ICMCTF2007 Session AP: Symposium A Poster Session

Thursday, April 26, 2007 5:00 PM in Room Town & Country
Thursday Afternoon

Time Period ThP Sessions | Topic A Sessions | Time Periods | Topics | ICMCTF2007 Schedule

AP-1 A High-Temperature Oxidation Resistance of Novel Si-B-C-N Coatings Prepared by Reactive Magnetron Sputtering
S. Hreben, J. Vlcek, S. Potocky, J. Kalas, P. Zeman, K. Rusnak (University of West Bohemia, Czech Republic); V. Perina (Academy of Sciences of the Czech Republic); Y. Setsuhara (Osaka University, Japan)
Based on our preliminary results comparing the oxidation resistance of Si-C-N and Si-B-C-N coatings, a detailed systematic investigation of high-temperature oxidation resistance of the Si-B-C-N coatings in dependence on process parameters has been carried out. All the coatings prepared for the oxidation tests were deposited on Si(100) substrates by reactive dc magnetron co-sputtering using a single C-Si-B or B4C-Si target in nitrogen-argon gas mixtures. Effect of the magnetron target composition, gas mixture composition, rf substrate bias voltage and the substrate temperature on high temperature oxidation resistance of the coatings was investigated using a symmetrical high-resolution Setaram TAG 2400 thermogravimetric system in a synthetic air up to a 1300 °C substrate limit. The elemental composition of the coatings was determined by Rutherford backscattering spectrometry (Si, B, C, N, O, Ar) and elastic recoil detection (H) methods. Most of the prepared Si-B-C-N coatings, typically 2-4 µm thick, with a purely amorphous nanostructure, exhibited very high oxidation resistance up to the 1300 °C substrate limit with a maximum mass change Δm≤8 µg/cm2 only. A systematically higher oxidation resistance (almost zero mass changes) was achieved for the Si-B-C-N coatings prepared using the B4C-Si targets, compared to the corresponding C-Si-B targets, under the same experimental conditions. An increased content of oxygen detected in a top surface layer (less than 150 nm) at its low (less than 1 at.%) content in volume of the coatings is a consequence of formation of a very thin dense surface barrier layer (mainly composed of Si and O) during the annealing in air, which prevents inward oxygen diffusion into the Si-B-C-N material. Formation of the mentioned surface barrier layer and conservation of the purely amorphous nanostructure of Si-B-C-N coatings were confirmed by HRTEM cross sectional images taken after treatment.
AP-2 Temperature Effects on the Cyclic Oxidation Behavior of Aluminide Coatings on Various Superalloys
J.A. Haynes, B.A. Pint (Oak Ridge National Laboratory); Y. Zhang (Tennessee Technological University); K Cooley, I.G. Wright (Oak Ridge National Laboratory)
The influence of exposure temperature on the oxidation behavior of simple and platinum aluminide coatings on various superalloy substrates was investigated. Coatings of β-NiAl, β-NiPtAl and γ-γ NiPtAl were fabricated on various compositions of alloy 142 and N5 substrates. Selected coatings were exposed to cyclic oxidation testing in dry oxygen at 1050, 1100, and 1150°C. There was a clear influence of substrate composition on the oxidation behavior of β-NiAl coatings at all three temperatures. The β-NiAl coatings on alloy N5 exhibited superior oxidation performance to those on alloy 142 at all three temperatures. Substrate S degraded the oxidation behavior of β-NiAl on various alloy N5 substrates at all three temperatures. The impact of substrate composition, especially S content, was measurably reduced for β-NiPtAl coatings at all three temperatures, as compared to β-NiAl. Simple γ-γ NiPtAl coatings showed promising oxidation performance at 1100 and 1150°C on alloy N5, but were more sensitive to substrate composition than β-NiPtAl coatings on the same substrates.
AP-3 Erosion Wear and Corrosion Behaviors of M2 Steel Arc-Deposited Cr-N-O Double-Layered Coatings
