AVS2002 Session SE+TF-TuA: Systems Design of Functional Coatings

Tuesday, November 5, 2002 2:00 PM in Room C-111B

Tuesday Afternoon

Start	Invited?	Item
2:00 PM	Invited	SE+TF-TuA-1 Mechanical Design of Coated Systems Based on Elastic Surface Contacts T. Chudoba (Federal Institute of Materials Research and Testing, Germany); N. Schwarzer, I. Hermann, F. Richter (TU Chemnitz, Germany) Problems in contact mechanics can be solved very conveniently using analytical solutions, even for layered systems and non-axissymmetric systems involving friction. The calculation time is much lower than for finite element calculations, especially for non-axissymmetric problems, and allows an optimization in a large parameter field, which is difficult to achieve with other methods. In many cases, with a foreknowledge of the type of failure to be avoided, the elastic stress fields computed permit critical values of stress to be avoided by a change in input parameters. One of the key requirements of an analytical solution to a contact problem is the availability of accurate and representative values of material properties. Such properties are not generally available for thin film systems where mechanical properties may not be the same as the bulk properties. The present work shows how elastic modulus and yield stress can be obtained experimentally using nanoindentation techniques for films down to a thickness of some nanometres. Results are given for several film substrate combinations. The parameters can be used for a mechanical modelling to optimize film thickness or to find the required mechanical properties of an intermediate layer to withstand a Hertzian contact at the surface. This is demonstrated by some calculations. In another example ternary (B,C,N) films on Si and fused silica produced by magnetron sputtering with a modulus range of 130 GPa to 300 GPa are used. The mechanical properties so obtained are then used as inputs in an analytical model to determine the optimum thickness and properties of an interlayer for a particular loading configuration, that of contact with a spherical indenter. The work extends the analytical treatment to nearly any cases of indenter shape by showing how the results of individual elastic analytical solutions can be assembled and solved using boundary element methods.
2:40 PM		SE+TF-TuA-3 A Combinatorial Sputtering Approach to Properties Modification in Polaron Conducting Films R.R. Owings, P.H. Holloway (University of Florida); C.F. Windisch, Jr., G.J. Exarhos (Pacific Northwest National Laboratory) The influence of sputtering parameters and cation composition on measured resistivity and optical transparency of mixed transition metal spinel oxides (AB₂O₄) has been systematically studied. A two-cathode system was used to deposit films having continuously variable compositions onto glass, silicon, and sapphire substrates (25 mm in length) as a function of process gas composition and pressure, target to substrate distance, substrate temperature, sputtering power, and sputtering time. The intent was to correlate transparency and conductivity with composition, phase purity, grain size, film thickness, and cation oxidation state. Both mixed metal oxide and metal alloy targets (nickel, cobalt, rhodium, palladium) were used for sputter deposition with variable gas mixtures of argon and oxygen. Post deposition annealing of sputtered films was found to lower film resistivity but had little effect on optical transparency. Film resistivity returned to its original value upon standing in air for two weeks. However, partial substitution of lithium for cobalt was found to not only improve the conductivity and increase transparency but also to significantly reduce property variations when subjected to post deposition annealing in air. Results suggest that the presence of lithium stabilizes higher oxidation states of the resident transition metal cations leading to lattice compression and diminished oxygen transport.
3:00 PM		SE+TF-TuA-4 Profile Coatings and Their Applications C. Liu, L. Assoufid, A. Macrander (Argonne National Laboratory); G. Ice, J. Tischler (Oak Ridge National Laboratory); K. Zhang (Illinois Institute of Technology) We report a method of profile coating to achieve a certain pre-selected thickness profile of a thin film coating using dc magnetron sputtering. In profile coatings, the substrate is passed over a contoured mask at a constant speed to obtain a desired profile along the direction perpendicular to the substrate-moving direction. The shape of the contour depends on the desired profile and the thickness distribution directly above the gun at the substrate level. Four-inch-diameter Si wafers were coated through a 100 x 152 mm² aperture on the top of the shield can. The thickness distribution was then obtained using a spectroscopic ellipsometer with computer-controlled X-Y stages. A model has been developed to fit the measured thickness distribution. The relative thickness weightings are then digitized at every point 1 mm apart for the entire open area of the aperture. When the substrate is moving across the shield can during depositions, the film thickness is directly proportional to the length of the opening on the can along the moving direction. By equating the summation of relative weighting to the required relative thickness at the same position, the length of the opening at that position can be determined. By repeating the same process for the whole length of the required profile, a contour can be obtained for a desired thickness profile. The contoured mask is then placed very close (~1 mm) to the substrate level on the shield can opening. The number of passes and the moving speed of the substrate are determined according to the required thickness and the growth rate calibration. This method of profile coating has been applied to coat laterally graded W/C multilayers for tunable x-ray double-monochromator and x-ray fluorescence detection applications. It has also been applied to coat Au on a cylindrical mirror to obtain an elliptical mirror for x-ray focusing applications. Test results for these applications will be presented.
