Papers

ICMCTF2002 Session B1-2: PVD Hard Coatings and Technologies

Thursday, April 25, 2002 1:30 PM in Room Golden West

Thursday Afternoon

Start	Invited?	Item
1:30 PM		B1-2-1 Large Scale Synthesis of Fullerenes, Nanotubes and Bucky 'Onions' by Arc Discharge in Liquids M. Chhowalla, N. Sano (University of Cambridge, United Kingdom); Hao Wang (The Chinese University of Hong Kong, PR China); I. Alexandrou, GAJ Amaratunga (University of Cambridge, United Kingdom) Carbon nanotubes and fullerenes have extraordinary electrical and mechnical properties that make them ideal for numerous applications. However, for applications such as fuel cell electrodes and nano-composite structural materials, large quantities (kilograms) of the material are desired. The widely used methods to fabricate nano-materials require vacuum systems to generate plasmas using an arc discharge, laser ablation or glow discharge. These methods suffer in bulk production from not only the high investment and running costs of the vacuum equipment but also from low yield of the desired products. Furthermore, in addition to the desired nano-materials, the vacuum processes also yield unwanted contaminants (amorphous carbon and disordered nano-particles) so that a time consuming and costly purification step must be carried out. A simple method to fabricate high-quality spherical nano-materials in large quantities without the use of vacuum equipment is reported. The nano-particles are generated by an arc discharge between two electrodes submerged in water. Using this simple technique, we are able to generate spherical carbon onions with C₆₀ cores along with larger onion-like nested particles. In addition to carbon materials, we have also used this method to generate MoS₂ nano-particles. Our method requires only a dc power supply, carbon cathode and a consumable anode of the desired material and de-ionized water or liquid nitrogen. This method is outstandingly simple and economical compared to conventional techniques used to generate fullerenes and nanotubes.
1:50 PM		B1-2-2 Superhard nc-TiN/a-BN and nc-TiN/a-TiB_x/a-BN Coatings Prepared by Plasma CVD and PVD: A Comparative Study of their Properties P. Karvankova, M.G.J. Veprek-Heijman (Technical University Munich, Germany); O. Zindulka (SHM Ltd., Czech Republic); S. Veprek (Technical University Munich, Germany) We present a comparative study of the preparation and properties of superhard "Ti-B-N" coatings deposited by plasma CVD and by Vacuum Arc Evaporation (PVD) of Titanium combined with Plasma CVD of TiB₂ and BN. Using high frequency plasma CVD at a total pressure of several mbar with TiCl₄,l₃, N₂ and H₂ as reactants, superhard (H_v ? 40 – 50 GPa) nanocomposite coatings were successfully and reproducibly deposited and characterized in terms of mechanical properties (indentation & SEM), phase composition (XPS and ERD) and nanostructure (XRD, SEM). Using reactive sputtering several authors reported about the preparation of superhard TiN/TiB₂ coatings with only a small fraction of BN. Effort to increase the fraction of the BN phase resulted in soft films. In contrast, plasma CVD yields superhard nc-TiN/a-BN and nc-TiN/a-TiB₂/a-BN coatings in a wide range of the fractions of BN and TiB₂ phases. This is attributed to the high chemical activity of nitrogen under the conditions of plasma CVD. Industrial scale vacuum arc evaporation PVD in combination with plasma CVD is used for the large scale coating of machining tools by "Ti-B-N" coatings. In the system nc-TiN/a-TiB₂ with a minor fraction of the a-BN phase superhard coatings with a very low fraction of microparticles and resultant low surface roughness of R_m ? 0.15 µm were successfully prepared and tested under a variety of cutting conditions. The work on the deposition of nc-TiN/a-BN by this technique is in progress. In the presentation we shall compare the advantage and drawback of these techniques and the properties of the deposited coatings.
2:10 PM		B1-2-3 Internal Stress Induced by Interfacial Free Energy in PTFE/Al and PTFE/Ti Nanomultilayered Films E. Kusano, N. Kikuchi, K. Tsuda, H. Nanto, A. Kinbara (Kanazawa Institute of Technology, Japan) Polytetrafluoroethylene(PTFE) is a material with a low surface free energy of about 17mJ/m². When PTFE is coupled to a material with a high surface free energy, a high free energy at the interface between the two materials is thought to induce anomalous properties. This effect may become remarkable if the two materials are nano-multilayered because of a large interface/bulk volume ratio of the nano-multilayered material. In this paper, PTFE has been multilayered with Al or Ti (The surface energy of Al is about 900 mJ/m² and that of Ti is about 1700 mJ/m².) to reveal effects of interface free energy on internal stress and other mechanical properties. All of PTFE, Al and Ti layers were deposited by magnetron sputtering. A PTFE sheet was used as the target to deposit PTFE layers. Modulation period was changed from 6.6 to 200 nm. Total thickness of a multilayered film was 200nm (100 nm of PTFE plus 100 nm of Al or Ti). Strain within metal layers was evaluated by X-ray diffraction. Microhardness and Young's modulus of the films were analyzed by nanoindentation. Ratio of energies dissipated and loaded during a nanoindentation test was estimated from a load-displacement curve. Strains in the metal layers of PTFE/Al and PTFE/Ti increased from 0.1% to about 0.8% with decreasing modulation period. This means that internal stress in the metal layers increased with decreasing modulation period. Microhardness and Young's modulus of the multilayered films were found to increase with decreasing modulation period. The evaluation of the ratio of dissipated/loaded energy also exhibited that the film became more elastic with decreasing modulation period. It is concluded that an accumulated interface free energy induces strain in metal layers and make the multilayered films harder and more elastic.