C.-H. Hsu, C.-J. Huang, Y.-D. Chen (Tatung University, Taiwan)
In this study, M2 high-speed steel was used as the substrate to deposit various Cr-N-O double-layered coatings by cathodic arc deposition process under the same nitrogen flow and the different oxygen flows, respectively. Surface morphology of the coated specimens was observed after single particle erosion test and wear resistance was explored by using ball-on-disk wear test. Polarization tests were also performed to evaluate the corrosion resistance in 3.5wt% NaCl solution. In addition, microstructure and chemical composition of the coatings were analyzed by X-ray diffraction (XRD) and electron probe microanalysis (EPMA). The results showed that CrN/Cr2O3 coatings had a highest value in hardness and a lowest friction coefficient as well as better corrosion resistance among the coated and uncoated M2 steels.
AP-5 The Influence of Aluminum Addition on the Thermal Stability and Microstructure in the Ternary NiPAl Coatings
C.-Y. Kang, J.G. Duh, C.-H. Lin (National Tsing-Hua University, Taiwan)
The ternary NiPAl alloy coating was fabricated by RF magnetron sputtering technique with dual targets of NiP/Cu and pure Al. Electroplating NiP process was introduced to obtain the NiP compound target with various phosphorous contents from 12~18 at.% after modification of the processing parameters. The composition of the coating was analyzed by electron probe microanalysis (EPMA). To evaluate the influence of the doping Al in NiP deposit, differential scanning calorimeter (DSC) analysis was employed to characterize the temperature of phase transformation. After heat treatment at various temperatures from 350 to 550°C for 4h, the structure at different annealing temperature was studied by X-ray diffraction and transmission electron microscope (TEM). The hardness of the coating could be acquired by the nanoindentation. It was demonstrated that the NiPAl coating exhibited a relatively higher hardness and also better thermal stability than the pure NiP coatings after annealing at elevated temperature. Key words: electroplating; NiPAl coating; TEM; XRD; nanoindentation; crystallization behavior.
AP-6 Effect of Nitrogen Flow on the Characterizations of Quaternary CrAlSiN Coatings at Elevated Temperature
S.-K. Tien (National Tsing-Hua Univerisity, Taiwan); Y.Z. Tsai, J.G. Duh (National Tsing-Hua University, Taiwan)
CrAlSiN coatings are reactively fabricated on the Si substrate from metallurgical Cr0.45Al0.45Si0.10 alloy target by r.f. magnetron sputtering. The thermal stability of CrAlSiN coatings, including oxidation resistance and hot hardness, are investigated after annealing at temperatures between 800 and 1100°C for 1 hr in air. The phase identification, chemical states, oxide content on the surface, and hardness of CrAlSiN coatings prior to and after heat treatment are analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron probe microanalysis (EPMA), and Nanoindentation, respectively. The oxidation resistance of CrAlSiN coatings with nitrogen flow above 10 SCCM is excellent after heat treatment at 900 and 1000°C. Especially for coatings with 10~15 SCCM nitrogen flow, the oxygen contents on the surface of CrAlSiN coatings are as long as only 2.7 at.% and 6.5 at.%, respectively. Furthermore, the hardness of CrAlSiN coatings increases and reaches a maximum value of 30.4±1.4 GPa with nitrogen flow ranged from 0 to 30 SCCM. After heat treatment at 900°C, hot hardness of CrAlSiN coatings with nitrogen flow of 15 SCCM still maintains as high as 26 GPa. The effect of Si addition on hardness and oxidation resistance in the CrAlSiN coatings are also evaluated by XPS and transmission electron microscopy (TEM).
AP-8 Microstructures and Oxidation Behavior of Aluminized, Pt-Aluminized HVOF Sprayed CoNiCrAlY Coatings
P.-C. Tsai (National Formosa University, Taiwan); J.-W. Lee (Tung Nan Institute of Technology, Taiwan); C.-L. Chang (Mingdao University, Taiwan)

