ICMCTF2008 Session E1-3: Friction and Wear of Coatings: Lubrication, Surface Effects and Modeling

Tuesday, April 29, 2008 8:00 AM in Room California

Tuesday Morning

Start	Invited?	Item
8:00 AM	Invited	E1-3-1 Tribology of Hard Coatings Alloys Deposited by Thermal Methods: Applications to Industrial Components R.H. Conde, G.E. Carr (INTEMA, Universidad de Mar del Plata, Argentina) In most of seamless tube making industries, the service life of mandrels used for rotary forging is less than 350 perforation events, despite in some cases the tool lasts longer than 1000 perforations. Being the first of a series of hot working steps, an improvement during the piercing multiplies the benefits throughout the whole manufacturing process. Mandrels are cast in three metal bases: iron, nickel and cobalt, but lower costs support the use of iron base alloys, mostly when larger mandrel diameters are required. Mandrels life is usually improved by the controlled growth, at high temperature, of a hard oxide film. The research reported in this work is related to the protective oxide films grown on mandrels for seamless tube rotary forging¹. A laboratory scale equipment has been entirely designed and built at INTEMA in order to study mandrels wear during rotary piercing of steel billets. Hard coatings oxides grown under controlled atmosphere on mandrels surface were tested by this equipment, reproducing the same wear conditions observed at industrial scale. Wear and oxide film evolution were studied by optical microscopy and energy-dispersive X-ray spectroscopy. Acquired data from lab-scale piercing experiments were analyzed using neural networks (self organizing maps) in order to find out relationships among 22 process parameters and oxide film characteristics. It is suggested that this method of analysis could be applied to any industrial component under multivariable hard coating wear situations. ¹ The present work is part of G.E.Carr's Ph.D. Thesis at University of Mar del Plata, Argentina.
8:40 AM		E1-3-3 Endurance of a Solid Lubricant Subjected to High Temperature Fretting Wear C. Mary, S. Fouvry, J.-M. Martin (Ecole Centrale de Lyon, France); B Bonnet (Snecma, Site de Villaroche, France) Fretting wear is a surface degradation process invariably observed when two contacting body are subjected to small amplitude oscillatory movements. In the blade/disk contact of aero-engines especially, movements induced by the engine regime changes may lead to critical wear. In order to limit friction and protect components, motorists usually use a multi-coatings system composed of a thick and soft Cu-Ni-In layer (150µm) covered by a thin graphite solid lubricant (15µm). This system is subjected to high contact pressure (up to 500MPa) and high temperatures (up to 500°C). This paper focused on the evaluation of the efficiency and endurance of such a system. An experimental layout was designed to perform fretting-wear tests up to 500°C. Several geometries close to industrial contacts were studied and commercial titanium alloys (Ti17 and Ti6242) coated with Cu-Ni-In and solid lubricant were tested. A transition from a lubricated phase to a major wear phase was pointed out and attributed to the degradation of the solid lubricant depending on tests conditions. This degradation was studied tribo-chemically via the analysis of debris generated (XRD and TEM) and the observation of the evolution of the surface. Lubricant endurance was also evaluated mechanically following an energy capacity approach.
9:00 AM		E1-3-4 Smart Tribological Coatings With Wear Sensing Capability C. Muratore (Air Force Research Laboratory (AFRL/RXBT)/UTC, Inc.); D.R. Clarke (University of California, Santa Barbara); J.G. Jones (Air Force Research Laboratory (AFRL/RXBT)); A.A. Voevodin (Air Force Research Laboratory) Nanocomposite coatings demonstrating multiple temperature adaptation mechanisms have been deposited with a hybrid physical vapor deposition process to provide solid lubrication from room temperature to 700 °C. To further facilitate the development of improved multilayered adaptive coatings and to promote their use in real systems, an in situ wear measurement system was developed to allow automatic reporting of remaining wear life while in use. Monitoring of coating health was achieved by embedding sensor layers, known to produce distinctive luminescence spectra when exposed to laser illumination, at different depths throughout the thickness of solid lubricant coatings. One example of the current work employed erbium- and samarium-doped yttria stabilized zirconia (YSZ) as sensor materials. The YSZ-Er sensor layer was placed approximately midway through a 3 µm molybdenum disulfide coating, and the YSZ-Sm layer was located at the coating/substrate interface. Placement of the luminescent coatings in these positions allowed detection of wear depth and provided a clear warning of impending coating failure during testing. The soft MoS₂ coatings with the imbedded ceramic sensor layers also demonstrated long wear lives (200,000 cycles) in humid air compared to monolithic MoS₂ coatings(<10,000 cycles) with the same total thickness, microstructure, morphology and composition. The mechanism for the observed wear life increase was examined and discussed together with the use of embedded wear sensors in other tribological coatings.