2:30 PM		B1-2-4 Multifunctionality by Nanocrystalline Composite TiSiN Coatings F. Kauffmann, G. Dehm, E. Arzt (Max-Planck-Institute for Metals Research, Germany); V. Schier (Walter AG, Germany); S. Henke, A. Schattke, T. Beck (Robert Bosch GmbH, Germany) It is the aim of our project to produce single layer wear resistant coatings composed of nanocrystalline titanium nitride (nc-TiN) embedded in an amorphous silicon nitride (a-SiN_x) matrix. The nc-TiN/a-SiN_x coatings are expected to combine properties such as high hardness, high-temperature stability, toughness and a low friction coefficient. The coatings were prepared at low temperatures by physical vapour deposition techniques applicable to industrial production equipment. The microstructure of the deposited coatings was investigated by focused ion beam and transmission electron microscopy. The microscopy studies revealed a transition from a columnar TiN microstructure with {111}-texture to a nc-TiN microstructure with {200}-texture with increasing Si-content. High resolution transmission electron microscopy has been used to confirm a nc-TiN grain size of less than 10 nm in coatings with a silicon content of more than 5 at%. The hardness of the coatings, which was determined using nanoindentation, reaches values of about 45 GPa. This work is supported by the federal ministry of education and research (Bundesministerium für Bildung und Forschung) (contract number MaTech 03N3081). The authors are responsible for the content of this publication.
2:50 PM		B1-2-5 Structure and Mechanical Properties of Cr-Cu-based Nanocomposite Coatings Deposited by Magnetron Sputtering A. Leyland, C. Tsotsos, M.C Joseph, A.D. Wilson, A. Matthews (University of Hull, United Kingdom) Nanostructured Cr-Cu films with and without interstitial additions of elements (i.e. B, C and N) show great potential for producing hard yet tough tribological coatings with low elastic modulus (compared to ceramic coatings). This work examines the microstructural and tribological properties of coating systems based on the immiscible Cr-Cu binary metal system. Coatings were deposited on M2 tool steel and AISI 316 austenitic stainless steel coupons by reactive magnetron sputtering in a filament-enhanced dc unbalanced magnetron system. Coating microstructures were characterised using scanning electron microscopy (SEM) and glancing angle X-ray diffraction (XRD) analysis; composition analyses were carried out by means of glow-discharge optical emission spectroscopy (GDOES). Surface hardness and elastic moduli of the films were determined by Knoop microhardness and nanoindentation measurements. High frequency ball-on-plate impact and reciprocating sliding wear tests were used to correlate microstructure and composition to coating mechanical properties.
3:10 PM		B1-2-6 Stability of Quasicrystalline Phases for As-deposited AlCuFeCr PVD Coatings M.J. Daniels (University of Michigan, Ann Arbor); D. King (Technology Assessment and Transfer); J.S. Zabinski (Air Force Research Laboratory); J.C. Bilello (University of Michigan, Ann Arbor) Powder composite targets of AlCuFeCr were used to produce ~10 micron coatings by RF sputtering on a variety of substrates. Growth conditions used carrier gas pressures of 2.5 to 10 mTorr with various sample bias conditions. Previous reports on ternary AlCuFe and quaternary AlCuFeCr alloy sputtered films indicated that quasicrystalline coatings could not be produced in the as-depostied state. Instead, a supposedly amorphous state existed and subsequent annealing was necessary to produce the quasicrystalline microstructure via a phase transformation. In the present work the as-deposited coatings were studied using SEM, TEM and high-resolution grazing angle x-ray scattering at the Stanford Synchrotron Radiation laboratory. The results of these observations suggest that the as-deposited AlCuFeCr coatings produced microstructures that were principally extremely fine grained quasicrystalline plus approximant phases. The grain sizes were determined to be of the order of <10nm via a Scherrer line broadening analysis. For such small grain size distributions, ordinary laboratory x-ray sources would not be able to tell the difference between nanocrystalline and amorphous microstructures. Finally our observations showed that the as-deposited nanocyrstalline phases were extremely robust and could be produced for a wide variety of target compositions and sputter conditions. Acknowledgement: Thanks to the AFOSR, DARPA, and DoE for support of this project.
