ICMCTF2004 Session AP: Symposium A Poster Session
Thursday, April 22, 2004 5:00 PM in Room San Diego
Thursday Afternoon
Time Period ThP Sessions | Topic A Sessions | Time Periods | Topics | ICMCTF2004 Schedule
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AP-1 Stabilization of ZrO2 PVD Coatings with Gd2O3
A. Portinha, V. Teixeira, J.O. Carneiro, M.F. Costa (Universidade do Minho, Portugal); N.P. Barradas, A.D. Sequeira (Instituto Tecnologico e Nuclear, Portugal) Zirconia coatings partially or full stabilized have many high temperatures applications (e.g. turbine blades, diesel engines, etc). However, to increase the efficiency of these systems and reduce their thermal conductivity a new kind of stabilizers are required. Gd2O3, among other rare earth oxides, is a potential candidate as dopant or as constituents together with the ZrO2Y2O3 system. The aim of the present paper is to study the influence of the Gd2O3 in the high-temperature phase stability of zirconia. Thin films of ZrO2Gd2O3 and ZrO2Y2O3Gd2O3 have been deposited by reactive DC magnetron sputtering with different dopant percentage and a wide range techniques have been used for their characterization. X-Ray Diffraction (XRD) was used for the structural characterization of the coatings, to study the influence of Gd2O3 addition on the high-temperature stabilized phases, and its influence on the microstructure and the level of stresses. Energy Dispersive X-ray Spectroscopy (EDX) and Rutherford Backscattering (RBS) were used to assess the coating composition. The mol % of Gd2O3 determined in the coatings are in the range of 2.1 to 17.5. The transition from the tetragonal to the cubic phase was clearly observed in the range of 5 to 6.5 mol % of dopant. Scanning Electron Microscopy (SEM) was used to determine the film thickness, to study the microstructure of the film in cross-section and also the surface morphology. The surface microtopography was analyzed by atomic force microscopy (AFM) and non destructive laser microtopography. The roughness of the coatings was evaluated and correlated with the optical parameters obtained by Optical Spectroscopy. A detailed description of the results and their discussion will be presented in the paper. |
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AP-2 Metal-plasma Ion Implanted Stainless Steel as Bipolar Plate Materials for Solid Polymer Fuel Cell
W.-Y. Ho, H.-J. Pan, J.J. Hwang (MingDao University, Taiwan, R.O.C.) Stainless steel is considered as a possible alternative material for bipolar plate in solid polymer fuel cell (SPFC). Because stainless steel bipolar plates are exposed to an operating environment with a pH of 2-3 at operating temperature less than 100°C, if not designed properly, dissolution or corrosion of metal substrate will occur. Specifically, when the metal plate is dissolved, the dissolved metal ions diffuse into the membrane and are trapped at ion exchange cites, resulting in a lowering ionic conductivity. In addition, a corrosion layer on the surface of a bipolar plate increases the electrical resistance in the corroded portion and decreases the output of the cell. Currently, metallic bipolar plates designed with protective layers such as carbon-based coating or metal-based nitrides are investigated as a possible alternative material for bipolar plate. The coating techniques for those coatings can be conducted using PVD or PECVD. However, researchers concluded that the coefficient of thermal expansion, corrosion resistance of coating, and micro-pores and micro-cracks play a vital role in protecting the bipolar plate from the hostile SPFC environment. Metal plasma ion implantation (MPII), a plasma-based surface technique, exhibits several advantages including enhancement of microstructure, wear resistance and corrosion resistance. It is concluded that the performance of the steels improves with the increase in the chromium content in the alloy. Stainless steels with high chromium content appear to be the best candidate stainless steel for a SPFC bipolar plate application. The aim of this work is to modify the surface properties of stainless steel material with high dose of Cr ions. The enhancement of corrosion resistance and electrical conductivity in the ion implantation treatment of stainless steel is anticipated. |
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AP-3 Electrochemical Performance of LBO-coated Spinel Lithium Manganese Oxide As Cathode Material for Li-ion Battery
H.W. Chan (National Tsing Hwa University, Taiwan, R.O.C.); J.G. Duh (National Tsing Hua University, Taiwan, R.O.C.) Surface treatments of the lithium manganese oxide cathode material coated by Lithium borate glass, Li2O-2B2O3, with excellent electrochemical cyclability and structural stability have been synthesized in this study. The lithium manganese oxide powder with different particle size, size distribution and morphology was calcined under various weight percent of LBO glass to form fine powder with single spinel phase. The surface area decreased with the content of the LBO glass. The average particle size was in the range of 3-8µm. Cyclic charge/discharge testing of the coin cells, fabricated by lithium manganese oxide and LBO-coated lithium manganese oxide as cathode material both provided high discharge capacity. Furthermore, the LBO-coated lithium manganese oxide powder showed better cycleability than the un-coated lithium manganese oxide after 20 cycles test. The LBO-coated lithium manganese oxide cathode material exhibited high discharge capacity and the fading rate was evidently decreased after cyclic test. |
