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ICMCTF2009 Session AP: Symposium A Poster Session

Thursday, April 30, 2009 5:00 PM in Room Town & Country

Thursday Afternoon

Time Period ThP Sessions | Topic A Sessions | Time Periods | Topics | ICMCTF2009 Schedule

AP-1 Hard Protective Si-Zr-O Coatings Resistant to Thermal Cycling in Air up to 1400°C J. Musil, V. Satava, P. Zeman, R. Cerstvy (University of West Bohemia, Czech Republic) The article reports on structure, mechanical properties and oxidation resistance of 7000 nm thick Si-Zr-O film reactively sputtered using a closed magnetic field dual magnetron system operated in ac pulse mode. The films were sputtered from a composed target. Main attention is devoted to the investigation of the effect of the structure of film on the thermal stability of its mechanical properties and oxidation resistance. It was found that (1) the Si₃₁Zr₅O₆₄ film sputtered at the substrate temperature T_s=500°C is amorphous, (2) the Si₃₁Zr₅O₆₄ film is sputtered at high deposition rate a_D=100 nm/min, (3) the structure of Si₃₁Zr₅O₆₄ film gradually changes during thermal annealing in air from the amorphous to the polycrystalline with t-ZrO₂ phase, (4) the t-ZrO₂ phase is stable in wide range of T_a up to 1550°C and no conversion of the t-ZrO₂ phase into m-ZrO₂ phas e is observed during subsequent cooling from 1550°C down to room temperature RT, (5) the hardness H and effective Young s modulus E* of Si₃₁Zr₅O₆₄ film are thermally stable and resistant to the oxidation in flowing air during thermal cycling from room temperature (RT) up to 1400°C for 4 hours with T_a=1000°C and (6) the Si₃₁Zr₅O₆₄ film converts into a surface layer composed of a mixture of t-ZrO₂+m-ZrO₂+Al₆Si₂O₁₃+SiO₂ phases at annealing temperatures T_a=1550°C due to its strong interaction with the Al₂O₃ substrate. Main issue of this investigation is the finding that the properties of protective coating do not change during thermal cycling as far the structure of the coating is unchanged during increasing and decreasing of the annealing temperature T_a.
AP-4 Analysis of Hf-Rich Precipitates in NiAl-Hf Bond Coats via Transmission Electron Microscopy and Atom Probe Tomography M.A. Bestor, M.S. Kirsch, R.L. Martens, M.L. Weaver (The University of Alabama) It has been reported that NiAl-based bond overlay coatings with concentrations of reactive elements (e.g. Hf and Zr) in excess of their solubility limits can exhibit oxidation resistance comparable to state-of-the-art platinum aluminides. In this study, a microstructural investigation was conducted using atom probe tomography (ATP) and transmission electron microscopy of precipitation/dispersion strengthened NiAl-Hf bond overlay coatings deposited using DC magnetron sputtering onto a single crystal Ni-based superalloy. Post-deposition annealing of NiAl-1.0 at% Hf coatings at 1000°C for one to four hours produced nanometer-sized Hf-rich precipitates. Longer pre-oxidation annealing times resulted in smaller mass gains during isothermal oxidation with values approaching those of model NiAl-0.05 at.% Hf coating alloys. It is believed that the precipitates improve the oxidation performance of these coatings by inhibiting the inward diffusion of oxygen and the upward diffusion of aluminum. High angle annular dark field (HAADF) images showed that the Hf segregates to the grain boundaries and also forms precipitates after annealing. APT determined that the precipitates were disk-shaped, Hf-rich, and that carbon localizes with the precipitates. Results suggest that suitable oxidation resistance can be obtained in “over-doped” alloys by optimizing the coating chemistry, grain structure and precipitate distribution.