9:20 AM		E1-3-5 Lubricous ZnO/Al₂O₃ Nanolaminates Grown by Atomic Layer Deposition: Composition, Microstructure and Tribological Behavior M.C. Romanes, T.W. Scharf (The University of North Texas) ZnO and Al₂O₃ bilayers were grown up to 200 nm thickness via atomic layer deposition (ALD) in a nanolaminate geometry. The bilayer thickness, which varied from ~1.5 to 100 nm/layer, was investigated for potential high temperature lubricous oxide (solid lubricant) applications. The effects of growth temperature (200, 250 and 350°C) and interfacial density (1, 8, 16 and 64 bilayers) on the friction and wear behavior of the nanolaminates were explored. Ex-situ grazing incidence x-ray diffraction, atomic force microscopy, high-resolution scanning and transmission electron microscopies were employed for surface and microstructural analyses. Complementary x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy analyses were used for compositional interrogation. Results indicate that smaller ZnO grain size and a dominance of (002) grains are desirable for better friction and wear behavior. The amorphous Al₂O₃ layer played a more important role in preferred orientation of ZnO in the nanolaminates than acting as a load bearing layer. The friction tests showed that the 1 and 8 bilayers exhibited the lowest friction coefficient of ~0.18 to 0.22 in ambient air and dry nitrogen, followed by ~0.3 for pure ZnO layer and higher values of >0.4 for 16 and 64 bilayers. Mechanisms involving composition, structure, and tribological property interrelationships will be discussed.
9:40 AM		E1-3-6 HVOF Sprayed WC-Co as Hard Interlayer for DLC Films G. Bolelli, L. Lusvarghi, F. Pighetti Mantini (University of Modena and Reggio Emilia, Italy); F. Pitacco, H. Volz (Protec Surface Technologies S.r.l., Italy); M. Barletta (Università di Roma Tor Vergata, Italy) DLC films show outstanding properties such as high hardness, very low friction coefficient against most materials and chemical inertness. However, when a significant difference in hardness exists between the DLC film and the substrate, its adhesion and tribological performance are impaired. Using a thick, hard interlayer between substrate and DLC film can largely overcome these troubles. Therefore, this study evaluates the technical improvement achieved by applying a thick HVOF-sprayed WC-17Co interlayer between a DLC thin film and a C40 steel substrate. The chemical composition (from XPS analysis) and hardness (from nano-indentation test) of the DLC films deposited on both bare and HVOF-coated C40 steel are analogous. Nevertheless, the better adhesion of the DLC film on WC-17Co interlayer is demonstrated by higher critical loads recorded in scratch testing. During ball-on-disk dry sliding tribological tests, when contact pressures are limited (6mm diameter ball, 5N normal load), the adhesion between DLC and C40 steel substrate is sufficient to achieve very low wear rates, both at room temperature and at 300°C; however, under high contact pressures (3mm diameter ball, 10N normal load), the DLC film on bare C40 steel undergoes severe delamination at both test temperatures, while a significant improvement is achieved by using the WC-17Co interlayer.
10:00 AM		E1-3-8 Tribological and Mechanical Properties of HFCVD Diamond-Coated WC-Co Substrates With Different Cr Interlayers C.-C. Chou (National Taiwan Ocean University, Taiwan); J.-W. Lee (Tung Nan University, Taiwan); Y.I. Chen (National Taiwan Ocean University, Taiwan); J.-S. Yang (Tung Nan University, Taiwan) Two chromium interlayers were coated on WC-Co substrates for improving performance of diamond surface coatings by using pack chromization and bipolar symmetry pulsed DC reactive magnetron sputtering processes. Daimler-Benz Rockwell-C indentation tests were conducted to evaluate the adhesion properties of diamond coatings with these two interlayers. No delamination outside of the indentation zone was observed by a scanning electron microscopy (SEM) for the diamond coatings deposited on both chromized interlayers. Wear resistance of both coatings were also investigated by pin-on-disk wear tests. Rather low wear volumes revealed their excellent anti-wear behavior. Both chromized surfaces were found partially transformed into carbide compound layers by X-ray diffractometer (XRD). Good diamond adhesion on chromized interlayers has been attributed to chromium carbide formation on pack chromized film surfaces as well as on PVD ones during the hot filament chemical vapor deposition (HFCVD) process. It is concluded that the adhesion properties and tribological performance of CVD diamond coatings were significantly improved by the proposed chromized interlayers. However, the choice of industrial application between them could be relied on the economical view point.