ICMCTF2008 Session AP: Symposium A Poster Session
Thursday, May 1, 2008 5:00 PM in Room Town & Country
Thursday Afternoon
Time Period ThP Sessions | Topic A Sessions | Time Periods | Topics | ICMCTF2008 Schedule
|
AP-2 Electrochemical Impedance Spectroscopy (EIS) Study of Al2O3/YSZ Nanostructured Thermal Barrier Coatings (TBC)
C. Amaya, W. Aperador, J.C. Caicedo, G. Zambrano, P. Prieto (Universidad del Valle, Colombia) Stainless steels with high content of Ni and Cr, have a limited use in aerospace industries, since over 650°C are susceptible to corrosion. In order to improve this issue, a Thermal Barrier Coatings (TBC) of ZrO2-8% mol Y2O3(8YSZ) were deposited onto AISI 304 stainless steel substrates by r.f (13.56 MHz) multi-target magnetron sputtering. A buffer layer of Al2O3was incorporated to improve adhesion of YSZ monolayer to the substrate. The influence of the Al2O3/YSZ coating on the electrochemical conductance CTtand the corrosion evolution when the steels are exposed at temperatures of 700 and 500°C for 2, 4 and 6h, was examined. Electrochemical Impedance Spectroscopy (EIS) measurements indicated that electrochemical conductance CTtdiminished from 3.7x10-3to 1.2x10-6Siemens and the corrosion velocity was reduced from 53.4 to 6.8 mpy, when the AISI 304 stainless steel was covered with the Al2O3/YSZ coatings. An opposite behavior was observed after annealing at 500 and 700°C for 2, 4 and 6 hours. The electrochemical conductance CTtat 700°C after 6 hours of exposure was one order of magnitude lower (4.8 x 10-4Simens) than for the AISI 304 stainless steel without Al2O3/YSZ thermal barrier coatings. This behavior of CTtcan be correlated with the thermal conductivity of these nanostructured TBC, deposited in our conditions and determinates by other techniques. Acknowledgements: This work was supported by COLCIENCIAS, and by the Excellence Center for Novel Materials, CENM, under the RC-043-2005 contract. |
|
AP-3 Effect of the Gas Mixture Composition on High-Temperature Behavior of Magnetron Sputtered Si-B-C-N Coatings
J. Capek, S. Hreben, P. Zeman, J. Vlcek, R. Cerstvy (University of West Bohemia, Czech Republic) Our preliminary investigation of oxidation resistance and thermal stability of the Si-B-C-N coatings to 1300 °C has indicated a strong effect of the gas mixture composition on coating properties. From this reason, further tests were carried out to investigate the high-temperature behavior of these coatings up to 1700 °C. The Si-B-C-N coatings (typically 2-3 µm thick) were deposited on Si, SiC and Cu substrates by dc magnetron co-sputtering using a single B4C -Si target in nitrogen-argon gas mixture. The effect of the gas mixture composition (50 or 75 % of Ar) on the high-temperature behavior of the Si-B-C-N coatings was investigated using a symmetrical high-resolution Setaram TAG 2400 thermogravimetric system and differential scanning calorimeter DSC Labsys 1600 in a synthetic air and in an inert gas (He, Ar). The elemental composition of the coatings was determined by Rutherford back-scattering spectrometry (Si, B, C, N, O, Ar) and elastic recoil detection method (H). The structure of the coatings was measured by XRD. The gas mixture composition was found to be a very important process parameter having a great impact on the elemental composition (especially on the N/Si ratio) and consequently on final properties of the Si-B-C-N coatings, such as oxidation resistance and thermal stability of their structure and mechanical properties. The coatings sputtered at a 50 % Ar fraction in the gas mixture exhibited extremely high oxidation resistance up to 1500°C and preservation of the amorphous state even up to 1700 °C in air. No mass or structural changes of the coatings were also detected by TG and DSC analyses up to 1600°C in an inert gas. |
|
AP-4 Effects of Si/Ta and Nitrogen Ratios on the Thermal Stability of Ta-Si-N Thin Films by Magnetron Reactive Cosputtering