AP-5 Properties of the Thermally Stable Si-B-C-N Coatings Prepared by Reactive dc Magnetron Co-Sputtering P. Calta, J. Capek, P. Zeman, P. Steidl, R. Cerstvy, J. Vlcek (University of West Bohemia, Czech Republic) Novel quaternary Si-B-C-N materials are becoming increasingly attractive because of their possible high-temperature and harsh-environment applications. In our previous investigation, the Si-B-C-N coatings were prepared by reactive dc magnetron co-sputtering using a single C-Si-B or B₄C-Si target in nitrogen-argon gas mixtures at an rf induced negative substrate bias voltage and the substrate temperature T_s = 350°C kept by an Ohmic heater. In this work, the Si-B-C-N coatings were deposited using the B₄C-Si target with a fixed 75% Si fraction in the target erosion area on floating Si, SiC, Cu and glass substrates (U_f = -20 to -40 V) without an additional heating (T_s = 180 – 250°C), i. e., under simplified experimental conditions. The total pressure of the N₂-Ar gas mixture of 0.5 Pa and the discharge current on the magnetron target of 1 A were held constant. The effect of the gas mixture composition on mechanical, optical and electrical properties of the coatings, and their high-temperature oxidation resistance and thermal stability in inert gases (He and Ar) were investigated. The coatings, typically 2 µm thick, were found to be amorphous with high hardness (around 21 Gpa) and low compressive stress (approximately 0.5 Gpa). With the increasing Ar fraction in the gas mixture, their optical transparency decreases while their electrical conductivity raises (up to 5 Sm^-1). The coatings prepared with a 50% Ar fraction exhibited very high oxidation resistance in air up to 1500°C and extremely high thermal stability in the inert gases up to 1600°C.
AP-6 Growth of Intermetallic Layer in the Aluminide Mild Steel During Hot-dipping W.-J. Cheng, C.-J. Wang (National Taiwan University of Science and Technology, Taiwan) Mild steel was coated by hot-dipping into a molten aluminum bath. The growth behavior in the intermetallic layer during hot-dip process at 750°C was analyzed by Electron Backscatter Diffraction (EBSD). The results showed that the aluminide layer consisted of an outer aluminum topcoat, minor FeAl₃ and major Fe₂Al₅, respectively. Besides, Fe₂Al₅ possessed a tongue-like morphology, which caused the corresponding serration-like morphology of the steel substrate. The interface of the Fe₂Al₅ phase after removed the steel substrate displayed a columnar structure growing toward the steel substrate, implying that Fe₂Al₅ grew with a rapid rate along the diffusion direction. Moreover, the EBSD results revealed the Fe₂Al₅ phase not only composed of columnar grains, but also possessed fine grains clustered around the peaks of the serration-like steel substrate.
AP-7 Control of Coating Thickness Ratio for Optimizing Adhesive Strength and Thermal Shock Resistance in Air-Plasma Sprayed Zirconia Based Thermal Barrier Coatings Y.G. Jung, S.I. Jung, Y.S. Sim, J.Y. Kwon, J.H. Lee, U. Paik (Changwon national University, Korea) The effects of thickness ratio between top and bond coats on adhesive strength and thermal shock resistance have been investigated under thermal fatigue in thermal barrier coating (TBC) systems prepared using an air-plasma spray (APS) process. The thermal fatigue tests were conducted at T = 1,100°C for fully impeded tests into a furnace and at T = 1,210°C for one-side exposed tests, with dwell times of 8 and 24 h. In the as-prepared TBC systems, as the top coat thickness is increased, the adhesive strength is decreased, showing the fracture origin at inside of top coat. Relatively long-term cyclic thermal fatigue of 24 h easily delaminate the top coat rather than that of 8 h, and the tests impeded into the furnace pursue the delamination or fracture of the top coat. The thermal fatigue before delamination in both thermal exposure methods increases the adhesive strength in both cases, while the one-side exposed sample extends the thermal cycling lifetime. E ven though the thickness ratio is same, the thicker top coat shows better thermal shock resistance than thinner one. The optimum thickness ratio between bond and top coats is 1:2 for improving and enhancing the adhesive strength and the thermal shock resistance, respectively. The thermally grown oxide (TGO) layer thickness is not much affected by the top coat thickness, showing a nominal thickness of 8 μm after delamination in both thermal exposure methods. The effects of the thermal fatigue condition on microstructural evolution, mechanical properties, and thermal shock resistance are discussed.
