ICMCTF2011 Session AP: Symposium A Poster Session

Thursday, May 5, 2011 5:00 PM in Room Town & Country
Thursday Afternoon

Time Period ThP Sessions | Topic A Sessions | Time Periods | Topics | ICMCTF2011 Schedule

AP-1 Preparation and Annealing Study of CrTaN Coatings on WC-Co
Yung-I Chen, Yu-Ting Lin (National Taiwan Ocean University, Taiwan)

To prevent Co diffusion from cemented carbides at high working temperatures, we fabricated CrTaN coatings by reactive direct current magnetron co-sputtering onto 6 wt.% cobalt cemented carbide substrates, to form diffusion barrier layers. The nitrogen flow ratio, N2/(Ar+N2), during the sputtering process set at 0.4. The deposition rates of CrTaN coatings, 19 to 25 nm/min, depended on the sputter yield of targets. The CrTaN coatings crystallized into a columnar structure, without heating the substrates during the sputtering process. The CrTaN coatings were annealed at 500, 600, and 700oC for 4 hours in air. We evaluated the performance of the diffusion barrier using both Auger electron spectroscopy depth-profiles and X-ray diffraction techniques. We also investigated oxidation resistance of the CrTaN coatings annealed in air, and under a 50 ppm O2-N2 atmosphere, to evaluate the fabricated layers effectiveness as a protective coating for glass molding dies.

AP-2 Microstructural Evolution in NiAl-Cr-Zr Coated Superalloys During High Temperature Annealing and Oxidation
Joel Alfano, Mark Weaver (The University of Alabama)
Nickel-based superalloy components in the hot sections of commercial gas turbine engines are often protected by aluminide coatings due to their ability to function in oxidative and corrosive environments. However, the microstructures of these coated systems are metastable and change in service due to interactions with the environment and interdiffusion with the underlying substrate. The extent of these changes depends critically upon coating microstructure, chemistry, and the environment that the coated component operates in. This paper highlights the influences of chemical composition and post-deposition annealing on the microstructures and properties of NiAl-Zr and NiAl-Cr-Zr overlay bond coatings. In particular, the results indicated that in slightly Ni-rich NiAl-based coatings, coating/substrate interdiffusion and Al-depletion within the coating could be inhibited by increasing the Zr content from 0.3 at.% to 1.0 at.%Zr. However, subsequent additions of 5 at.% Cr to coatings containing 1 at.%Zr, resulted in interdiffusion and Al-depletion levels more similar to low Zr or Zr-free coatings. This paper details the microstructural changes that occur in coated Ni-based superalloys during annealing and/or oxidation at 1050°C as functions of coating chemistry and environment. Results are discussed relative to conventional coating systems.
AP-3 Microstructural Evolution and Thermal Stability of Vertical-Cracked Thermal Barrier Coatings Through Cyclic Thermal Fatigue
Sang-Won Myoung, Kwang-Su Song, Tae-Woong Kang, Zhe Lu, Yeon-Gil Jung (Changwon National University, Korea); Ungyu Paik (Hanyang University, Korea)

Thermal properties and failure mechanisms of thermal barrier coatings (TBCs) are closely related to their microstructure, which is usually determined by the feedstock powder as well as the spraying condition. Recently, TriplexProTM-200 system has been launched to offer an advanced TBC performance resulting from higher particle velocity, lower particle oxidation, and higher coating density, compared with the commercial air plasma spray (APS) system using 9MB gun. Therefore, in this study, TBC samples were prepared by TriplexProTM-200 system using different commercialized powders and the microstructure of TBC was controlled by the reheating the surface of TBC without powder feeding in same equipment. The relatively porous TBC was prepared with METCO 204 C-NS and the relatively dense TBC with METCO 204 NS. The microstructure of the top coat in TBCs was just controlled, and the bond coat with about 300 mm thickness in the both top coats was prepared with AMDRY 962. The cyclic thermal exposure tests were performed at the surface temperature of 1100℃ with the temperature difference of 150℃ between the surface and bottom of sample, with a dwell time of 1 h till 24000 EOH (1143 cycles) or delamination, in a specially designed apparatus. The distance parameter is more effective in creating the vertical cracks than the gun speed, with less and shorter vertical cracks in the relative porous TBC. The hardness values on the sectional plane are gradually changed in the both vertical-cracked TBCs, indicating that those of the relatively porous TBC are changed from 6.5 (interface of the top and bond coats) to 4.2 GPa (surface of the top coat) and those of the relatively dense TBC being changed from 7.8 to 4.5 GP. After the thermal exposure tests, the vertical cracks reach down to the interface of the top coat and the TGO layer in the relatively dense TBC, and the hardness and toughness values are decreased and increased, respectively, in the both TBCs. The both vertical-cracked TBCs show a sound condition without any evidence of delamination, while the relatively dense TBC without the vertical cracks is delaminated within 8000 EOH (381 cycles) or shows an evidence of delamination at the interface of the top coat and the TGO layer after 8000 EOH. Consequently, in the both cases, the TBCs with the vertical cracks are more efficient in thermal durability than those without the vertical cracks, especially in the relatively dense TBC. The relationship between the microstructural evolution and thermomechanical characteristics of the TBCs with and without the vertical cracks is discussed.