C.K. Chung, T.S. Chen, B.H. Wu, A. Nautiyal (National Cheng Kung University, Taiwan) Ta-Si-N thin films prepared by different nitrogen ratio and Si/Ta power ratio were performed using magnetron reactive cosputtering from separate Ta and Si targets in an argon and nitrogen atmosphere. Both high-vacuum furnace annealing (FA) and vacuum rapid thermal annealing (RTA) were used to investigate the thermal stability of different nanostructured Ta-Si-N films. The relationship between the microstructure, morphology, electrical, mechanical properties and thermal stability of the Ta-Si-N thin films were characterized by grazing incident X-ray diffractometer, scanning electron microscope four-point probe method and nanoindentation, respectively. As the silicon atoms were added in the polycrystalline Ta-N to form Ta-Si-N films, the microstructure of Ta-Si-N films becomes amorphous-like structure. The high Si/Ta power ratio and low nitrogen ration will increase the degree of amorphization as well as smaller nanocrystalline grains in the deposited films. Both amorphous-like and polycrystalline Ta-Si-N films could endure temperature up to 900°C for 1 h under FA at higher vacuum of 5 x 10-5 Torr while the their phase and morphology had been changed at 750-900°C for 1 min under RTA at higher pressure of 2 x 10-2 Torr. The thermal stability of Ta-Si-N films increases with the Si/Ta ratio and magnitude of vacuum. |
|
AP-5 High-Temperature Activation of Adaptive Surfaces: Sharkskin and Self-Cleaning
P. Schaaf, S. Cusenza (University of Göttingen, Germany); V. Drescher, J. Wilden (Technical University of Ilmenau, Germany) Embedding ceramic particles with a negative thermal expansion coefficient (NEC) into a metallic corrosion resistant coating can establish a reversible thermal activation of a defined surface microstructure with the aim of having a sharkskin at high temperatures (in use) and a self-cleaning (Lotus effect) at low temperatures (out of use). For that, MCrAlY alloy is intermixed with yttrium and tungsten oxide as powder and then deposited onto a substrate. This coating is then implanted with oxygen and/or yttrium ions in order to incubate the formation of Y2W3O12 which is a ceramic with a strong NEC. Such prepared coatings are then exposed to high temperature and the effects on phase formation and morphology changes are investigated in detail at high temperatures and afterwards at room temperature in detail. Results of phase formation, surface micro-morphology, microstructure and properties of the coatings are presented. |
|
AP-6 Degradation of Hot-Dipping Al-Si Coating on Nickel-Base Superalloy Inconel 718 at 1100°C
S.-M. Chen, C.-J. Wang, W.-J. Cheng (National Taiwan University of Science and Technology, Taiwan) Ni-base superalloy Inconel 718 was coated by hot-dipping into a molten bath containing Al-10wt.%Si. The high temperature oxidation behavior of aluminide coating and its phase transformation were studied at 1100°C in static air. After hot-dip treatment, the coating layer consisted of two layers, the outer layer being Al and the inner layer being FeAlSi. The results of a high-temperature oxidation test showed a dense α-Al2O3 oxide layer on the aluminide coating surface. The aluminide coating mainly consists of an outer aluminide layer and an interdiffusion zone. The primary phase of the aluminide layer is NiAl with Cr3Si particles. The interdiffusion zone is composed of σ phase with white particles of Cr37Nb27Si36. Even though, the inward diffusion of Al in the aluminide layer was restricted by the interdiffusion zone. With time increasing, the aluminide layer which was also gradually transformed to Al alloyed γ-substrate phase due to the interdiffusion reaction at high temperature. Afterwards, loss of protection behavior from the coating layer occurred only by Al-free oxides such as Nb0.6Cr0.4O2 and NbO2 formed on the coating specimen exposed at 1100°C for 2040 h. |
|
AP-7 Effect of Chromate Passivation Treatments on the Structure, Morphology and Corrosion Properties of IVD Aluminium and Zinc-Based Coatings on Mild Steel.