AP-8 Diffusion Aluminide Coatings for TiAl Intermetallic Turbine Blades M. Goral, L. Swadzba, G.J. Moskal (The Silesian University of Technology, Poland); G. Jarczyk (ALD Vacuum Technologies AG, Germany) Alloys based on the intermetallic phases from Ti-Al system are materials which, on the base of their resistance characteristics, could be widely used in automotive and aerospace applications. The main restriction of the usage of those materials is their still insufficient oxidation resistance above 850°C. This parameters might be improved using aluminide coatings containing TiAl₂and TiAl₃phases, which induces the creation of Al₂O₃scale (possessing much better protective attributes) in oxidation process. This type of aluminides can be deposited on the surface of TiAl alloys by different methods such as pack cementation, plasma spraying or magnetron sputtering. This article presents a new method of production of aluminide coatings using out of pack technology. The investigated coating has been produced on turbine blades made from Ti47Al5Nb intermetallic alloy. The surface morphology, structure and phase and chemical composition has been in vestigated using XRD phase analysis, SEM and EPMA. The phase analysis showed that TiAl₂is main component of deposited coating. The oxidation resistance of coating has been also investigated. Isothermal oxidation test of TiAl turbine blades was conducted. After 600h test at 950°C oxidation test the spallation of scale from the surface of turbine blades without coating was observed. The scale on the turbine blade with aluminide coatings was very thin and spallation was not presented. The gas phase aluminizing technology can be applied in aerospace industry It is very attractive technology for improving of oxidation resistance of turbine blades.
AP-9 Dry Drilling of Austempered Ductile Iron (ADI) with Different Coated Drill W. Mattes (SENAI-SC, ALVES, Brazil); S. Martins (SOCIESC, Brazil) Due to economic and environmental reasons, dry drilling research have been developed attending the global marketing necessities. However, long tool life and high quality of holes are not easy obtained in dry conditions. Nowadays, many coatings have been developed in order to aid the machining process. Thus, the aim of this work is to evaluate which coating type can improve the dry drilling performance of ADI. Dry drilling tests were carried out with Austempered Ductile Iron (ADI) with 293 hardness Brinell. Carbide drills with different coatings were used as cut tool. The drilling parameter were cut speed of 120m/min, rate feed of 0.2mm and hole depth of 30mm. Three coatings were tested: AlCr, TiAlN and one combination of TiAlN and AlCrN. Based on these results, the better performance of dry drilling of ADI was achieved when TiAlN+ AlCrN coating was used. So, with adequate coating choose it is possible to improve the dry drilling process.
AP-10 The Oxidation of a Air Plasma Sprayed Thermal Barrier Coating P. Smith, R.G. Wellman (Cranfield University, United Kingdom); R. Jones, M. Wybrow (Rolls Royce, United Kingdom); J.R. Nicholls (Cranfield University, United Kingdom) Since the development of air plasma sprayed (APS) thermal barrier coatings (TBC) and their application in hot oxidising conditions, oxidation has become a key element in understanding coating degradation and eventual failure. The operating conditions of a TBC can be partly recreated using isothermal and cyclic furnaces to replicate the in-service oxidation of a TBC system. The main aim of this project was to study the changing morphology and growth of the thermally grown oxide (TGO) in an APS TBC system, using scanning electron microscopy and energy dispersive x-ray analysis. To do this it was necessary to obtain samples at different stages of oxidation. The samples of the APS TBC were thermally cycled at 1100°C and taken out at increasing time intervals to be analysed. The TGO thickness was measured to obtain the rate of oxidation and to determine the type of oxides present at various stages. The analysis of the TGO shows the initial growth of an alumina layer during the early stages of thermal cycling, however, after further cycling areas of a mixed oxide appear between the alumina and yttria stabilised zirconia (YSZ). At the point of coating failure the mixed oxide has grown to form a continuous layer. The growth rates of both oxide layers were recorded to observe how the mixed oxide interacts with the alumina layer, where the mixed oxide most frequently occurs, due to the undulating morphology at the bond coat-TGO-YSZ interfaces, and to determine the origin of the mixed oxide.