3:30 PM		B1-2-7 Atomic-Scale Surface Processes Controlling the Growth of Cubic Transition-metal Nitrides: TiN, CrN, ScN, and TaN D. Gall, C.-S. Shin, S. Kodambaka, M.A. Wall, I. Petrov, J.E. Greene (Frederick Seitz Materials Research Laboratory, University of Illinois) We have developed an atomistic understanding of NaCl-structure transition-metal nitride thin film growth based upon combined experimental and computational investigations, across many length-scales, of film microstructural and surface morphological evolution, surface island decay kinetics, and single atom processes. Polycrystalline and epitaxial layers of TiN, CrN, ScN, and TaN were grown on SiO₂ and MgO(001) at 450-1050 °C by ultra-high-vacuum magnetically-unbalanced magnetron sputter deposition in pure N₂ and N₂/Ar atmospheres. Polycrystalline layers grown under low ion-irradiation conditions exhibit a columnar microstructure with strong 111 preferred orientation which evolves through a kinetically-limited competitive growth mode. This is due to a large anisotropy in adatom mobilities and binding energies as shown by T-dependent STM nucleation length measurements and by ab-inito density functional calculations. Activation energies for surface diffusion on TiN are 0.8 and 1.7 eV for (001) and (111) surfaces, resulting in preferential 3D growth on 111 grains. However, the presence of atomic N on the growth surface, obtained by 20 eV N₂⁺ irradiation during deposition, dramatically reduces cation mobilities leading to a purely 001 texture. The high anisotropy in adatom mobilities gives rise to another unique microstructural feature: epitaxial 001-oriented layers exhibit self-organized arrays of 1-nm-wide nanopipes which are formed as a result of periodic kinetic surface roughening and subsequent atomic self-shadowing. While the microstructures of NaCl-structure TM-nitrides are similar, their physical properties vary widely. For example, TiN is metallic, ScN is semiconducting, and CrN is a Mott insulator. Measured hardnesses of single crystal 001-oriented layers are 20, 21, 28, and 31 GPa for TiN, ScN, CrN, and TaN, respectively.
4:10 PM		B1-2-9 Sputter Deposition of Crystalline Alumina Coatings R. Cremer, K. Reichert, D. Neuschütz (LTH, RWTH Aachen, Germany); G. Erkens, T. Leyendecker (CemeCon GmbH, Germany) In the last years a variety of plasma sources have been developed for film deposition by magnetron sputtering. In addition to RF and DC sputter sources, pulsed DC and low-frequency plasma sources are gaining increased attention in sputter technology. This interest is driven by the wish of depositing coatings with superior properties as compared to those deposited by conventional techniques. One prominent example of coatings that are significantly enhanced by the usage of pulsed sputter deposition is alumina. Although crystalline α-alumina can be deposited by thermal CVD at temperatures above 1000 °C for two decades, no process for the deposition of crystalline alumina at low temperatures is commercially available up to now. In this paper, the results of a detailed study of the plasma parameters during bipolar pulsed magnetron sputtering and their effect on the properties of alumina hard coatings is reported. Langmuir type voltage measurements at the substrate position, optical emission spectroscopy as well as mass spectroscopy were used to monitor the effect of target poisoning on the reactive deposition of alumina. Those principal observations were connected to easily available process parameters like discharge voltage and oxygen partial pressure. Based on these measurements, the deposition of crystalline γ-alumina with high hardness and good adhesion under technical conditions was achieved.
4:30 PM		B1-2-10 The Properties of Aluminum Oxide and Nitride Films Prepared by dc Sputter-deposition from Metallic Targets T.P. Drüsedau, T. Neubert, A.N. Panckow (Otto-von-Guericke Universität Magdeburg, Germany) Thin films of aluminum nitride and aluminum oxide were prepared at 540 K substrate temperature by dc-magnetron sputtering from a metallic Al-target in pure nitrogen and oxygen atmosphere, respectively. Characterization of the films was performed by x-ray diffraction, x-ray reflection and by optical transmission spectroscopy. The stoichiometric composition of the films was ascertained by XPS. As a function of reactive gas pressure, the deposition rate showed in general a logarithmic decrease with increasing pressure. Oxide films were deposited at about a fourth the rate of nitride films as consequence of the lower sputtering yield. For the oxide films, specific gravity and static refractive index showed weak changes with pressure and amounted to 2.7 g/cm³, which is only about 75 % of the bulk density, and 1.65, respectively. In contrast, low-pressure sputter-deposition of nitride films resulted in high-density films of about 95 % the bulk value and a refractive index close to 2.1. Nitride films show a strong (002) texture (c-axis orientation) with large nanograins up to 90 nm length. Oxide films are in general amorphous. The very different structure of nitride and oxide films is related to the more complicated crystal lattice of the oxide. The enhancement of the mobility of the adatoms by the moderate bombardment inherent to dc sputter-deposition is only sufficient only to grow dense films consisting of the relative uncomplicated hexagonal AlN crystals.