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AP-4 Residual Stresses and Young's Modulus of Thermal Barrier Coatings Graded in Porosity
A. Portinha, V. Teixeira, J.O. Carneiro (Universidade do Minho, Portugal); M.G. Beghi, C.E. Bottani (Polytechnic of Milan, Italy); N. Franco (Nuclear and Technological Institute, Portugal); R. Vassen, D. Stoever (Forscchungszentrum Julich GmbH, Germany); A.D. Sequeira (Instituto Tecnologico e Nuclear, Portugal) Zirconia stabilized with 8 wt% Y2O3 is the most common material to be applied in thermal barrier coatings (TBC) owing to its excellent properties: low thermal conductivity; high toughness and low thermal expansion coefficient. Nevertheless, in order to increase the coatings lifetime, improvements in their thermo-mechanical behavior are still needed. With that purpose we propose in this paper a graded ceramic coating. These TBC have been produced by depositing a conventional NiCoCrAlY bond coat on a Inconel 738 LC substrate followed by an atmospheric plasma sprayed top coat of ZrO2-8wt%Y2O3 with a porosity gradient along the cross section. The aim of the present contribution is to study residual stresses and elastic properties of the coating as a function of the porosity gradient. For the characterization of the TBC's residual stresses we have used Raman and and X-ray diffraction (XRD) in different thermal conditions: as-sprayed; after thermal shock at 1000ºC, and annealing at 1100ºC in air during 100 hours. The top coatings show compressive stresses near the interface with the bond coat. A decrease of the stress level is observed along the cross section towards the surface. The residual stresses increase after annealing, however have smaller variations after thermal shock. The elastic properties were evaluated by Brillouin scattering: the scattering of laser light by acoustic waves in the GHz frequency range. The spectra at different depths indicate that in the annealed condition the acoustic velocity increases when approaching the external surface. The contact-less nature of Brillouin measurements also opens the way to the measurement of the elastic properties at high temperatures. |
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AP-5 Isothermal Oxidation of Al-Si DiffusionCoating Deposited by Arc-PVD on TiAlCrNb Alloy
L. Swadzba, G. Moskal, M. Hetmanczyk, M. Goral, B. Mendala (Silesian University of Technology, Poland); G. Jarczyk (ALD Vacuum Technologies GmbH, Germany) The excellent density specific properties of the γ-class of titanium aluminides make them attractive for temperature 600°C - 850°C aerospace applications. However titanium aluminides exhibit a strong TiO2 forming tendency rather than formation of the protective Al2O3 at high temperatures. For application at such temperature, an oxidation resistance coatings will likely be needed. The article presents research results of isothermal oxidation of TiAlCrNb intermetallic alloy with Al-Si protective coating and without coating. Protective coating were deposited by Arc-PVD method in two steps. In first the AlSi layer was deposited. In the second step the temperature of samples in vacuum chamber was increased and diffusion aluminides coating modified by Si was formed. After coating deposition the heat treatment of samples in vacuum was made. The temperature of heat treatment was 950°C and the time 2 hours. The isothermal oxidation tests were conducted at temperature 950°C. The test time was 200 hours. After 200h mass changes was registered. An analysis of the results obtained during oxidation test was performed. Phase composition, morphology and the distribution of elements were defined by EDX, XRD and SEM in AlSi layers as well as in the scale. |
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AP-6 Evaluation of Crucibles and Coatings in the Processing of Metallic Uranium
V.G. Vasconcelos, G., N.A.S. Rodrigues, V.H. Baggio-Scheid (Institute for Advanced Studies, Airspace Technical Center, Brazil); M.E. Sbampato (Institute for Advanced Studies, Airspace Technical Center); J.R. Martinelli (Instituto de Pesquisas Energeticas e Nucleares, Brazil) Metallic uranium is very reactive at the high temperatures used for its processing; therefore special refractory crucibles must be employed. The choice of these crucibles is based on their chemical inertia to the uranium sample. By minimizing the chemical attack, the amount of impurities in the molten material is reduced and the crucible lasts longer. This work presents a comparative study among coatings, that are used in the processing of metallic uranium, at a temperature above its melting point. In this work, samples of metallic uranium, without any superficial oxide layer, were placed on sample holders coated with alumina, magnesiun oxide and graphita coated with titaniun nitride and titanium nitride powder, and thermically treated in a vaccum furnace. The samples were kept at a certain temperature for determined time intervals and after that, cooled down to room temperature. Undesirable reactions of uranium or coatings with residual gases were minimized by heating the furnace only after pressure was reduced to approximately 10-4 Pa. Finally, the samples were removed from the furnace and prepared for characterization. This stage consisted in burnishing of selected surfaces and milling of the products of the reaction, originated from the interfaces. The possibility to contaminate the environment and the operator with uraniun, was minimized by mixing uranium powder with polyester resin. The size and the products of reaction were characterized as a function of temperature by using optic and electronic microscopy, EDS and X-ray diffraction. Although the alumina sample had shown higher activation energy than magnesia, it was corroded faster. On the other hand, the alumina could be protected by a thin film of titanium nitride, because no rection between titanium nitride and uraniun was observed even at 1700 K. |
