Symposium A Poster Session

Thursday, May 2, 2013 5:00 PM in Room Grand Hall

AP1 Thermal Stability of Ir – Re Coatings Annealed in Oxygen Containing Atmospheres
Shih-Chang (S.C.) Lin (National Tsing Hua University, Taiwan, Republic of China); Yung-I Chen (National Taiwan Ocean University, Taiwan, Republic of China); Hung-Yin Tsai (National Tsing Hua University, Taiwan, Republic of China); Kuo-Cheng Liu (National Taiwan Ocean University, Taiwan, Republic of China); Yung-Hsing Chen (Young Optics Inc.)
Ir–Re coatings were widely applied as protective coatings on glass molding dies. Because of the glass molding process in mass production was performed in an oxygen containing atmosphere at high temperature, the protective coatings need to endure cyclic annealing treatments. Less attention has been paid to the oxidation and thermal stability of the Ir–Re coatings. In this study, Ir–Re coatings were prepared by co-sputtering. The constant-temperature annealing treatments were conducted at 600 oC under atmospheres of 10 ppm O2–N2, a glass molding atmosphere, and 1 % O2–Ar, an accelerating oxidation atmosphere, respectively. The thermal cyclic test was performed between 200 and 600 oC under a 10 ppm O2–N2 atmosphere. The variations in crystalline structure, nanohardness, surface roughness, residual stress and chemical composition profiles in depth after various annealing times were investigated.
AP2 Steam Oxidation of Al Slurry Coatings Deposited on Super304H, TP347H and TP347HFG
Maud Seraffon, Tony Fry (National Physical Laboratory, UK)

Commercial, regulatory and social pressures have led the energy industry to improve power plant efficiency by increasing the operating temperatures and pressures of combustion plant, moving from conventional plant, with operating steam temperatures and pressures of 540 °C and 180 bar, to advance ultra-supercritical plant with steam temperatures >700 °C and pressures > 300 bar. Such an increase in operating conditions would increase the plant efficiency from 42% to an estimated 55%. These increased operating conditions place current materials in extremely aggressive environmental conditions. Current ferritic-martensitic steels do not possess the high temperature capability, with a temperature limit of ~620 °C. There is a need therefore to move towards using more austenitic alloys. Experience of austenitic materials in the US has shown that some alloys are susceptible to early spallation under steam oxidation conditions leading to rapid breakaway oxidation. One method to prevent this is the use of high temperature protective coatings. Aluminide coatings have been developed for use on ferritic steels with encouraging results. These coatings combine good high temperature oxidation resistance through the growth of an Al2O3 scale and, in the case of Al slurry, the possibility to apply the coating on an industrial scale at moderate cost. However, there is little information and understanding of the behaviour of the same coatings on austenitic alloys. The purpose therefore of the work reported here was to examine and generate the necessary data on the microstructural evolution of Al slurry coated austenitic alloys subjected to oxidising atmosphere of 100% flowing steam at 700 and 750 °C for times up to 5000 hours at atmospheric pressure. The coating prevented breakaway oxidation on samples exposed at 700 °C and delayed the onset of breakaway until 3000 hours at 750 °C showing the protective potential of the coating. Measurement of the Aluminium diffusion showed that it diffused outwardly to form a protective Al23 layer and inwardly into the substrate to form an Aluminium diffusion zone and precipitates of AlN and Ni-Al. Despite differences in Al diffusion behaviour between the three austenitic alloys, indicating an influence of initial composition and grain size, the time at which breakaway oxidation occurred was identical, suggesting that the Al slurry coating provided the same level of protection on the three alloys.

This paper presents the steam oxidation results for the three coated alloys comparing the oxidation behaviour between the three and also referencing back to the performance of the uncoated alloys.