AP-4 Effect of Pre-Nickel Plating on the Microstructure and Phase Constitution of Hot-Dipped Aluminide Coating on Mild Steel
Wei-Jen Cheng, Chaur-Jeng Wang (National Taiwan University of Science and Technology, Taiwan)
Pre-nickel plated Mild steel was coated by hot-dipping into a molten bath containing pure Al at 670°C . The effect of pre-nickel plating layer on the microstructure and phase constitution of the aluminide layer was investigated by using a combination of scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD). The results showed that the pre-nickel plating layer of 20 μm was dissolved and reduced to 12 μm after hot-dipping for 5 seconds. Also, a continuous layer, composed of Ni2Al3 + NiAl3 + (Fe,Ni)2Al9, formed above the nickel plating layer, while a small amount of NiAl3 phase scatted in the aluminium topcoat. In the aluminide layer after hot-dipping for 60 seconds, a portion of nickel plating layer has consumed, leading to the Ni-Al phases began to transform into FeAl3 and (Fe,Ni)2Al9. As the dipping time increased, the aluminide layer was composed of minor FeAl3 and major Fe2Al5. In comparison with the hot-dipped aluminide mild steel without pre-nickel plating, the phase constitution and the thickness of the intermetallic layer with pre-nickel plating after long-term dipping time are the same as in the intermetallic layer without pre-nickel plating.
AP-5 Non Destructive Assessment by Photo-Stimulated Luminescence of EB-PVD Thermal Barrier Coatings Damaged by Laser Shock Spallation
Gregory Fabre, Vincent Guipont, Michel Jeandin (Centre des Materiaux - Mines ParisTech, France); Françoise Passilly, Thierry Maffren (ONERA, France); Annie Pasquet, Jean-Yves Guedou (SNECMA Safran Group, France)

During the two last decades, plasma Spray and EBPVD TBCs have been intensively used in turbines for aircraft propulsion and power generation. However, interfacial damages due to thermal exposure and oxidation remain not totally understood. Thus, the knowledge on lifetime prediction of TBCs before spallation is still limited. In this work, the laser shock spallation has been applied to generate interfacial defects as those occurring in TBCs during thermal cycling. This method is derived from the LASAT (Laser Shock Adhesion Test) protocole to determine adhesion of ceramic coating. Depending on the laser energy and dimensions of the LASATested coatings (layers thicknesses, laser diameter mainly), it has been evidenced that the circular crack size located at the zirconia-bond coat interface can be easily varied for further non destructive assessments by photo-stimulated luminescence. Thus, different damage areas at bond coat-zirconia interface have been realized without the removal of TBC ceramic top-coat for coated samples with different aging periods of one-hour cycles at 1100°C (0 and 100 cycles). The photo-stimulated luminescence was used as a powerful Non-Destructive Assessment of the damages induced by laser shock through the measure of the released stress in the TGO and the corresponding variation in the photo-excitation of Cr3+ ions within the thermally grown oxide (TGO). The damaged areas were detected by this method and the dimensions were also measured accurately using scanned images obtained by photoluminescence piezospectroscopy. The crack damages were also investigated by visual inspection and SEM cross-sectioned observations for further comparison with actual dimensions of the interfacial defects that were deliberately induced by LASAT.