AP-11 Influence of Deposition Parameters on Structure and Oxidation Resistance of Diffusion Aluminide Coatings Obtained by CVD Method on Ni-Base Superalloys L. Swadzba, B. Mendala, M. Hetmanczyk, B. Witala, M. Goral (The Silesian University of Technology, Poland) Chemical vapour deposition (CVD) method plays meaningful role in depositon aluminide coatings on nickel based superalloys. Thank to this method it is possible to deposit aluminide coatings in cooling channels which is difficult using other methods. In this paper result of development and properties of high-temperature coating deposited on superalloys such as single crystal PWA 1484 and polycrystalline Mar M-247, Inconel 100 will be presented. Result of diffusion aluminizing using high-tech ION BOND equipment and “out of pack” equipment will be showed. There will be shown influence of technological parameters such as: temperature, pressure in retort, chemical composition of reactant gases on microstructure, thickness and phase composition of aluminide coatings. Low activity coating of NiAl type containing 20 – 25% mas. and 30µm thickness was developed. Thickness of layer and content of aluminium in coating on the surface is insufficient to fully protect bas e material. Further processes were conduct with using additional source granuls of chemical composition of Ni, Al, Cr and modified by reactive elements. As a result high activity aluminide coatings type of NiAl were developed. Aluminide coatings were investigated by light microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray diffraction analysis (XRD). Result of 23 hour oxidation resistance test of aluminide coatings will be presented. There will be shown influence of chemical composition 3 different nickel based superalloys on properties of aluminide coatings.
AP-12 Characterization of Microstructure and Properties of Plasma Sprayed Ceramic Coatings on Mg Alloys A. Iwaniak, G.J. Moskal, A. Kiebus, T. Rzychon (The Silesian University of Technology, Poland) This article will be presents results of microstructural investigation and properties characterization of ceramic cotings deposited on magnesium alloy by plasma spraying. The study has been done on AZ91 type alloy with ceramic top coat on the basis of tungsten carbides and NiCr bond coat. First of investigated area is related to quantitative and qualitative description of ceramic top surface, bond coat and magnesium alloy substrate. Second area of investigations is connected to XRD characterization of deposited coating. The purpose of this research was identification of the residual stress in the top coat. Another subject is related to microstructural characterization of coating from their quality point of view. The parameters which identify the quality of the bond coat and the ceramic coating consist: the thickness of the layers; the quality of the connection between the metal base and the bond coat; the presence of cracks and oxides; porosity; globular grains; bond c oat integrity; the roughness of the bond-coat surface; the microstructure of the ceramic layer – the analysis involves the porosity assessment, randomly oriented cracking and their shape, metallic impurities and globular grains.
AP-13 High Temperature Wear Behaviour of Aluminum Oxide Coatings Produced by Ac Micro Arc Oxidation E. Arslan, Y. Totik, Y. Vangolu, A. Alsaran, I. Efeoglu (Ataturk University, Turkey) Aluminum alloys are becoming increasingly important, especially in the automotive and aerospace industries. However, these materials tend to have poor wear resistance at atmospheric and high temperature conditions. Aluminum oxide coatings are potentially very effective in developing hard, wear-resistant surfaces. The aim of this present study was to evaluate the high temperature wear behavior of aluminum oxide coatings at different temperatures by using high temperature pin-on-disc tribotester and alumina balls as counterfaces. The aluminum oxide coatings were produced by AC micro arc oxidation (MAO). The structural analyses of the coatings were performed using XRD and SEM techniques. The hardness was measured using microhardness tester. Keyword: Aluminum alloys, Plasma electrolytic oxidation, High temperature, Wear.
