ICMCTF2007 Session TS1: Coatings for Aerospace Applications
Wednesday, April 25, 2007 1:30 PM in Room Golden West
TS1-6 Research Experience on Performance of Coated Gears and Bearings
T.L. Krantz (Army Research Laboratory)
Mechanical and aerospace engineers have had keen interest in using coatings to improve the performance of mechanical components such as gears and bearings for a number of years. The Army Research Laboratory's Vehicle Technology Directorate and the NASA Glenn Research Center's Mechanical Components Branch has done research on the use of coated components for aerospace applications. For gears, experiments were conducted to investigate coatings to enhance surface fatigue life, reduce wear, and improve performance after loss of oil supply. For journal bearings, we have considered coatings as an enabling technology for certain applications for high-power density gearboxes. Coatings are considered as required for wave-geometry journal bearings to survive start-stop conditions and loss of oil supply. Experiences with coatings, good and bad, will be discussed.
TS1-3 Investigation of Abradable Seal Coating Performance using Scratch Testing
X. Ma, A. Matthews (University of Sheffield, United Kingdom)
Abradable seal coatings are widely used in gas turbines as sacrificial layers to accommodate the rubbing between the blades and the outer casing, ensuring that gaps between them can be minimised in order to optimise engine performance. @paragraph@The majority of reported evaluations of coating abradability have been restricted to the simulation of the actual conditions during service. Industry also connects abradability with other mechanical properties such as hardnesses (measured using R15Y tests), Ultimate Tensile Strength (UTS) and elastic modulus.@paragraph@Since the real conditions at the blade-tip and the casing present a complex (very high speed) deformation situation that is difficult and expensive to replicate, our study was aimed at evaluating the use of a (low speed) standard scratch tester, as a means of assessing the performance of abradable coatings. Three proprietary plasma-sprayed coatings, Ni-graphite, Al-Si-graphite and Al-Si-polyester, were chosen for the tests. The scratch test behaviour was correlated with mechanical properties of the coatings (elastic moduli, microhardness and UTS). The results obtained were compared with results of industrial trials, to thereby ascertain if the scratch test could be used as a cheap and effective alternative to expensive engine trials. We have shown that the "ospecific grooving energy" (also called "odynamic hardness") can be utilised as a measure of abradability in the scratch test, and can be related to the mechanical properties, in a manner consistent with test-bed findings. We have also found the abradability can change with scratch length due to coating "odensification" ahead of the slider, which is not easily revealed by other tests (such as the pendulum method). We therefore believe that scratch testing is a useful means of evaluating the likely in-service performance of abradable coatings, prior to carrying out engine trials. It can be used to assist in the optimisation of abradable coatings.
TS1-4 Friction Coefficient Studies on Hold-Down Systems for Space Mechanisms
L.V. Santos (Instituto Nacional de Pesquisas Espacial INPE, Brazil); P.A. Radi (Instituto Nacional de Pesquisas Espaciais INPE and Instituto Tecnologico da Aeronautica ITA, Brazil); L.F. Bonetti (Instituto Nacional de Pesquisas Espaciais INPe and Instituto Tecnologico da Aeronautia ITA, Brazil); G.C. Rodrigues, V.J. Trava-Airoldi (Instituto Nacional de Pesquisas Espaciais INPE, Brazil)
Low-hydrogenated diamond-like carbon (DLC) films have a high friction coefficient in a vacuum environment, but they show a low friction coefficient in an atmospheric environment. Thus, DLC films acts as solid lubricants in air, so they can be used to minimize friction during the satellite assembly process, and yet in vacuum transition can be used on texturized parts on hold down devices to avoid moving parts and kept its in closed contact during the launching process until the unit reaches deep space. In deep space can be used as a protective coating to avoid metal in contact, prevent cold welding, and to improve panel deployment and operation in a vacuum environment. As a Chameleon-like for DLC changes friction coefficient according the environment. In this study DLC films and tungsten carbide (WC) were tested and compared as protective coatings on hold-down devices with texturized and non-texturized Ti@sub 6@Al@sub 4@V surfaces to keep in closed contact two surfaces in launch configuration. A specific tribosystem was building to study the locked surface, friction coefficient, and adhesion. The test couples were WC/WC and DLC/DLC, with and without texturized surfaces and additional tests were done evaluated DLC friction coefficients under high pressure conditions in air and vacuum environments. The DLC films' hardness was evaluated by micro-indentation. Friction coefficients in air and ultra-high vacuum environments were measured on bodies witness at low sliding speeds by pin-on-disc, as required by spacecraft operation procedures. Raman scattering spectroscopy was also used in order to determine the DLC films' structural characteristics before and after sliding tests to evaluated DLC film chemical signatures. Novelty: very adherent, DLC chameleon-like for high friction coefficients on Ti@sub 6@Al@sub 4@V substrate on locked space components.
TS1-5 SiC and BC Permanent Pretreatments for Mg-Rich Primers
D.L. Schulz, R.A. Sailer, D. Battocchi, B.J. Chisholm (North Dakota State University)
Mg-based primers have been demonstrated to provide galvanic corrosion protection for aluminum and this technology may be amenable to application on legacy aircraft. A pretreatment layer is often applied between the Al substrate and the primer to promote adhesion. In this talk, we will present our results on the development of SiC and BC-based permanent pretreatment layers that are compatible with the Mg-rich primer. SiC and BC thin film on Al-2024 were subjected to various characterizations including hardness, scratch testing, conductivity and gas jet erosion with the latter mimicking the erosive effects of the plastic media used at the depot to strip paint. In some instances, Mg-based primer was coated onto these substrates and the galvanic function of the system was determined by electrochemical impedance spectroscopy before and after accelerated lifetime tests (e.g., salt fog). The permancy of the SiC and/or BC pretreatment layer would be demonstrated when the Mg-rich primer layer is selective media blasted from the surface of the Al-2024/pretreatment substrate. If successfully developed, the value of such a coating is the reduction of a three-component coatings system (i.e., pretreatment, primer, topcoat) to a two-component system (i.e,. primer, topcoat).
