Papers

ICMCTF2005 Session B8-3: Hard and Multifunctional Nano-structured Coatings

Wednesday, May 4, 2005 1:30 PM in Room Golden West

Wednesday Afternoon

Start	Invited?	Item
1:30 PM		B8-3-1 Structure of Sputtered nc-Cr-C/a-C:H Thin Films G. Gassner (University of Leoben, Austria); E. Hegedũs, I. Kovacs, L. Tóth, B. Pécz (MFA Research Institute for Technical Physics and Materials Science, Hungary); J. Patscheider (EMPA, Switzerland); P.H. Mayrhofer, C. Mitterer (University of Leoben, Austria) Amorphous hydrogenated carbon (DLC or a-C:H) coatings have been the subject of intensive research activities within the last two decades due to their superior mechanical and tribological properties. Recently, a nanocomposite (nc) concept for severe tribological applications, where metal carbides, providing enhanced wear resistance, are embedded in a lubricating a-C:H matrix, has been proposed. The aim of this work is to investigate the structure of nc-Cr-C/a-C:H coatings prepared by unbalanced magnetron sputtering (UBM) of a metallic Cr target in an Ar/CH₄ discharge. These nc-coatings can be subdivided into hard, chromium carbide (Cr-C) dominated films, when prepared at low CH₄ to total pressure ratios (pCH₄/pT < 0.4) and into low-friction, a-C:H dominated films, when prepared at pCH₄/pT > 0.4. X-ray diffraction and Raman spectroscopy were used to characterize the phase composition of both coating types. The results were correlated to the chemical composition obtained by Rutherford backscattering and elastic recoil detection analysis. Additionally, X-ray spectroscopy was used to determine the chemical bonding within the various films. Finally, the coating microstructure was investigated on selected samples by transmission electron microscopy. The structure of the low-friction a-C:H dominated coating was found to consist of 2-10 nm sized Cr-C crystallites embedded into the amorphous matrix. It can be concluded that nc-Cr-C/a-C:H coatings with tailored mechanical and tribological properties can successfully be designed by UBM.
1:50 PM		B8-3-2 Deposition of Highly Hydrogenated Carbon Films by a Modified Plasma Assisted Chemical Vapor Deposition Technique B. Shi, W.J. Meng (Louisiana State University) Ceramic nanocomposite coatings consisting of nanoscale mixtures of two or more phases have been intensely investigated. Advanced macro- and micro- scale manufacturing operations often demand coatings which are functional at higher temperatures. Thermomechanical behavior of ceramic nanocomposite coatings are therefore of scientific as well as practical interests. We present recent results on characterization of low and high temperature deposited Ti-containing hydrogenated carbon (Ti-C:H) coatings. We report results of thermal expansion measurement on Ti-C:H coatings, as well as characterization of structure and thermal stability of Ti-C:H coatings.
2:10 PM		B8-3-4 Properties of Al_1-xCr_xN Films Synthesized by Closed Field Unbalanced Magnetron Sputtering with Vertical Magnetron Sources G.S. Kim, S.Y. Lee (HanKuk Aviation Unversity, South Korea); J.H. Hahn (Korea Research Institute of Standards and Science, South Korea) The binary nitrides such as TiN, CrN, AlN and etc. have been widely used as protective, wear resistant coatings for cutting tools because of their excellent properties. However, they were not suitable for high-speed cutting tools used at temperatures as high as 800°C because of their low oxidation temperature. Thus, it was needed to develop coatings having a higher oxidation temperature than 800°C. To further improve the oxidation resistance of binary coatings, alloying with another metal to form a ternary hard coating was explored and then the various ternary nitrides such as TiAlN, TiCrN and CrAlN have been developed. Recently, AlCrN coatings having superior oxidation resistance and higher wear resistance than CrAlN films have been published. But information about the properties of AlCrN coatings are still very scarce in spite of the their high performance. In this study, the properties of AlCrN films as a function of the Cr content were studied and compared to the CrAlN films. The AlCrN and CrAlN coatings were deposited by closed field unbalanced magnetron sputtering with vertical magnetron sources and their structure, crystal phase and mechanical properties were investigated by Auger electron spectroscopy (AES), X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), scanning electron microscopy (SEM), nanoindentation, high-temperature oxidation and wear tests. The detailed analysis results of films will be presented.
2:30 PM		B8-3-5 Growth and Characterization of Nanocomposite Yttria-Stabilized Zirconia with Ag and Mo C. Muratore, A.A. Voevodin, J.J. Hu, J.J. Jones, J.S. Zabinski (Air Force Research Laboratory) Thin films composed of yttria stabilized zirconia (YSZ) nanocrystals imbedded in an amorphous YSZ-gold matrix have shown high fracture toughness, low friction coefficients and other desirable mechanical properties at room temperature and up to 500°C.¹ In the current work, silver and molybdenum were substituted for gold to improve the mechanical properties of adaptive nanocomposite thin films in a broader temperature range. YSZ films containing up to 70 percent metal were deposited in a hybrid pulsed laser/magnetron deposition system. Film structure and composition were characterized using X-ray photoelectron spectroscopy, X-ray diffraction, and electron microscopy. Nanoindentation and ball-on-disc techniques were employed to measure mechanical properties of the YSZ-metal composites. Friction coefficients in the range of 0.2-0.4 were measured for YSZ-silver films for sliding against silicon nitride balls in air at 500°C. In situ examination of the films in the transmission electron microscope during heating showed nucleation and growth of metal phases at the film surface, resulting in a lubricating surface at high temperature. The effect of additional solid lubricant reservoirs on the tribological properties of YSZ-metal films was also explored. ¹ A.A. Voevodin et al. Surf. Coat. Technol, 146-147, 351 (2001).
