ICMCTF2003 Session B8-3: Hard and Multifunctional Nano-structured Coatings

Tuesday, April 29, 2003 8:30 AM in Room Golden West

Tuesday Morning

Start	Invited?	Item
8:30 AM		B8-3-1 Multilayer Structural Analysis and Control of Hard Pvd Coatings using Grazing Angle X-ray Reflection Method H. Sun, S. Yang, H. Hruby, D.G. Teer (Teer Coatings Ltd, United Kingdom) Superlattice hard PVD coatings exhibit excellent properties such as high hardness and wear resistance, which depending on the choice of the coating material involved. The Closed Field Unbalanced Magnetron Sputtering Ion Planting Systems (CFUBMSIP) can easily produce and control the multilayer structure with up to four different material repeating layers. In this paper, wide angle X-ray diffraction method is used to analysis the coating structure, and grazing angle X-ray reflection method is used to measure and monitor the period of multilayer structure using a Philip X-ray Diffractometer. It is shown that this method can provide information on the different layers. Studies of two, three and four repeating layers are indicated that the coating properties can be strongly influenced by the multilayer period, λ, which is controlled by the coating parameters such as power supplied to magnetron targets, sample rotation speed and the distance between the sample and the magnetron targets. The hardness and wear properties of coatings are correlated with their multilayer period.
8:50 AM		B8-3-2 PACVD TiN/Ti-B-N Multilayers: from Micro- to Nano-scale M. Stoiber, S.M. Perlot (Materials Center Leoben, Austria); C. Mitterer (University of Leoben, Austria); C. Lugmair, R. Kullmer (Rübig, Austria) Multilayer coatings with nanometer sized layer arrangements such as superlattices exhibit many new structural as well as functional features and improved mechanical properties. Various physical vapor deposition methods have already been utilized to deposit superlattice coatings, while chemical vapor deposition is not suitable due to interdiffusion at high deposition temperatures. Therefore, the aim of this work was to investigate the potential of plasma-assisted chemical vapor deposition (PACVD) for multilayers with extension to the nanometer range. TiN/Ti-B-N multilayers have been deposited in an industrially sized deposition chamber to optimize mechanical and tribological properties. Different layer numbers (4, 8, 16, 32, 64, 128 and 300) of TiN and Ti-B-N (containing 23 as well as 52 at.-% B) have been alternately deposited by varying gas flow rates resulting in a total layer thickness of 2-3 µm. Electron energy loss spectroscopy (EELS) measurements showed separated 15 nm thick layers for a total of 128 layers. Coatings were deposited with and without intermediate sputtering between the individual layers enabling adjustment of biaxial stresses. A decrease in compressive stress has been observed for a decreasing individual layer thickness, which enhanced coating adhesion on tool steel. Hardness measurements were performed with a depth-sensing microhardness tester. Tribological properties were evaluated using a ball-on-disc tribometer and a microscale abrasion tester. For 4 layers the friction behavior is determined by the higher chlorine containing low-friction TiN layer resulting in a constant steady-state friction coefficient of 0.2 whereas stable values of about 0.8 were reached for higher layer numbers. The optimum wear resistance was obtained for 128 layers, which is attributed to well-defined interfaces and moderate compressive stresses. .
9:10 AM	Invited	B8-3-3 Lateral Rotating ARC-Cathodes: A New Technology for the Deposition of Advanced Nanocomposite Coatings M. Morstein, O. Coddet, T. Cselle (Platit AG, Switzerland); M. Jílek, P. Holubár (Pivot a.s., Novy Malín, Czech Republic); A. Karimi (Swiss Federal Institute of Technology (EPFL), Switzerland) (Ti,Al)N-based hard coatings dominate the market in high-performance cutting. The leading equipment manufacturers have maximized the aluminum share in order to improve film hardness, wear and heat resistance. Still, beyond 75 at.-% Al, a further increase is not useful. The nanocomposite concept provides a way to break through this dilemma: Embedding nano-crystalline Ti_xAl_1-xN grains in an amorphous Si₃N₄ matrix enables a structure of extremely high hardness (~47-50 GPa) maintained to very high temperatures (up to ~1100°C), even at lower Al contents of e.g. 50%. Highly ionized plasma is the key to successful cathodic arc deposition of nanocomposites. Today's state-of-the-art industrial PVD units, based on static planar cathodes, limit the maximum useable magnetic field intensity because of the danger of catastrophic target erosion. Dynamic lateral rotating arc cathodes (LARC^(R)) break through this dilemma: Strong magnetic fields are used to provide a highly ionized plasma without the danger of cutting into the electrode. Thanks to the fast, well-controlled motion of the arc track on the specially shaped cylindrical target, uniform evaporation even of low-melting materials is possible. Target poisoning can be controlled to a so far unmatched extent, and, using Al or Al-Si alloys as targets, advanced coatings can be now deposited within a wide compositional range without cathode changing. Turning the magnetic field creates a VIRTUAL SHUTTER^(R) free of any sensitive mechanical elements. Prior to deposition, the targets are cleaned to the backside, thus avoiding substrate contamination and ensuring optimum adhesion. Results will be presented on the microstructure and nanomechanical properties of the Platit AlTiSiN nanocomposite coatings. Tests of cutting tool performance will illustrate the potential of this new coating generation in conventional as well as extreme environments.