AP-14 Thermal Barrier Coatings by Electron Beam-Hysical Vapor Deposition of Zirconia Co-Doped with Yttria and Niobia D.S. Almeida, C.A.A. Cairo (Centro Tecnologico de Aeronautica, Brazil); D.A.P. Reis (Instituto Tecnologico de Aeronautica, Brazil); V. Henriques, F. Piorino Neto (Centro Tecnologico de Aeronautica, Brazil) The most usual ceramic material for coating turbine blades is yttria doped zirconia. Addition of niobia, as a co-dopant in the Y₂O₃-ZrO₂ system, can reduce the thermal conductivity and improve mechanical properties of the coating. The purpose of this work is to evaluate the influence of the addition of niobia on the microstructure and thermal properties of the ceramic coatings. SEM on coatings fractured cross-section shows a columnar structure and the results of XRD show only zirconia tetragonal phase in the ceramic coating for the chemical composition range studied. As the difference NbO_2.5-YO_1.5 mol percent increases, the tetragonality increases. A significant reduction of the thermal conductivity, measured by laser flash technique, in the zirconia coating codoped with yttria and niobia when compared with zirconia-yttria coating was observed.
AP-15 Effects of Granulometry on Properties of Plasma Sprayed Yttria-Stabilized Zirconia Coatings S. Liscano, L. Gil (UNEXPO, Venezuela); M.H. Staia (Universidad Central de Venezuela); O. León (UNEXPO, Venezuela) It is well known that the quality and properties of the plasma-sprayed coatings are strongly dependent on the coating microstructures, and this of in-flight particle characteristics and processing parameters. The aim of this work was to determine the influence of granulometry of feedstock powders on porosity and mechanical properties of plasma sprayed YSZ TBCs. NiAl bond coats were deposited on a number of AISI 310 specimens using HVOF spray technique. Furthermore, these specimens were coated, with ZrO₂–8%Y₂O₃ powders with two different granulometry, using air plasma spray technique (APS). Duplex coatings were then characterized using optical microscope, Scanning Electron Microscopy (SEM) coupled with energy dispersive X-ray analysis (EDS), and X-ray Diffraction (XRD). The fracture toughness of these coatings was evaluated using micro-indentation techniques. The results show that as sprayed microstructure is typically porous, and it was evidenced that t he porosity increased with particle size, and this was associated with an increased of partially melted particles, which was directly related to increase of fracture toughness. Cracks were found to initiate and propagate easily in direction parallel to the coating growth directions than along the splat boundaries. EDS analyses revealed that oxidation of aluminum, in the NiAl alloy, occur in the high-temperature plasma-spray stream during deposition.
AP-16 Effect of Hf Alloy Addition on Aluminide Coating Performance B.A. Pint, K.L. More, J.A. Haynes (Oak Ridge National Laboratory) Additions of Hf were made to a conventional Ni-base chromia-forming alloy and an alumina-forming austenitic alloy to improve their high temperature oxidation resistance after aluminizing. The addition of Hf is intended to improve the adhesion of thermally grown alumina on the coating thereby improving oxidation resistance. Coatings were made by a standard low activity chemical vapor deposition process at 1100°C and produced microstructures typical of NiAl coatings. Oxidation resistance is being assessed using thermal cycling at 1100°-1150°C. Adding Hf as an alloy addition to the substrate is one means of incorporating Hf into a simple aluminide coating and is being used to assess the potential performance benefit of adding Hf by a conventional aluminizing process.

Time Period ThP Sessions | Topic A Sessions | Time Periods | Topics | ICMCTF2009 Schedule