In this investigation, The Hastelloy-X superalloy coupons were overlaid a CoNiCrAlY bond coating by high velocity oxygen fuel (HVOF) spraying process. For Pt aluminizing samples, a platinum thin film around 7.5 µm thick was further coated on the surface of CoNiCrAlY coating by magnetron sputtering deposition. Then, the aluminizing and Pt aluminizing samples were pack aluminized at 850°C for 4 hours to produce (Ni,Co)Al and PtAl2 phases on the surface, respectively. After that, all the specimens were subjected to a furnace thermal cycling test at 1100°C. The effects of aluminizing, Pt-aluminizing on the oxidation resistance and failure mechanism of the coatings were evaluated.

The results of this study showed that roughness of the CoNiCrAlY coating did not change after aluminizing or Pt-aluminizing. The Pt-aluminizing process improved the oxidation resistance of HVOF sprayed coating significantly while the aluminizing process had inferior effects. The oxide scale spalled after 50 and 100 hours oxidation for sprayed sample and aluminized sample respectively, while the oxide scale attached well to the substrate for the Pt-aluminized sample after 150 hours test.

The microstructures analysis of the as-processed and tested coatings were carried out by using optical microscope (OM), electron microscope (SEM), X-ray diffractometer (XRD), and electron probe microanalyser (EPMA) in an effort to relate the coating structure to the performance and the degradation mechanisms.
AP-9 Measuring and Modeling the TBC Damage Kinetics by using Acoustic Emission Analysis
D. Renusch (Karl-Winnacker-Institut der DECHEMA e.V., Germany); M. Schuetze (Karl-Winnacker-Institut der DECHEMA e.V, Germany)
The life of the thermal barrier coating (TBC) prior to failure is dominated by micro-cracking in both the thermally grown oxide and the yttria stabilized zirconia top coat. The damage generated by this micro-cracking is expected to be a primary life limiting factor. Current techniques for characterization of the accumulated damage are limited. Consequently, there is interest in using acoustic emission analysis to help develop understanding of this degradation process. The damage accumulation of APS-TBC has been measured by acoustic emission analysis during cyclic oxidation at 1150, 1100 and 1050°C. One effect of accumulated damage is that it lowers the strain tolerance (i.e. critical strain) of the TBC. Acoustic emission analysis is also being used in a four-point bend test for the purpose of determining the critical strain of the TBC. In this test the critical strains for the onset of delamination and the onset of through cracking are found. This test has been applied to both as-sprayed and pre-oxidized samples. The results of these acoustic emission measurements have been embedded into a phenomenological lifetime prediction mode, which illustrates both the time and temperature dependents of the TBC damage kinetics.
AP-10 Evaluation of Aluminium-Coating on Ferritic Steels by CVD-FBR Technology in Steam Oxidation
F.J. Bolívar, L. Sánchez, M.P. Hierro, J.A. Trilleros, F.J. Pérez (Universidad Complutense de Madrid, Spain)
In recent years an extensive materials development has taken place with regard to new steels for fossil power stations. This development work was mainly focussed on the mechanical high temperature strength up to 650°C and increase the oxidation resistance of the ferritic steels with chromium contents between 9 and 12%. These steels are usually used in boiler or supercritical steam turbines, which operate at temperatures between 500-600°C. In the last years numerous investigation in develop of coatings has been realized with the aim the protected them against the oxidation in order to allow operation of steam turbines at 650°C. In this study, Al protective coatings were deposited by CVD-FBR on two ferritic steels (P-91 and HCM-12A) followed by a diffusion heat treatment, have shown to be protective at 650°C under steam for at least 3000 hours of laboratory steam exposure under atmospheric pressure. Morphology and composition of coatings were characterized by different techniques, such as scanning electron microscopy (SEM), electron probe microanalysis, and X-ray diffraction (XRD). The results show a substantial increase of steam oxidation protection afforded by Al-coating by CVD-FBR process.