9:50 AM		B8-3-5 Mechanisms of Toughness Enhancement in Crystalline/Amorphous Nanocomposites A.A. Voevodin (Air Force Research Laboratory); C.D. Smith, I. Robertson, I. Petrov (University of Illinois); J.S. Zabinski (Air Force Research Laboratory, WPAFB) Designs of crystalline/amorphous nanocomposite hard coatings provide unique mechanical characteristics, such as a combination of a high hardness and toughness. Preliminary studies suggested possible mechanisms by which nanocomposite chemistry and structure caused increased toughness and maintained hardness. It is speculated that nanocrystalline inclusions prohibit dislocation activity, while nanometer sized amorphous regions between particles limit crack size. In this report, we correlate macroscopic mechanical tests of TiC/DLC crystalline/amorphous nanocomposites with direct microscopic observations of crack propagation using in-situ TEM straining stage experiments, developed at the University of Illinois. In-situ experiments showed crack initiation, propagation, branching, and termination in TiC/DLC nanocomposites (composed of 5-10 nm TiC grains separated by about 5 nm of the DLC matrix). To our knowledge, this is the first evidence that cracks propagate in the amorphous phase, passing around the nanometer sized TiC inclusions. This facilitates nano-grain shifts with respect to one another and results in macroscopic ductility of the 30 GPa hard TiC/DLC composite. TEM studies are correlated with the composite scratch, indentation, and sliding wear testing and comprehensive structure/chemistry analyses. Examples of a similar toughness enhancement in other material systems (WC/DLC and YSZ/Au) are provided.
10:30 AM		B8-3-7 The Role of the Substrate Bias on the Properties of Nanocomposite nc-TiC/a-C:H Thin Films T. Zehnder, J. Patscheider (EMPA, Switzerland) Thin nanocomposite films of nc-TiC/a-C:H have been deposited by reactive magnetron sputtering at substrate bias values of -240 V and -91 V. The films were characterized by XPS, Raman scattering, XRD, ERDA, hardness and tribological measurements. Coatings deposited at -240 V show a hardness enhancement for a-C:H phase contents in the range 10 to 30 % with TiC grain sizes around 5 nm. A less pronounced hardness enhancement is observed for films deposited at -91V. The substrate bias is crucial in obtaining increased hardness of nc-TiC/a-C:H nanocomposite thin films. The hardness of the films, among other mechanical properties, is controlled by the grain size and mean grain separation. Coatings with increased hardness are characterized by mean grain separation of 0.3 nm, which is achieved at bias values below -150 V. The larger mean grain separation of samples deposited at -91V leads to smaller hardness values. Coefficients of friction against steel lower than 0.3 are found for films with mean grain separations as low as 0.1 nm. Self-lubrication due to a-C:H can explain the observed friction behavior. In contrast to the hardness of the coatings, their friction behavior is not affected by the substrate bias.
10:50 AM		B8-3-8 Preparation and Characterization of Superhard Amorphous Carbon Films up to 10 µm Thickness V. Weihnacht, B. Schultrich, P. Siemroth (Fraunhofer Institute for Materials and Beam Technology, Germany) Due to their exceptional high hardness and low friction coefficient hydrogen-free diamond-like carbon coatings are suitable for tribological applications under extreme conditions, for instance as ultrathin protection layers on magnetic storage media. Such films with sp³ contents up to 80% have been deposited using filtered high-current arc technique. These ta-C films show high hardness up to 60 GPa but suffer from high compressive stress in the range of 5 GPa. That stress is a large driving force for film delamination and limits the maximum film thickness usually to some hundred nanometers. In this work, a special design of the film/substrate interface in the nanometer range was developed to deposit ta-C films up to 10 µm thickness on steel substrates without adhesion problems. Tribological testing of these films revealed an excellent wear-resistant behavior. Another possibility used to prevent delamination and to increase the film toughness without significant loss of hardness was nanostructuring of the film. Several deposition parameters such as carbon ion energy, incident angle and gas atmosphere have been used to vary the coating properties in the nanometer range periodically and gradually. These multilayered and graded coatings are compared to pure ta-C films, to Me/C multilayers and to Me+C nanodisperse films with respect to their tribological performance.
11:10 AM		B8-3-9 Synthesis and Microstructures of Carbon Films with Nano-sized Metal Particles W.Y. Wu, J.M. Ting (National Cheng Kung University, Taiwan, ROC) A number of metal containing diamond-like carbon thin films were prepared using a reactive sputter deposition technique. Effects of several growth parameters, including reactive gaseous composition, growth time, and power wattage, on the film characteristics were addressed. The metallic sputtering target materials used include Ni, Cu, and Pt. It is noted that Ni and carbon form carbide, Cu and carbon are immiscible, and Pt is a noble metal. They exist in the resulting films as uniformly distributed nanoparticles with various sizes, depending on the metal type and growth parameters. The size ranges from less than 3 nm to about 15 nm, in diameter. Correlation between the deposition rate and composition was studied. Crystallinity and microstructure of the resulting films were analyzed using micro-Raman microscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The surface chemistry was also examined using electron spectroscopy for chemical analysis (ESCA).