AP-6 Pore Density Control of Al Thin Films with Process Conditions of Magnetron Sputtering
Ji-Hoon Yang, Jae-In Jeong, Seung-Hyun Jang, Hye-Sun Park (Research Institute of Industrial Science and Technology, Korea)
Al thin films deposited with magnetron sputtering generally have a columnar structure. The columnar structure of Al films has many pores, which is origin of degradation of substrates. For the prevention of the degradation, the pore density of Al films should be decreased. In this study, the method for decrease of the pore density is suggested. Al thin films are deposited with a magnetron sputtering on cold rolled steel sheets, which the sputtering source is unbalanced magnetron source. The important factor for the decrease of the pore density is the direction and intensity of an external magnetic field by an electromagnet. Forward magnetic field is applied the sputtering source, so that the pore density of Al films increase. On the other hand, reverse magnetic field is applied which decrease the pore density of the film. In the optimum condition, the Al film shows the density of 94.7 % compared with that of bulk Al.
AP-7 Thermal Stability and Corrosion Resistance of AlTiON/CrON Multilayered Coating
Wei-Yu Ho, Li-Way Shen, Zhong-Shen Yang, Chi-Lung CHang, Da-Yung Wang (Mingdao University, Taiwan)
TiAlN/CrN coatings possess superior hardness, good thermal and chemical stability due to both multi-component constituents and a multilayer structure in nanoscale thickness. To further improve thermal stability and corrosion resistance of (Ti,Al)N/CrN multilayered coatings for aluminium die casting applications, the addition of oxygen into the (Ti,Al)N/CrN multilayered coatings by cathodic arc deposition was investigated. The studied coatings were obtained with dual Al0.75Ti0.25 and Cr targets at the O2 and N2 mixtured gas flows in this study. The structure of the coating was explored with B1 NaCl type structure in which AlTiN and CrN formed multilayer in the coating. The formation of oxide phases by introducing oxygen to react with Al, Cr and Ti was confirmed by X-ray photoelectron spectroscopy. The higher thermal stability of oxygen-added AlTiN/CrN coating was obtained compared to that of AlTiN/CrN coating. The imersion tests were evaluated in aluminium melt. Compared to AlTiN/CrN, the addition of oxygen into AlTiN/CrN multilayered coatings improved the corrosion resistance. The performance of corrosion resistance is dramatically enhanced as a result of oxygen content in the AlTiN/CrN multilayered coatings.
AP-9 Nano Modified NiCrAlY Coatings for High Temperature Applications
Smita Sahu, A.S. Khanna (Indian Institute of Technology, India)
Oxidation behaviour of NiCrAlY powder, blended with nano and micro sized Al2O3 and Y2O3 was studied to understand the effect of nano oxide powder dispersion. The blended powders were applied on the IN 718 by HVOF technique. The present work compares the oxidation behavior of NiCrAlY dispersed with nano and micro Y2O3, Al2O3 oxide. Coated samples were characterised by XRD, SEM/EDAX in terms of surface composition, scale cross section and the identification of different phases.The oxidation tests were carried out at 1223K, 1323K, 1423K in air. Oxidation kinetcs were determined from these tests which infer that nano and micro size Al2O3 and Y2O3 was effective in lowering oxide growth.
AP-11 Thermal Properties Characterization of Gradient RE2Zr2O7/YSZ Bilayer Thermal Barrier Coatings Obtained by the APS Method
Grzegorz Moskal, Aleksandra Rozmyslowska-Grund (Silesian University of Technology, Poland)

Presented investigations will concern characteristics of the gradient TBC double-layer type Gd2Zr2O7 - ZrO2Y2O3 (YSZ). The layers were placed on a nickel superalloys type AMS5599 with an bond-coat type NiCrAlY, obtained by the VPS (vacuum plasma spraying) method. Ceramic layers were applied in a result of plasma spraying by the APS method with powders of a general formula Gd2Zr2O7 and ZrO2Y2O3 obtained by a spray drying method. Four types of samples were prepared. They varied according to volumetric fraction of ceramic powders situated in loaders during APS process (Gd2Zr2O7 and ZrO2Y2O3 powders volumetric fractions, respectively: 25% - 75%; 50% - 50%; 75% - 25%; 100% -100%).

The last sample with 100% - 100% volumetric fraction - bilayer coating was obteined in different way than others: ZrO2Y2O3 layer was applied firstly and than Gd2Zr2O7 layer was sprayed on it.

A range of investigations, presented in the paper will comprise:

· evaluation of microstructure of a ceramic layer from a point of view of thickness, quality of a layer and quantity characteristics of cracks and pores architecture;

· evaluation of thermal diffusivity of a ceramic layer within a range of temperature 25-1100°C;

· determination of thermal conductivity of the TBC louble-layer type Gd2Zr2O7 - ZrO2Y2O3.

Results, presented in the paper, are effects of long-running investigations, carried out by the Department of Materials Science in the Silesian University of Technology, and these investigations concerned heat- resisting coatings and layers type TBC.