3:20 PM		SE+TF-TuA-5 Nano-Structure Substoichiometric Zirconium Nitride Coatings with Unique Metallic Colors and Superior Abrasion and Corrosion Resistance G. Chen (Vapor Technologies, Inc.); J.S. Lipe, P.B. Jonte (Delta Faucet Company); S. Moysan (Baldwin Hardware Company) Low temperature arc vapor deposition (LTAVD) is one of the widely applied techniques for industrial production of decorative and functional coatings. Nickel and stainless steel color protective coatings were deposited using substoichiometric nano-crystal size zirconium nitride and oxynitride. Generally the total amount of nitrogen and oxygen is between about 14 to about 50 atomic percent with a nitrogen content of at least about 6 atomic percent. The slightly nitrided or nitrided and oxidized color layer is mainly comprised of nano-phase to amorphous metallic refractory metal with textured metal nitride phase, as determined using x-ray diffraction. For example, zirconium nitride primarily oriented in (111) plane and smaller than 50 nm in grain size, or metallic zirconium primarily oriented in (112) plane and smaller than 80 nm, depending on the proportion of oxygen in total gas flow. Such types of structures are produced at relatively low processing pressures, ranging from 1 to 5 millitorr. These nano-phase coatings have superior abrasion resistance and corrosion resistance over the relative large crystal size coatings have the same atomic percent of nitrogen content.
3:40 PM		SE+TF-TuA-6 The Adhesion Behavior of Alumina-based Ceramic Nanocoatings and Nanostructures M.V. Kireitseu, I.A. Nemerenco, L.V. Yerakhavets, M. Istomin (Institute of Machine Reliability, NAS, Belarus) The adhesion behavior of alumina-based ceramic coatings and alumina-based nanostructures involved CrC nanoparticles in contact with themselves, metals and polymer surfaces is strongly dependent upon the chemistry of the ceramic surface and that of the solids with which contact is made. With clean alumina-based ceramic coating surfaces in contact crystallographic orientation influences adhesion as determined by friction force measurements. Friction force measurements are especially effective in gaining quantitative information on interfacial bond strengths. Ceramics, just as has been observed with metals, exhibit the smallest adhesive bond forces and accordingly the lowest friction for the high atomic density low surface energy crystallographic planes. This has been observed with oxide ceramics such as aluminum oxide and nanocomposites based on alumina matrix and chrome carbide nanoparticles. For metals contacting alumina-based ceramic coatings again the chemical activity of the metal is important to adhesive behavior. With noble metals silver and gold interfacial adhesive bonds were sufficiently weak so as not to result in separation of damage to the surfaces of the contacting solids. With other metals that form stable oxides, the interfacial adhesive bonds were sufficiently strong so as to result in fracture of single crystal sapphire when cleavage planes were parallel to the contact interface. Metals undergo shear when the alumina-based ceramic coatings is poly-crystalline aluminum oxide matrix of alpha and gamma phases and attempts are made to, by tangential motion, to fracture the adhered interface. Adsorbates reduce singificantly adhesion and friction forces.
4:00 PM		SE+TF-TuA-7 Adhesion Fundamentals and Nanomechanics in Alumina-diamonds Nanocomposites M.V. Kireitseu, L.V. Yerakhavets, I.A. Nemerenco (NAMATEX System Division, Institute of Machine Reliability, Russia) When alumina-based ceramic coatings are brought into contact with a ceramic, a polymer, or a metal, strong bond forces can develop between the materials. The bonding forces will depend upon the state of the surfaces, cleanliness and the fundamental properties of the two solids, both surface and substrate. Adhesion between alumina-based ceramic coatings and another solid are discussed from a theoretical consideration of the nature of the surfaces and experimentally by relating bond forces to the interface resulting from solid state contact. Surface properties of alumina-based ceramic composites correlated with adhesion include orientation, reconstruction, and diffusion as well as the chemistry of the surface specie. Where a ceramic is in contact with a metal their interactive chemistry and bond strength is considered. Substrate properties examined include elastic and plastic behavior in the surficial regions, cohesive binding energies, crystal structures, and crystallographic orientation. Materials examined with respect to interfacial adhesive interactions include alumina composite hardened by chrome carbide nanoparticles and diamonds nanoparticles and aluminum oxide. The surfaces of the contacting solids are studied both in the atomic or molecularly clean state and in the presence of selected surface contaminants.