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AP-7 Properties of WC:H Layer Obtained with Low Tungsten Concentration
R. Ruas (Brasimet Comercio e Industria SA, Brazil); D. Doerwald (Hauzer Techno Coating, The Netherlands); R.D. Mansano, A.P. Mousinho (Universidade de Sao Paulo, Brazil); R. Tietema (Hauzer Techno Coating BV, The Netherlands) In this work, reactive magnetron sputtering was used to deposit amorphous hydrogenated tungsten carbide films (WC:H). The targets used were Tungsten Carbide (WC) and Tungsten (W). In both cases different sputtering plasmas were created by varying of theirs parameters. The main parameters in these plasmas are RF power, process pressure and the gaseous composition (mixtures of argon and hydrocarbon gases. The layer obtained with different targets and plasma process shown changes in their properties. The layer deposited using the WC target and argon plasma is a soft layer, because of high concentration of W from the cathode. In deposition process using hydrocarbon and argon we obtain a hard layer of tungsten carbide, and its change with the increase a carbon contents in these plasmas. This change occurs because the rate of W sputtered using W cathode is too less compared to WC cathode. The small concentration of W in layer changes the kind of chemical bond in the layer. The kind of chemical bond should be change among sp2, sp3, single carbon and double carbon bond. In function of quantity and the kind of chemical bond, the proprieties of layer will be different, as such as, more hard or less, high or small stress, etc. The chemical analysis had been done using FTIR to analyze the quantity and kind of chemical bond of layer and RBS to analyze the composition of the layers. Using the hydrocarbon/argon plasmas were possible change the composition of this films and obtain a variation in the same sample layers of rich tungsten layer to layers of pure amorphous carbon. The roughness of layers obtained with W target is more less than layer obtained with WC cathode. The tribological proprieties will be change, but in both cases the layer have a high resistance to chemical attack. Hence we propose that W concentration is the most important to determine the properties of the WC:H layers. |
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AP-8 High Temperature Tribological Characterization of Zirconium Nitride Coatings
G. Lopez (Universidad de Oriente, Venezuela); M.H. Staia (Universidad Central de Venezuela) Coatings of Zirconium Nitride (ZrN) were deposited onto medium carbon steel (AISI 1045) substrate. The coatings were produced commercially by CFUMSIP. The unlubricated friction and wear behavior of coatings were evaluated at room temperature and during exposure to temperatures of 400 and 700°C, respectively. Adhesion, composite microhardness and other fundamental coating characteristics, such as thickness, surface morphology, microstructure and chemical composition were determined before and after exposure to the test temperature. Methods as the ball cratering, surface profilometry, scanning electron microscopy (SEM) and glow discharge optical spectroscopy (GDEOS) were used. The wear behavior was studied under a load of 2 N, using a ball-on-disc high temperature tribometer and sapphire balls (6mm diameter). Results indicated that the test temperature affected considerably the wear performance of ZrN coatings. The exposure of these coatings at high temperature caused an increase in the friction coefficient, and this increase was accompanied by a noticeable decrease in the composite hardness of the system coating-substrate. After the coating exposure at 700°C, delamination of the coatings occurred mainly due to the volume change, which took place as result of an intensive oxidation process of the unreactive titanium microdroplets particles, previously found in various parts of their surface. The SEM observations showed the presence of the coatings fracture and the lost of adhesion between the coating and the substrate. The best tribological performance was obtained for the coating tested at room temperature, which had the maximum composite Vickers hardness, presented the lowest friction and the highest Lc values. Results of the friction coefficients values, the wear volumes, debris composition of the heat exposed and unexposed samples are compared. The mechanisms of the wear process and adhesion failure at various test temperatures are explained. |
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AP-9 Design of Functional Composite Ceramic Coatings for Wood Fire Protection