N. Alanazi, Z.M. Rosli, A. Leyland, A. Matthews (University of Sheffield, United Kingdom) Chromate conversion coatings are still one of the most efficient surface post-treatments for zinc Galvanized and aluminium Ivadized steel. The performance of the complete system depends strongly on the composition and structure of the chromate layer, which is normally characterised by destructive methods. The main purpose of this paper is to study the effect of chromate passivation treatments on the structure, morphology and corrosion properties of electroplated zinc and IVD aluminium coatings on mild steel. Open circuit potential, polarization curves and electrochemical impedance spectroscopy (EIS) are used to investigate corrosion behaviour. A small, but significant, corrosion potential increase (around 46 mV) of yellow (Cr+6) passivation coating compared to unpassivated Zn plate and clear (Cr+3) passivation was observed. Among three different techniques, EIS was the most sensitive and reliable. Atomic force microscopy was used to gain insights into the morphology of the surface treatments evaluated and to study the size and depth of cracks seen in chromate coatings. Surface morphology, film thickness and composition were observed by SEM (JEOL JSM-6400) and EDS. X-ray diffraction (Siemens D5000) was also used (in both θ/2θ and glancing-angle modes) to identify the coating phases. |
|
AP-8 Deposition of Silicon Enriched Nickel Aluminide Coatings on Internally Cooled Airfoils
J. Kohlscheen, H.R. Stock (Stiftung Institut für Werkstofftechnik, Germany) Aluminum diffusion coatings enriched with silicon were prepared by chemical vapor deposition on various nickel-based materials such as almost pure nickel and Rene80. Aluminum and silicon chloride served as precursors. They were generated in-situ by feeding gaseous hydrogen chloride (HCl) into a heated reactive chamber (1100°C) which contained aluminum and silicon donating material. An excess of hydrogen gas flow was found to improve the coating growth rate. Due to the high reactivity of aluminum, high ratios of silicon to aluminum donator had to be maintained (at least 10 : 1). The coating thickness was determined from glow discharge spectroscopy and metallographic cross sections. Silicon contents of up to 20 at. % could be achieved. Hot corrosion testing in sulfur containing air showed that an increasing silicon content in the layers yielded a higher resistance to corrosive attack. By pressure variation during the coating process the coating of internal cooling channels could be improved. This is explained by frequent exchange of reactive gas in the interior of the airfoils. |
|
AP-9 Anti-Oxidation Properties of (Ti,Al)N Films Prepared by DC Reactive Magnetron Sputtering and Mechanism
T. Zhou, P.L. Nie, X. Cai (Shanghai Jiao Tong University, China); P.K. Chu, M. Xu, R. Fu (City University of Hong Kong) TiN films are widely used in coatings on cutting and forming tools due to their high hardness and good wear resistance. However, the service life of tools protected by TiN films depends not only on the mechanical properties of the TiN films such as hardness and wear resistance, but also on the oxidation resistance of the films because oxidized TiN films have relatively poor mechanical properties compared to unoxidized TiN films and are inclined to spalling from the substrate under loading. In high temperature applications, for instance at temperatures exceeding 773 K, TiN films can be easily oxidized forming rutile TiO2. Hence, it is necessary to improve both the mechanical and anti-oxidation properties of TiN films. The addition of a third element X such as Al, Si, Cr, Zr to the TiN matrix to form a ternary compound (Ti,X)N is a viable approach. Of the various ternary compounds, (Ti,Al)N has the best mechanical and anti-oxidation properties. The most common method to produce the materials is physical vapor deposition (PVD) which requires an alloy target or dual sources. In order to better control the composition of the ternary compound film, DC reactive magnetron sputtering using a compound target is used in this work. The compound target is prepared by embedding Al blocks in the Ti substrate, and by varying the ratio of the Al block to Ti substrate and processing parameters such as N2 partial pressure, bias voltage, and sputtering current, (Ti,Al)N films with different compositions can be deposited on 316 stainless steel substrates to investigate the anti-oxidation properties and roles of Al. The anti-oxidation properties are investigated by thermogravimetric analysis (TGA) and the microstructures and phases of the oxide layers are determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). According to the TGA results, the (Ti,Al)N films prepared by our method possess significantly better anti-oxidation properties than TiN films at elevated temperatures (from 873 K to 1073 K) in air. When TiN is oxidized at 873 K for 5h, the oxide layer on TiN is not continuous and spalling is observed whereas thermal oxidation of (Ti,Al)N yields a continuous oxidized layer which is known to offer better protection for subsequent oxidation. Therefore, this oxidized layer on (Ti,Al)N offers better oxidation resistance. During oxidation, Al in the (Ti,Al)N film diffuses to the surface and forms Al2O3. Al2O3 is a highly insulating oxide with low ion mobility and limits oxide growth by acting as a diffusion barrier against oxygen. Therefore the formation of Al2O3 plays a key role in the anti-oxidation properties of (Ti,Al)N films. According to the SEM and EDS results, the oxide layer is composed of two sublayers, an outer layer rich in Al and poor in Ti and an inner layer rich in Ti and poor in Al. |