Financial support of Structural Funds in the Operational Programme –Innovative Economy (IE OP) financed from the European Regional Development Fund -Project No POIG.01.01.02-00-015/09 is gratefully acknowledged.
AP-12 Characteristics of Microstructural Phenomena in TGO Zone of TBC Layer of Re2Zr2O7 Type
Grzegorz Moskal, Radosław Swadźba (Silesian University of Technology, Poland)

The scope of this study covers characterization of the microstructure and chemical composition of the TGO zone in the TBC layers isothermally annealed at 1100°C in air or argon. Conventional layers based on 8YSZ powders and a new type of layer based on a zirconate powder Gd2Zr2O7 with a pyrochlore structure were studied. Annealing proceeded over 2 or 10 h in argon, and over 10 h in air. The samples were microstructurally analyzed using scanning microscopy and an assessment of the chemical composition of the micro-areas was conducted. The thickness and structure of the oxide zone was determined for the different annealing atmospheres and annealing times. TBC coatings were obtained by the APS method, in which the standard parameters for the spraying process were applied. Analysis showed that the TGO zone thickness of the new type of layer was approx. 50% smaller in comparison with the thickness of the conventional TBC (YSZ). In both cases, the main ingredient of this zone was aluminum oxide. The thickness of the argon-annealed oxide layer was larger than the thickness of the air-annealed layer, and complex oxides formed with nickel and chromium on the outer parts of the TGO in the second case.

Financial support of Structural Funds in the Operational Programme –Innovative Economy (IE OP) financed from the European Regional Development Fund -Project No POIG.01.01.02-00-015/09 is gratefully acknowledged.
AP-13 Comparison of Surface Quality, Machining Time in P-20 Steel and Alumold in the Manufacture of Thermoplastic Injection Mold
Wilmar Mattes (SENAI-SC, Brazil)
Analysis of surface quality, strength and time in machining using alumold and steel P – 20 (WNr 1.2312) in the manufacture of thermoplastic injection mold where the two materials were compared and the same techniques using the HSM. Alumold Forged is a high quality, high strength aluminum alloy intended for the plastic forming industry and for other tooling applications. With its high strength and surface hardness it is suitable for polishing and texturing and is wieldable. It is supplied in the forged, heat treated, quenched, cold compressed and aged condition. Alumold Forged possesses better than normal mechanical properties in all sizes, excellent thermal conductivity and very good machinability together with good stability. Within a project a test stand for the direct measurement of dynamic cutting force coefficients was designed and implemented. Test results the need for more complex dynamic cutting force coefficients was designed and implemented. Test results show the need for a more complex dynamic cutting force model in order to reach an acceptable level of accuracy in stability simulation for HSC machining operations.
AP-14 Phase Transformation of MoS2-Nb Composite Coated Films at the High Temperatures
Ihsan Efeoglu (Atatürk University, Turkey); Sabri Altintas (Bogazici University, Turkey); Ersin Arslan (Atatürk University, Turkey); Ozlem Baran (Erzincan University, Turkey); Deniz Ugur (Bogazici University, Turkey)
The crystalline transformation of MoS2-Nb composite films prepared by magnetron sputtering as a function of high temperature vacuum environment has been studied using X-ray diffraction. Crystallization heat treatments were carried out in situ heat treatment. Variations in the transformation as function of the temperature for each sample were attributed to differences in the elemental concentration in the composite structured films.
AP-15 Cyclic Oxidation Behavior of HVOF Bond Coatings Deposited on La- and Y-doped Superalloys
Michael Bestor, J. Allen Haynes, Bruce Pint (Oak Ridge National Laboratory)

One suggested strategy for improving the performance of thermal barrier coating (TBC) systems used to protect hot section components in gas turbines is the addition of low levels of dopants to the Ni-base superalloy substrate. For the more aggressive environment expected for coal-derived, synthesis gas-fired turbines, this strategy may be effective in retaining TBC durability. To quantify the benefit of these dopants, coupons of three commercial alloys with different Y and La contents were coated with a NiCoCrAlYHfSi bond coating by high velocity oxygen flame spraying. Coupons were oxidized in cyclic exposures at 1050°, 1100° and 1150°C; and the oxidation rate and alumina scale adhesion were compared in an effort to better understand the benefit of superalloy dopants. In addition, some of these substrates will be spray coated with yttria-stabilized zirconia to determine the effect of dopants on coating lifetime.

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This research was sponsored by the U.S. Department of Energy, Office of Coal and Power R&D, Office of Fossil Energy, (R. Dennis program manager).

Time Period ThP Sessions | Topic A Sessions | Time Periods | Topics | ICMCTF2011 Schedule