cubic fluorite crystal structure. The grain size and texture of both YSZ and CGO films could be controlled through substrate bias and temperature variations. When depositing multilayers of CGO and YSZ, significant template effects could be identified, i.e. local epitaxial growth was observed.

Antibacterial activity of TiO₂ thin films prepared by Cathodic Arc Evaporation-Physical Vapour Deposition (CAE-PVD) was studied with respect to E. Coli and S. Aureus in UV radiation conditions. TiO₂ thin films were deposited on stainless steel (AISI 304) and commercial ceramic samples. The effect of doping TiO₂ has been analyzed; silver and nitrogen ions have been tested as dopants. Silver was added by a coevaporation process during the TiO₂ deposition process, while nitrogen ions were implanted using a WHICKHAM IBS 200 ion implantation equipment. A specific UV lamp emitting at 360-390 nm wavelength (OSRAM L36W/76) has been utilized to activate the photocatalytic response of the titanium oxide surface in contact with the bacteria.

The characterization of the coatings includes FE-SEM, AFM and Contact Angle analyses, moreover, a complete study of the mechanical properties of the TiO₂ thin films have been performed, including adhesion analyses (scratch test) and nanoindentation measurements.

Artificial superlattices consisting of multiferroic BiFeO₃ (BFO) and conductive LaNiO₃ (LNO) were epitaxial grown on Nb-doped SrTiO₃ (001) single crystal substrate at temperatures in a range of 560–810°C by a RF magnetron sputtering system. X-ray reflectivity and high-resolution diffraction measurements were employed to characterize the microstructure of these films. The formation of a superlattice structure was confirmed from the appearance of Bragg peaks separated by Kiessig fringes in x-ray reflectivity curve and a diffraction pattern. The clearly discernible main feature and satellite features on both sides of the substrate about the (002) SrTiO₃ Bragg peak indicate the high quality of the BFO/LNO artificial superlattice structure formed on a SrTiO₃ substrate at all temperatures of deposition.

X-ray measurements show that these superlattice films become subject to greater tensile stress along the c-axis, increased compressive stress parallel to the surface plane and increased crystalline quality with increasing the temperature of deposition except for the film deposited at ≧ 750℃.

Zinc oxide (ZnO) is a semiconducting, photoconducting, piezoelectric and optical waveguide material that shows a wide range of scientific and technological applications. ZnO thin films can be grown (or synthesized) by a variety of deposition techniques, such as sol-gel process, pulsed laser deposition, molecular beam deposition, chemical vapour deposition, sputtering, etc. The most commonly used technique is sputtering, and more concretely, non-reactive RF magnetron sputtering because of the good quality of the films obtained. In this work, we have used room temperature DC reactive magnetron sputtering at different oxygen partial pressures for the deposition of the films. In this way we have performed a systematic study of the stoichiometry and the related changes in the texture and the optical properties of the coatings. In addition, the effect of post deposition annealing treatments on the structure and electrical performance has been investigated. The chemical composition has been assessed by Rutherford Backscattering Spectroscopy (RBS) and Infrared absorption spectroscopy (IR) . The structural, morphologic and topographic changes have been characterized by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM). In selected samples we have completed the analysis of the bonding structure and phase composition by x-ray absorption near edge structure (XANES) using synchrotron radiation. Finally, the optical (transmittance in the visible region, band-gap, refractive index and UV emission) and electrical properties (resistivity) have been assessed by UV-Vis spectroscopy, Spectroscopic ellipsometry (SE) and four-point probe measurements.