AP5 Structure of Pd-Zr and Pt-Zr Modified Aluminide Coatings Deposited by CVD Method on Nickel Superalloys
Maciej Pytel (Rzeszów University of Technology, Poland); Ryszard Filip, Marek Goral (Rzeszow University of Technology, Poland); Jan Sieniawski (Rzeszów University of Technology, Poland)
In the article the structure of newly developed modified aluminide coating will be characterized. The coatings were obtained by Pt and Pt electroplating and CVD low-activity aluminizing process. The Pt and Pd electroplated samples were modified by Zr doping during CVD-low activity aluminizing as well. Coatings were deposited using BPX Pro 325S semi-industrial CVD system on Research and Development Laboratory for Aerospace Materials at Rzeszow University of Technology. In the paper the process parameters were described and the results of microstructural analysis as well. The microstructure analysis was conducted using Hitachi S-3400 scanning electron microscope equipped by EDS analyzer (Thermo). The XRD and GDOES analysis were also made. The results showed that thickness of coatings was in range 40-70 mm. The obtained coatings were single-phase type (Ni,Pt/Pd)Al. The newly produced coatings will be a new type of bond coat for thermal barrier coatings with ceramic layer deposited by EB-PVD coating.
AP6 TBCs Deposited using New EB-PVD Smart Coater System
Andrzej Nowotnik (Rzeszow University of Technology, Poland); Marek Goral, Jan Sieniawski, Maciej Pytel (Rzeszów University of Technology, Poland)
In the article the characterization of new type of EB-PVD device will be described. Especially the comparison with actually used industrial EB-PVD systems will be conducted. The current status of electron beam physical vapor deposition in ceramic coating development will be analyzed. The Smart Coater device is a new solution developed by ALD Vacuum Technology in cooperation with Research and Development Laboratory for Aerospace Materials in Rzeszow University of Technology. The newly developed system is smaller and cheaper in comparison with other EB-PVD system. The microstructural and phase analysis of developed TBCs will be presented. The CMSX-4 nickel superalloy was used as a base material. The platinum and palladium aluminide coatings were used as a standard type of bond coats. The newly developed Zr - modified aluminide coatings deposited by CVD method were used as well. The combination of CVD and EB-PVD using newly developed devices enables to cost reduction in TBCs production and increase of turbine blades lifetime.
AP8 Influence of Deposition Parameters on Structure of Diffusion Aluminide Coatings Obtained by CVD Method on Rene 108 DS Superalloy
Lucjan Swadzba, Bartosz Witala (Silesian University of Technology, Poland); Radoslaw Swadzba (Institute for Ferrous Metallurgy, Poland); Marek Hetmanczyk, Grzegorz Moskal, Boguslaw Mendala (Silesian University of Technology, Poland); Lukasz Komendera (AVIO Poland sp. z o.o., Poland)
Chemical vapor deposition (CVD) method plays meaningful role in deposition of aluminide coatings on nickel based superalloys. Owing 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 Rene 108 DS superalloy will be presented. Result of diffusion aluminizing using CVD apparatus built in Silesian University of Technology will be presented. An influence of technological parameters such as: temperature, pressure in retort, chemical composition of reactant gases on microstructure, thickness and phase composition of aluminide coatings will be described. Further processes were conducted using additional source granules consisting of Ni, Al, Cr and were modified by reactive elements. Aluminide coatings were investigated by light microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray diffraction analysis (XRD).
AP9 Research on High Temperature Property of Plasma Sprayed Lanthanum Cerium Oxide Thermal Barrier Coatings
Ruijun Wang, TieJun Wu, Weiping Wang (Beijing Aeronautical Technology Research Center, China)
With the development of aircraft gas turbine, requirement novel ceramic top coating material to improve temperature capability of thermal barrier coatings. In this paper, lanthanum cerium oxide (LCO) spray powder and plasma sprayed coatings high temperature properties was investigated. LCO spray powder keep phase stability at 1500℃. And the powder composition was not changed during thermal treatment. However, the content of Ce element in plasma sprayed coats decreased during thermal treatment at 1500℃. Spray power and exposure temperature has evident influence on plasma sprayed coats high temperature phase stability. Phase stability of plasma sprayed coat can be improved by reducing spray power.
AP10 Calcium-Magnesium Aluminosilicate (CMAS) Reactions and Degradation Mechanisms of Advanced Environmental Barrier Coatings
Nadia Ahlborg (The Ohio State University, US); Dongming Zhu (NASA Glenn Research Center, US)
Environmental barrier coatings (EBCs) are used to protect future Si-based ceramic matrix composite (CMC) turbine engine hot-section components from oxidation and corrosion and extend component lifetimes. Future high efficiency engines require significantly higher operating temperatures and reduced component cooling, leading to accelerated infiltration and reactions of ingested calcium-magnesium aluminosilicates (CMAS) sand and ash within the engine hot section components. This study primarily focuses on the reactions and degradation mechanisms between CMAS and several advanced EBC material systems, including rare earth (RE)-silicates Yb2SiO5, Y2Si2O7, and RE-oxide doped HfO2 and ZrO2 at 1500ºC. The microstructure and phase characteristics of CMAS-EBC specimens were examined using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Results showed that the CMAS dissolved RE-silicates to form crystalline, highly non-stoichiometric apatite phases. Cross-section images show that the CMAS deeply penetrated into the EBC grain boundaries and formed extensive grain boundary low-melting eutectic phases, causing grain boundary recession with increasing testing time in the silicate materials. The preliminary results also showed that CMAS reactions also formed low melting grain boundary phases in the higher concentration RE-oxide doped HfO2 systems. The effect of the test temperature on CMAS reactions of the EBC materials will also be discussed.The faster diffusion exhibited by apatite and RE-doped oxide phases and the formation of extensive grain boundary low-melting phases may limit the CMAS resistance of some of the environmental barrier coatings at high temperatures.
AP11 An Experimental Method for Determining the Mode II Interfacial Toughness of Thermal Barrier Coatings
Simon Lockyer-Bratton, Jaafar El-Awady, Kevin Hemker (Johns Hopkins University, US)
Experimentally measured interfacial fracture toughness is a critical parameter in determining the lifetime of thermal barrier coating (TBC) systems. Currently no reliable test method has been created to evaluate this property under pure Mode II conditions, which are most representative of critical TBC delamination upon turbine engine cool down. A newly developed compression edge delamination test sample has been employed to measure the strain energy release rate, G, associated with delamination between the bond coat and top coat under a nearly pure Mode II loading condition. The material systems tested consist of an electron beam physical vapor deposited (EBPVD) 7% yttria-stabilized zirconia (YSZ) top coat on either a 1) Pt-modified aluminide diffusion bond coat on a René N5 substrate or a 2) low pressure plasma spray (LPPS) NiCoCrAlY bond coat on a PW1484 substrate. Sample design as well as a unique sample fixture designed for use during the bond coat and top coat application processes are discussed. A detailed finite element model is used to evaluate the experimental results and show the effects of material layer properties and crack face friction on G.
AP12 Isothermal Oxidation of a Single Crystal N5 Superalloy in the Range of 1050°C to 1150°C
Radoslaw Swadzba (Institute for Ferrous Metallurgy, Poland); Bartosz Witala, Lucjan Swadzba (Silesian University of Technology); Lukasz Komendera (AVIO Polska)