2:50 PM		B8-3-6 Role of the Interface in the Mechanical Properties of nc-ZrN/a-M (M=Ag, Au, or Pd) Nanocomposite Films S.M. Aouadi, S. El-Hanafi, A. Bohnhoff, P.K. Shreeman, Q. Ge (Southern Illinois University); J. Xu, S.R. Mishra (University of Memphis); P. Filip (Southern Illinois University) Nanocomposite films of ZrN/M (M= Ag, Au, or Pd) were prepared using reactive unbalanced magnetron sputtering and their structural, chemical, and mechanical properties were investigated as a function of film composition and substrate bias. X-ray diffraction spectra and TEM micrographs revealed that the films formed nanocrystals of ZrN with a crystallite size of about 10 nm, embedded in a metal M matrix. The grain size was found to decrease with metal content. The chemical and phase composition were deduced from X-ray photoelectron spectroscopy and Rutherford Backscattering. The nanohardness and elastic modulus was measured by the nanoindention technique. The resistance to plastic deformation, as measured by the ratio H3/E2, was optimized and was found to depend on the choice of the metallic element. These findings were attributed to the bonding mechanism at the interface between the ceramic nanocrystals and the metallic matrix as shown using ab-initio calculations using density functional theory calculations.
3:10 PM		B8-3-8 Nanocomposite Alumina-Zirconia Thin Films by Dual RF Magnetron Sputtering from Oxide Targets D.H. Trinh, H. Högberg, J. Andersson (Linköping University, Sweden); M. Collin, I. Reineck (AB Sandvik Tooling, Västberga, Sweden); U. Helmersson, L. Hultman (Linköping University, Sweden) Ceramic alumina coatings are of technical interest for many applications. Additions of tetragonal zirconia to alumina ceramics have been shown to improve the toughness of bulk alumina, indeed bulk zirconia-alumina ceramics are already used in cutting tool applications. The production of hard composite alumina-zirconia coatings may therefore be of interest for the development of tougher cutting tools. In this study dual RF magnetron sputtering of oxide targets was employed to produce oxide coatings on silicon (100) substrates at a relatively low substrate temperature of 450°C. Composite alumina-zirconia films were produced with a range of compositions in addition to films of pure alumina and zirconia. X-ray diffraction showed monoclinic zirconia in the films of pure zirconia, addition of alumina caused the tetragonal phase of zirconia to form instead of the monoclinic phase. Furthermore, the observed peaks were diffuse, indicating that the films were nanocrystalline. The tetragonal zirconia phase is associated with the main toughening mechanism in bulk alumina-zirconia ceramics, namely the tetragonal-to-monoclinic phase transformation with associated volume expansion. The stabilization of the tetragonal phase in composite films is thus a positive indication that tough alumina-zirconia coatings can be produced. Results from TEM and nanoindentation investigations will be presented.
3:30 PM		B8-3-9 Applications of TiAlN- and TiO₂-Coatings with Nanoscale Surface Topografies F. Burmeister, G. Kleer (Fraunhofer Institute for Mechanics of Materials, Germany); A. Gombert, B. Blaesi (Fraunhofer Institute for Solar Energy Systems, Germany) This paper is to report on the development of nanostructured, multifunctional TiAlN and TiO₂ - coatings. Their multifunctionality is due to their special growth mode and surface morphology: Both coatings exhibited a columnar growth mode with diameters of the individual columns between 100nm and 500nm. The columns were terminated by pyramid-shaped tips where the geometric forms of the pyramids were determined by the crystal system of the coating material. The coatings were sputter-deposited on silicon and steel substrates by a reactive RF-magne-tron process under variation of total pressure, reactive gas flow and RF-power. Investigations of microstructure and surface mor-phology were carried out with electron microscopy (SEM), atomic force microscopy (AFM) and x-ray diffraction techniques (XRD). A power law was found for the depen-dance of the mean column diameter on coating thickness in qualitative agreement with pheno-meno-logical models for thin film growth. For industrial applications, both coating materials were deposited on steel tools and replicated into the surfaces of PMMA- sheets. The resulting screen's surface morphologies proved to be comparable to the anti-reflective surfaces of moth-eyes and led to a pronounced decrease in reflectivity. This opens up a way for a cheap mass production of clear-view-screens e.g. for mobile phones by injection mouklding techniques. Further applications for such nanostructured coatings in combination with wet chemical processes, e.g. silanization, are the fabrication of superhydrophobic surfaces.