4:20 PM		SE+TF-TuA-8 Nanoindentation of Alumina - Chrome Carbide and Alumina - Ultra Dispersed Diamonds nanoComposites L.V. Yerakhavets, M.V. Kireitseu, I.A. Nemerenco (NAMATEX System Division, Institute of Machine Reliability, Russia) Nanoindentation experiments have been done on alumina-chrome carbide and alumina-ultra dispersed diamonds nanocomposite coating on different substrates like steel, aluminum and corundum. Films with thicknesses between 60 and 300 ?m prepared at various current intensities were indented with spherical indenters with nominal radii of 10, 50, and 150 ?m. The influence of deposition current and drying conditions were investigated using SEM. The suitability of this technique to determine morphology and the use of small spherical-tipped indenters to evaluate the mechanical properties of powder compacts was established. The revealed results may be summarized as follows: (1) The structure, grain size and morphology strongly depend on deposition current although the film density does not. At low current intensity, the grain size is found to be close to the initial particle size, whereas at higher current intensity an apparent coarser grain size occurs that, however, also contains pores and internal voids. (2) it is expected that the higher over potential results in the coarser grain size and formation of pores at higher current intensity that caused the onset of electrolysis of the aqueous medium. The localized electrolysis and oxygen evolution near the anode, resulting in a localized change in pH of the aqueous suspension, produced particle agglomeration as well as bubble formation. (3) Spherical indentation technique is found to be effectively measured contact pressure and effective elastic modulus as a function of penetration depth. The difference in contact pressure and elastic modulus vs. the indenter depth could be adjusted by the modulus vs. the ratio of the contact radius to the film thickness. The errors in the data could be also associated with radial cracks within the contact area. (4) Evidence of residual tensile stresses within the film manifested itself in the form of radial cracks from pores. The thicker films showed a greater influence of the cracks. ¹none
4:40 PM		SE+TF-TuA-9 Rheological Behaviour of Alumina-Diamonds-Polymer NanoComposite Structure I.A. Nemerenco, M.V. Kireitseu, L.V. Yerakhavets (NAMATEX System Division, Institute of Machine Reliability, Russia) To predict strength and deformation of the alumina-diamonds-polymer nanocomposition under Hertzian indentation the rheological model has been developed. The model is based on combined simple rheological elements that in general gives accurate results in comparison with one obtained in Hertzian indentation technique. Based upon the investigations we have suggested the following requirements to be used in rheological model of the nanocomposite structure: 1. Since the composite include hard alumina layer and steel substrate that exhibit plasticity, the irreversible deformations has to be considered as plastic in nature. Deformations develop only after excess of some critical yield strength for the particular layer of the composite. 2. if the deformations are smaller then yield strength, the deformations at constant stress have to grow up step-by-step to final value; 3. Cyclic loading increases summarized plastic deformation of the composite; 4. Curve of deformation vs. time at constant load exhibits a linear dependence in one of plotted region. 5. At unloading the retardation of deformations (elastic return) has to be observed; 6. Stress at constant deformations is relaxed. The selection of model that adequate to the studied composite material is determined by comparison of developed models and experimental results. The composite of hard alumina-diamonds-aluminum can be presented as elastic-tenacious-plastic rheological model of the composite. The mechanical prototype of the model is described in a book. Structural equations of the integral model of the composite looks like (H \|\| N \|\| St-V) - (H-N \|\| H). In general, the kind of the rheological equation depends on a level and form of stress applied on model. The polymer layer can be presented as the rheological model consisting from two elastic elements and one tenacious element. As a prototype of the model, we can consider connection of the Maxwells' model and elastic element. The composite exhibits linear relation of stress curve, whereas unloaded composite shows retardation of deformations (elastic return) shown as downfall segment of the curve. The plotted relations of experimental data and calculated data have revealed very close agreement of developed rheological model and real mechanical behavior of the composite. The above stated conditions are found to be used in investigations of mechanical and rheological properties of the alumina-aluminum-polymer-steel composite systems. The rheological properties and perspectives to be considered in development of such nanocomposite structure have been discussed.
5:00 PM		SE+TF-TuA-10 Adhesion of Alumina-based Nanocomposites to Polymer Substrate A.G. Fedaravichus, M.V. Kireitseu, I.A. Nemerenco (NAMATEX System Division, Institute of Machine Reliability, Russia) Adhesion bonding of alumina-based nanostructures to several polyimides has been studied as a function of technological parameters of the layers deposition and polymer surface modification by ion beam and chemical pretreatment. The effects of the alumina-based layer deposition method and parameters have also been examined. The materials of interest include a low thermal expansion polyimide derived from 3,3,4,4-biphenyl tetracarboxylic acid dianhydride-p-phenylene diamine (BPDA-PDA) polyamic acid, and pyromellitic dianhydride-4,4-oxydianiline (PMDA-ODA) polyimide, formed from polyamic acid or polyamide ethyl ester precursors. The alumina/polyimide adhesive strength was determined by the scratch peel test, while the interfacial regions were examined using x-ray photoelectron spectroscopy and ellipsometry. It is found that for PMDA-ODA systems, exposure to low energy Ar + and/or O2+ ions improves adhesion of the alumina-based nanooverlayer, while for BPDA-PDA polyimide, the role of O2+ is more significant. The fracture location is found to lie 20-300 A within the polymer, depending upon the ion beam dose and the specific polyimide employed.