J.O. Carneiro, V. Teixeira, F. Vaz, A. Portinha, P. Alpuim, M.F. Costa (Universidade do Minho, Portugal) This paper presents a technique and a material solution for wood fire protection. Wood has the major disadvantage of being combustible. However, this does not mean that wood construction is less safe than steel or even concrete construction. The burning of wood produces a charred layer on the surface of the material, which acts to insulate the unburned wood from the heat being radiated by the flames. Wood also has a very low thermal conductivity, which means that the inside of a wood member is little affected, while the outside surfaces burn. As with steel construction, wood floors and roof systems can acquire considerable fire resistance if the wood framing members are protected with a suitable insulating coating. Surface coating materials for engineering high temperature applications such as based oxide coatings MexOy are used for a variety of technological applications requiring thermal insulation, wear and erosion resistance or protection from oxidation and hot corrosion. Physical Vapor Deposition (PVD) techniques, an environment friendly deposition technique in particular reactive magnetron sputtering, is a suitable technology to deposit single layer and/or multilayered coatings using nanostructured material combination approaches. X-Ray diffraction (XRD), scanning electron microscopy (SEM) and non destructive laser micro-topography (LMT) will be used to characterise the coatings morphology and microstructure. The role of thin composite ceramic coatings in wood fire resistance will be studied in a qualitative way. For that, samples of bare wood and composite ceramic coated wood will be exposed to direct flame and the interval of time until burn will be compared. Moreover, both kinds of samples will be subjected to a four point static loading bend in order to study their "reserve" strength after fire exposure. |
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AP-10 Oxygen Effect on the Performance of Cr(N,O)/CrN Duplex Coatings for Injection Molding Applications
W.-Y. Ho (MIngDao University, Taiwan, R.O.C.); C.-H. Hsu, D.-H. Huang (Tatung University, Taiwan, R.O.C.) Plastics injection moulds are normally high-cost and quite complicated, consisting of many parts in relative motion to each other and to the plastics material. Abrasion, adhesion, corrosion, sticking, and fatigue are common operation problems, and several types of wear can be observed at the same time. Failure problems in the plastics injection molding industry can often be solved by an appropriate surface modification. Ion implantation, PVD, PECVD, plasma nitriding and combinations of these technologies can successfully improve the performance of molding parts. In our previous work, Cr2O3/CrN duplex coatings synthesized using cathodic arc deposition demonstrate better properties than CrN in relation to low frictional coefficient and oxidation resistance of 900°C in ambient atmosphere. Further study is the aim of this work. According to some reports, chromium oxynitride (Cr(N,O)) films should also have enhanced properties of wear resistance, corrosion resistance and chemical stability. In this work, we will report results of Cr(N,O) coatings using cathodic arc deposition and two reactive gases and a chromium target. The structures of coatings are designed as duplex coatings consisting of CrN interlayer and Cr(N,O) surface layer. The mechanical, corrosion properties as well as chemical composition of the Cr(N,O) films will be investigated with the varied oxygen and nitrogen reactive gas flow. |
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AP-11 Effect of the Sealing Treatment on the Corrosion Resistance of the Thermal Sprayed Ceramic Coatings
S. Liscano, L.E. Gil (National Polythecnic University, Venezuela); M.H. Staia (Venezuela Central University, Venezuela) Plasma sprayed ceramic coatings usually are characterized by a relatively high open porosity, which is deleterious when these coatings have to perform in an agressive environment. Various methods were applied to the as-deposited coatings in order to close this porosity and, hence, improve their corrosion resistance. In this study, plasma sprayed alumina+titanium oxides coatings were sealed using different sealants such as the phosphoric acid, phenolic and epoxy based sealants, all being applied by brushing them onto the surface of the as-deposited coating at atmospheric pressure. After the phosphoric acid impregnation, the specimens were heat treated for 2 hours at 100°C, 2 hours at 200°C and then for 2 hours at final curing temperature of 400° C. The corrosion resistance of the sealed coatings was evaluated in a 3.5% NaCl solution by conducting both electrochemical potentiodynamic polarization and linear polarization tests. The efectiveness of the sealing treatment was determined by relating the percentage of the open porosity, calculated from data obtained from the electrochemical measurements, the corrosion potential (Ecorr) and the corrosion current density (icorr) for each sealed coating. For comparison, results related to the unsealed coatings are also presented. The coatings before and after the corrosion tests were microstructural characterized employing standard tecniques as X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical microscopy (OM). The results obtained indicated that both the phenolic and epoxy sealants resulted to be more effective than the phosphoric acid in enhancing the corrosion resistance of the thermally sprayed ceramic coatings used in the present research. |
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AP-12 Electrochemicals Corrosion Tests and HRTEM Molecular Simulation Techniques of an AISI-SAE 4140 Steel Nitrided for Post-discharge Microwave Plasma.