|
AP-10 Evaluation of Plasma-Sprayed Coating on Creep of the Titanium Alloy
D.A.P. Reis (Instituto Tecnológico de Aeronáutica, Brazil); D.S. Almeida (Instituto de Aeronautica e Espaco, Brazil); C. Moura Neto (Instituto Tecnológico de Aeronáutica, Brazil); M.J.R. Barboza (Escola de Engenharia de Lorena, Brazil); F. Piorino Neto (Comando-Geral de Tecnologia Aeroespacial, Brazil); C.R.M. Silva (Universidade Federal de Brasilia, Brazil) Ti-6Al-4V is currently used in aeronautic and aerospace industry mainly for applications that require resistance at high temperature such as, blades for aircraft turbines and steam turbine blades. The titanium affinity by oxygen is one of main factors that limit the application of their alloys as structural materials at high temperatures. Notables advances have been obeserved in the development of titanium alloys with the objective of improving the specific high temperature strength and creep-resistance properties. However, the surface oxidation limits the use of these alloys in temperatures up to 600°C. The objective of this work was to evaluate the creep behavior of the Ti-6Al-4V alloy focusing on the determination of the experimental parameters related to the primary and secondary creep stages. Yttria (8 wt.%) stabilized zirconia (YSZ) with a CoNiCrAlY bond coat was atmospherically plasma sprayed on Ti-6Al-4V substrates. Constant load creep tests were conducted with Ti-6Al-4V alloy in air for coated and uncoated samples at 600°C to evaluate the oxidation protection on creep of the Ti-6Al-4V alloy. Results indicated the creep resistance of the coated alloy was greater than uncoated in air and more efficient in oxidation protection. Constant load creep tests were conducted on a standard creep machine at stress levels of 125 to 319MPa at 600°C. Results indicated that the creep rates in coated alloy were lower than those of the uncoated in air. |
|
AP-11 The Effect of Multilayer Period on Thermal Stability of CrSiN/AlN Multilayer Coatings
S.M. Kim, B.Y. Lee, S.Y. Lee (Korea Aerospace University, Korea) It is well expected that the thermal stability of the CrN/AlN multilayer coatings could be improved extensively by the addition of the Si elements into the CrN film in the CrN/AlN multilayer coatings as the amorphous microstructure could be induced. In this work CrSiN/AlN multilayer coatings with various bilayer thickness (?) were synthesized using a closed-field unbalanced magnetron sputtering and their crystalline structure, chemical compositions, microstructure and mechanical properties have been investigated with Auger electron spectroscopy (AES), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and Nano-indentation test. Also the thermal stability of the CrSiN/AlN multilayer coatings was evaluated and compared with that of the CrN/AlN coatings by annealing the thin films at temperatures between 600? and 1000? for 30min under vacuum or in air. Preliminary results showed that both the CrSiN/AlN coatings and the CrN/AlN coatings followed a Hall-Petch type relationship between the hardness and the bilayer period, showing an increased hardness with a decrease in bilayer period. However the hardness of the CrSiN/AlN coating was much superior to that of the CrN/AlN coating after annealing at various temperatures due to Si effect on the microstructure. Detailed experimental results will be presented. |
|
AP-12 Cutting Performance of TiSi CN Coated WC Insert Tips
K.-Y. Lee (Pukyong National University, Korea); R. Wei (Southwest Research Institute) We have applied TiSiCN coatings on tungsten carbide cutting inserts tips using PIID (plasma immersion ion deposition) and dual magnetron sputtering deposition technique. In the previous research, we have found that DLC coated WC-Co insert specimens have shown excellent capabilities in the survivability and the low cutting force of the DLC coatings during the dry machining process on Al alloy and the tests were done under a wide range of conditions for the basic tribological properties of DLC coated WC-Co. Results showed that the wear life of DLC-coated cutting inserts was improved almost double and the cutting resistances were drastically reduced. The DLC-coated tools have great advantages for dry machining of Al alloy materials compared to the uncoated mirror finished WC tools which were produced only for Al alloy machining in the markets. However during the cutting performance experiments, carried out in a high speed NC machining center to the dry milling of aluminum alloy we found that the cutting force was low enough to be used commercially but the weak strength and the life of coating were needed to be improved more. The most significant weak point was the strength of DLC coating. For these reason we have developed coating techniques for TiSiCN thin film of more than 5um thickness with various coating conditions in terms of process and doping. Before and after the application tests these specimens were carefully analyzed using SEM with EDS to characterize adhesion of the cutting alloy to form buildup edge on the WC surface and the worn or damaged surfaces. The cross sections of the TiSiCN films were also examined to understand the microstructures effects on the performance. Morphological changes of the DLC coated surfaces were examined using AFM. In addition, Nano-indentation, Scratch test, AES, XPS, Raman, GDOES and GXRD were adopted to study the properties of the TiSiCN thin film and the elemental changes of coatings during the depositions and cutting process. These properties of the coatings were compared with commercially available uncoated and coated WC tools. |