TS1-1 Surface Engineering in the Gas Turbine - Current and Future State
D.S. Rickerby (Rolls-Royce plc.)
Today surface engineering plays a major role in achieving the design lives and performance levels of military and civil gas turbine components and, given the demand for higher performance, cleaner and more fuel efficient engines, is likely to be exploited more so in the future. By making reference to the compressor, combustion and turbine modules of the aero gas turbine, the role that surface engineering plays in the design process will be illustrated, and how material/coating systems are increasing being evolved to be capable of responding to a wide range of operating conditions. This move towards smart coating systems will be discussed and potential future directions reviewed.
TS1-8 Fretting Wear-Resistant, Micro-Arc Oxidation Coatings for Aluminum and Titanium Alloy Bearings
K. Choppy, R.F. Kovar, M. Cushman (Infoscitex Corporation)
Aluminum and titanium alloys are used as replacements for steel in gear boxes of aircraft and helicopters in both military and commercial air vehicles, due to their low density, mechanical strength and thermal conductivity. However, these alloys are susceptible to fretting wear when matched to harder steel surfaces under high loads at elevated temperatures. Anodized coatings are too thin and porous to protect these metals. Infoscitex applied a proprietary micro-arc oxidation process to produce hard, thick, and adherent oxide coatings on aluminum and titanium alloys that rendered the coated metal components resistant to fretting type wear. Selected aluminum and titanium alloy test specimens were micro-arc treated then measured for surface hardness, roughness, and adhesion to metal substrate. Block-on-Ring fretting wear tests on polished test specimens against M-50 steel were conducted in the presence of lubricant, under high loading, at ambient and 400@super o@F temperatures. Coefficient of friction and wear volume were measured versus number of test cycles. The results of efforts to improve the fretting wear resistance of aluminum and titanium alloy bearings for use in aircraft gear box applications will be discussed.
TS1-9 High Temperature PFPAE Lubricant Corrosion Performance of Dual Segment Nanostructured TiCrN + BCN Cermet Coatings for Hybrid Metal Ceramic Bearing Systems
C. Bowman, V. Gorokhovsky (Arcomac Surface Engineering, LLC)
Manufacturers of advanced aircraft bearings face design requirements which entail severe loading conditions, high temperature operation, severe vibration and dithering modes, as well as corrosion attack from aggressive marine environments and fluorinated lubricants. Solutions to multifunctional design requirements of this nature are particularly suited to advanced surface engineered coating approaches. The Large Area Filtered Arc Deposition (LAFAD) process has demonstrated promising coatings and high deposition rates over large surface areas. In addition to the inherent advantages of conventional filtered arc technology (high hardness, improved adhesion, low density of pin-holes), the LAFAD technology allows functionally graded, multilayer, super-lattice and nanocomposite architectures of multi-elemental coatings via electro-magnetic mixing of two plasma flows composed of different metal vapor ion composition. In the present study, high temperature PFPAE lubricant corrosion performance testing was conducted on Pyrowear 675 coated with a dual segment multilayer TiCrN + BCN composite cermet coating, deposited by a combination of LAFAD and hybrid filtered-arc/UBM process. A special test rig was designed to simulate hybrid bearing (Pyrowear 675, Si@sub 3@N@sub 4@) operation at 340@super o@C, 3.2GPa contact, in the presence of PFPAE containing greases, for testing durations of 20hrs, 100hrs, and 200hrs. Corrosion performance results are presented for baseline uncoated and TiCrN + BCN coated Pyrowear 675 and characterized by a variety of methods including contact surface profilometry, SEM, EDS, and AES. The TiCrN + BCN coating demonstrated a near complete elimination of corrosion as compared to uncoated Pyrowear 675 which experienced severe corrosion over the general surface and rolling track. A discussion of the dual mechanical and corrosion requirements of the TiCr-TiCrN + BCN coating system and the further potential for optimization is included.
TS1-10 Double Glow Plasma Surface Copperized Burn-Resistant Titanium Alloy
P. Zhang, J. Tao, Z. Yao, Z. Xu (Nanjing University of Aeronautics and Astronautics, China)
Conventional titanium alloy may be ignited and burnt under high temperature, high pressure and high gas flow velocity condition. In order to avoid the 'titanium fire',burn-resistant alloying layers are made on the surface of Ti-6Al-4V and Ti-6.5Al-0.3Mo-1.5Zr-0.25Si titanium alloys by using double glow plasma surface alloying technology(DG Technology) . Ti-Cu binary burn-resistant alloy layer which thickness reaches to 150 µm has been made by DG plasma Copperizing. Burn-resistant properties are tested by laser ignition method using 2000W laser machine. the results show that the ignition temperature of alloyed layer with Cu concentration above 10% is higher about 300@super o@C than ignition temperature of Ti-6Al-4V and Ti-6.5Al-0.3Mo-1.5Zr-0.25Si substrates.