A. Medina-Flores (UMSNH Instituto de Investigaciones Metalurgicas, Mexico); P. Santiago (Instituto Nacional de Investigaciones Nucleares, Mexico); J. Ascencio (Instituto Mexicano del Petroleo, Mexico); J. Oseguera (ITESM, Mexico) An AISI-SAE 4140 low alloy steel was nitrided in post-discharge microwave conditions at 540°C during 3 hrs. The microstructure and composition of the nitrided layer were analyzed. The corrosion resistance of the untreated and nitrided samples was compared in several electrochemical corrosion tests such as tafel test, polarization resistance, polarization anodic, cyclic polarization and electrochemical noise in a chloride environment. The resistance to corrosion was evaluated under potentiostatic control at anodic and cathodic potentials. The untreated and nitrided pieces were characterized by X-Ray Diffraction (XRD) to identify the crystalline phases, Scanning Electron Microscopy (SEM) was used to examine the morphology and thickness of the nitride layer, which in average was around 12m. |
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AP-13 Development and Testing of Ceramic Thermal Barrier Coatings
D. Zhu, S.R. Choi, R.A. Miller (NASA Glenn Research Center) Ceramic thermal barrier coatings will play an increasingly important role in future gas turbine engines because of their ability to effectively protect the engine components and further raise engine temperatures. Durability of the coating systems remains a critical issue with the ever-increasing temperature requirements. Thermal conductivity increase and coating degradation due to sintering and phase changes are known to be detrimental to coating performance. There is a need to characterize the coating behavior and temperature limits, in order to potentially take full advantage of the current coating capability, and also accurately assess the benefit gained from advanced coating development. In this study, thermal conductivity behavior and cyclic durability of plasma-sprayed ZrO2-8wt%Y2O3 thermal barrier coatings were evaluated under laser heat-flux simulated high temperature, large thermal gradient and thermal cycling conditions. The coating degradation and failure processes were assessed by real-time monitoring of the coating thermal conductivity under the test conditions. The ceramic coating crack propagation driving forces and resulting failure modes will be discussed in light of high temperature mechanical fatigue and fracture testing results. |
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AP-14 High-Temperature Diffusion Barriers for Ni-base Superalloys
J.A. Haynes (Oak Ridge National Laboratory); Y. Zhang (Tennessee Technological University); K.S. Reeves, K.M. Cooley, B.A. Pint (Oak Ridge National Laboratory) Oxidation-resistant metallic bond coatings are degraded by loss of aluminum due to both oxidation and interdiffusion with the underlying superalloy substrate. An effective diffusion barrier between the superalloy and bond coating would reduce the amount of Al that is lost to the substrate by interdiffusion and would limit the amount of substrate elements (such as Cr, Re, Ta, W) that diffuse into the coating to degrade its corrosion and oxidation resistance and reduce the life of thermal barrier coatings. In this preliminary study, various materials and compounds (including Hf and Pt-Hf) were evaluated as potential high-temperature diffusion barriers. Candidate materials were sputter deposited onto single-crystal superalloy coupons, followed by various heat treatments with the goal of forming intermetallic compounds, such as Engel-Brewer-type compounds, which are known to have unusual thermodynamic stability. The coupons were subsequently aluminized to form nickel aluminide or nickel platinum aluminide coatings, which were isothermally and cyclicly oxidized at 1050°-1150°C. Coatings were characterized via secondary electron microscopy and electron microprobe analysis. Research sponsored by the Distributed Energy Resources Program, U. S. Department of Energy, under contract DE-AC05-00OR22725 with UT-Battelle, LLC. |