The paper concerns behavior of Rene N5 2nd generation single crystal Ni superalloy during isothermal oxidation in dry oxygen at 1050°C, 1100°C and 1150°C for 100h. The oxidation tests were performed using Mettler Toledo apparatus for isothermal oxidation tests with high accuracy mass control. The mass change curves of the samples oxidized at 1050°C, 1100°C and 1150°C are presented along with corresponding microstructures. High resolution CTEM and S/TEM techniques were applied for a detailed characterization of oxide scales formed after 100h of oxidation at 1050°C, 1100°C and 1150°C for a direct comparison of the phase composition and chemistry of the oxides and the interfaces between them. High resolution S/TEM EDS elemental mappings were performed in order to study segregation of elements to grain boundaries of the alumina scales. The samples for S/TEM analysis were prepared using FIB (Focused Ion Beam).

AP13 Boron Distribution in High Temperature Silicide Coatings for Niobium Alloys: An Analytical Problem Which can be Solved using a Coupled WDS-EDS System
Sandrine Mathieu, Leo Portebois, Nabil Chaia (Université de Lorraine, France)

Progresses in the field of gas-turbine engine for aircraft are controlled by the availability of structural materials able to withstand higher-temperature hostile environments (very significant flow conditions containing aggressive elements such as water vapor, at more than 1150°C). The efficiency of intermetallic silicides Ti3X3CrSi6 (M7Si6-TiX with X=Fe,Co or Ni) as protective coatings (bond coats) for niobium alloys against oxidation was demonstrated through many works. These compounds are manufactured by halide activated pack-cementation technique. During oxidation tests, these coatings develop a duplex protective chromia /silica oxides scale. These refractory silicides present a ductile brittle temperature transition around 900-1000°C that led sometimes to the formation of cracks throughout the coatings. This behavior is mainly observed when the coated pieces endure rapid change of temperature, e.g, oxidation in cyclic conditions. Therefore boron was added in these coatings by the cementation way in order to increase the fluidity of silica and to obtain self-healing oxides scale.

Whatever the nature of the matrix around, boron is generally difficult to characterize both qualitatively and quantitatively using SEM and its associated analyses techniques (EDS and WDS spectrometry) based on X-ray emission because of the low rate of emission of this light element. In the present case, the complex chemical composition of the substrate (Nb, Ti, Hf, Fe, Cr, Si) renders still more difficult the characterization of boron because of the spectral interference which exists between the Nb (Mz) and B (Kα) X-ray. To separate both contributions, those of boron and niobium, a coupled WDS-EDS system was employed. Elaboration of boron containing standards was also required.

The present paper aimed at presenting the optimization of the analytical conditions that allowed the location of boron in the coating both post-manufacturing and post-oxidation tests.

AP14 Evaluation of EBPVD Top Coat Modulus Using Micro-beam Bending Techniques
Binwei Zhang, Kevin Hemker (Johns Hopkins University, US)

Layered thermal barrier coatings are widely used to protect underlying superalloy components from high temperature oxidation. Commercial systems are typically composed of a yittra-stabilized zirconia (YSZ) top coat, a thin thermally grown oxide (TGO), and an intermetallic bond coat on top of the superalloy substrate. Interfacial delamination between the top coat and the bond coat are often observed after cyclic thermal exposure, due in part to the stresses that arise from the mismatch of thermal expansion coefficients of the materials. To evaluate the thermally induced residual stress and predict resulting interfacial failure, the Young’s modulus of the top coat is of primary interest. In this study, micro-beam bending techniques for both attached and free-standing YSZ coatings has been developed to assess the as-deposited top coat modulus as a function of substrate geometry. A tension/compression asymmetrical behavior of top coat was observed, and finite element analysis was carried out to quantify the modulus values.