AP-11 Corrosion Behaviors of Cr(N,O)/CrN Multi-layered Coatings by Filtered Cathodic Arc Deposition
W.-Y. Ho, C.-L. Chang, C.-H. Shen (MingDao University, Taiwan)
The purpose of this study is to improve the corrosion resistance of Cr-based PVD coatings for tool applications. Cathodic arc deposition is a well known technique to deposit hard coatings on tools for industrial applications. However, dense hard coatings are always accompanied with macroparticles which cause defects of the coatings. In this study, the Cr(N,O)/CrN coatings were deposited on tool steels with different layer structures including double-layer and multi-layer using filtered cathodic arc deposition process. The as-deposited specimens were carried out with treatment to remove the macroparticles before test. By introducing the mixture of O2/N2 gas flow, the Cr(N,O) layer contained Cr, N, O elements was obtained during the coating process. CrN layer was first deposited on tool steel as an interlayer to ensure better adhesion. Then, Cr(N,O) was deposited as a surface layer formed as double layers. The multi-layered Cr(N,O)/CrN was conducted by changing the deposition process in the sequence of CrN-Cr(N,O)-CrN-Cr(N,O). The phase structure, chemical composition, and morphology of coatings were observed by utilizing X-ray diffractometer, Auger electron spectrometer and AFM. The corrosion behavior of coatings was investigated using polarization curve tests. Results show that Cr(N,O)/CrN multi-layered coatings exhibit the best corrosion resistance with filtered arc sources .
AP-12 Accuracy of Localized High Temperature Measurements In TBCs Using Luminescence Doping
B. Heeg (MetroLaser, Inc.); M. Chambers (University of California, Santa Barbara); T.P. Jenkins (MetroLaser, Inc.); D.R. Clarke (University of California, Santa Barbara)
Recent advances in the ability to measure the temperature inside thermal barrier coatings using localized luminescence doping into the crystal structure of the TBC itself has raised the question of how accurately such measurements can be made. An analysis is presented, based on experimental measurements and modeled luminescence decays of Eu3+:YSZ, that includes detector sensitivity, various noise contributions, laser pulse energy, background interference and luminescence decay dynamics. The analysis reveals the conditions under which an error of less than 1% may be achieved at temperatures of 1000 °C, providing a promising alternative to infrared pyrometry for in-situ turbine engine temperature monitoring.
AP-14 A New Approach to Improve SCC Resistance of Austenitic Stainless Steel with a Thin CrxN1-x Film, Deposited by Arc Physical Vapor Deposition
W. Tillmann, E. Vogli, S. Mohapatra (University of Dortmund, Germany)
Excellent mechanical properties coupled with good corrosion resistance, rendered austenitic stainless steel (ASS) as a widely used material for all types of engineering applications. However, the susceptibility to stress corrosion, in the simultaneous presence of stress and corrosive media, limits the application in special cases. In this research, a new approach has been adopted i.e. coating the steel surface with a thin passive layer of chromium nitride (CrxN1-x, 0
AP-15 Erosion Performance of Abradable Coating Materials
J.R. Nicholls, T. Rose (Cranfield University, United Kingdom); C. Sellars, D.S. Rickerby (Rolls-Royce plc., United Kingdom)

Abradable coatings are critical to the efficient and effective sealing, at blade tips, in both the compressor section and turbine of advanced gas turbine engines. Ineffective sealing results in lost performance and can lead to increased CO2 emissions and lower specific fuel consumption, due to increased fuel burn.

This current research focuses on the erosion performance of abradable coating materials used for the compressor section in advanced gas turbines. The aim is to develop robust abradable materials capable of resisting the ‘rub’ necessary to ensure good clearance control, whilst providing enhanced glancing angle erosion performance against entrained particles in the gas stream.

Abradable materials, based on Al-Si plus dislocator phase design or nickel plus dislocation phase design, have been manufactured to provide samples for erosion testing with a range of densities, hardness and elastic properties. Each class of material has been erosion tested using Cranfield’s high velocity gas gun erosion rig for angles of impingement between 15-90°.

The mechanisms of damage accumulation and hence material removal, have been studied as a function of abradable manufacture, microstructure, porosity and dislocator phase distribution.

Erosion rates reflect an interplay between the abradable microstructure and the energy density of the impacting particle. The abradable microstructure, impact dynamics and the mechanisms of damage accumulation, leading to material loss, will be discussed in this paper.
AP-16 Influence of a Ce Surface Treatment on the Oxidation Behavior of Type 347 Stainless Steel
D. Alman, P. Jablonski (National Energy Technology Laboratory)
A surface treatment was applied to the surface of Type 347 stainless steel to enhance oxidation resistance. The treatment consisted of dip coating coupons in a CeO2 and halide activator slurry, followed by a thermal treatment at 900C in an inert atmosphere for 12 hours. Cyclical oxidation tests were conducted at 800C in either dry air or air+3%H2O. In dry air, the treatment reduced the oxidation rate (reduced the magnitude of weight gain) of the alloy by a factor of three. Protective chromium based oxide and spinel ((Mn,Cr)3O4 and (Cr,Fe)2O3) phases formed on the surface of the untreated and treated alloy. More significantly, the treatment suppressed the oxide scale spallation that occurred upon cyclical exposure of this alloy to moist air. In moist air, less protective chromite, magnetite and hematite formed as oxide products on the surface of the base alloy. The treated alloy did not spall during exposure to moist air, and interestingly, the treated alloy possessed similar oxidation rates (magnitude of weight gain) in both moist and dry air. The same protective chromium based oxide and spinel phases formed on the surface of the treated alloy exposed to both moist and dry air. In the aggressive moist environment, the Ce surface treatment suppressed the formation of less protective iron-oxides, and concomitant oxide scale spallation during thermal cycling.
AP-19 Degradation of Yttria Stabilized Zirconia Topcoat in Thermal Barrier Coatings by V2O5 and P2O5
P. Mohan, Y.H. Yuan (University of Central Florida); V. Desai (New Mexico State University); Y.H. Sohn (University of Central Florida)
Presence of vanadium and phosphorus impurities in petcoke and coal/petcoke blends used in IGCC plants warrants a clear understanding of high temperature materials degradation for the development of fuel-flexible power generation plants. In this study, degradational reaction mechanisms of free-standing plasma sprayed yttria stabilized zirconia (YSZ) in contact with V2O5 and P2O5 were investigated at temperatures up to 1200°C. Phase transformations and microstructural development were examined by using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Molten V2O5 reacted with solid YSZ to form zirconium pyrovanadate (ZrV2O7) at temperatures below 747°C. However, at temperatures above 747°C, molten V2O5 reacted with YSZ to form yttrium vanadate (YVO4). Formation of YVO4 led to the depletion of Y2O3 stabilizer and the disruptive transformation of the metastable tetragonal zirconia phase to the monoclinic and fluorite-cubic phases (t´ -- f + m). Besides this, studies on degradation of YSZ by P2O5 revealed that the formation of zirconium pyrophosphate (ZrP2O7) was the only reaction mechanism. At temperatures as low as 200°C, molten P2O5 was observed to react with solid YSZ to yield zirconium pyrophosphate, which led to the depletion of ZrO2 in YSZ. It was also observed that the formation of significant amount of ZrP2O7 resulted in the transformation of the metastable tetragonal zirconia phase to the fluorite-cubic phase (t´ -- f) due to the enrichment in yttria content of YSZ.
Time Period ThP Sessions | Topic A Sessions | Time Periods | Topics | ICMCTF2007 Schedule