ICMCTF2002 Session A4-1: Coating Processes Technology Advancement

Wednesday, April 24, 2002 1:30 PM in Room Esquire/Towne

Wednesday Afternoon

Start	Invited?	Item
1:30 PM		A4-1-1 Sputter Deposition of Graded and Non-Graded NiCoCrAlY/Alumina/YSZ Coatings A.N. Sekfali, K.L. Choy, R.D. Rawlings, A. Selcuk (Imperial College of Science, Technology and Medicine, United Kingdom) Thermal barrier coatings are employed in turbine engines to coat turbine blades and other components in order to provide thermal insulation. However, their durability is affected by the existence of the thermally grown oxide and the thermal expansion mismatch between the metallic bond coat, thermally grown oxide and the ceramic topcoat. Consequently the concept of graded thermal barrier coatings has been introduced as one of the potential solution to overcome the problem. Graded and non-graded NiCoCrAlY-alumina-YSZ coatings have been deposited by magnetron sputtering. The effects of processing parameters (e.g. power density, sputtering pressure and dc bias) on the microstructure and properties of the deposited coatings have been studied. The coated samples have also been heated treated and subjected to thermal cycling in order to establish the durability of the coatings. A combination of techniques such as X-ray diffraction, scanning electron microscopy, Raman Spectroscopy, and Ruby Fluorescence have been used to characterise the microstructure, texture, crystal growth and stress levels of the deposited films. The results of such a work will provide a useful guideline for establishing the optimum functionally graded thermal barrier coating.
1:50 PM		A4-1-2 Conformable Eddy-Current Sensors for Condition Assessment of Gas Turbine Coatings A. Washabaugh, Y. Sheiretov, V. Zilberstein, D. Schlicker, N. Goldfine (JENTEK Sensors, Inc.) New advances in the use of conformable Meandering Winding Magnetometer (MWM) eddy-current sensors and arrays (MWM-Arrays) provide nondestructive inspection capabilities for condition monitoring of protective coatings on turbine blades. Metallic overlay coatings and thermal barrier coatings (TBCs), including a metallic bond coat and the ceramic topcoat, allow engine operation at higher temperatures and provide protection from severe oxidation and high-temperature corrosion for turbine blades and vanes. Effective condition monitoring, remaining life assessment and crack detection are essential to address both safety and cost concerns; however, this monitoring requires accurate and practical nondestructive methods that provide relevant information about thickness and degradation of the coatings as well as degradation of the substrate and detection of local anomalies such as cracks. An NDE method for inspecting these coatings using spatially periodic conformable eddy-current sensors, such as the MWM, and quantitative model-based inversion algorithms is described in this paper. For TBCs, multiple frequency measurements and data inversion methods provide simultaneous and independent determination of multiple unknowns, such as metallic bond coat thickness, metallic bond coat porosity, and ceramic topcoat thickness for TBC manufacturing quality control. Also, model-based methods have been applied to thermally aged samples for estimation of beta depletion zone thickness and other representative features of coating degradation. Ongoing work is aimed at inspection of magnetizable materials, in both as-manufactured and aged conditions, and the detection, imaging and characterization of cracks in the substrate and/or coating using high-resolution imaging MWM-Arrays. This paper provides a brief review of MWM technology, a description of improved multiple frequency quantitative inversion methods, and representative measurements on both as-manufactured and aged coating systems.
2:10 PM		A4-1-3 The Manufacture and Fatigue Cracking Resistance of Grit Free Aluminide Diffusion Coatings B.M. Warnes, A.L. Purvis (Howmet Research Corporation); J.E. Schilbe (Howmet Thermatech Coatings) Grit blasting is an inexpensive and effective means of removing shell material from super alloy castings, and of roughening the surface of super alloy castings prior to platinum electroplating or overlay coating deposition. However, some of the abrasive particles become imbedded in the surface of the super alloy during blasting operations, and this imbedded grit can have detrimental effects on the mechanical properties of gas turbine components. A research program was conducted to evaluate the use of molten caustic immersion to eliminate entrapped grit particles, and to determine the effects of entrapped grit removal on the Thermo-Mechanical Fatigue (TMF) crack resistance of aluminide diffusion coatings. The research program is described, the results are presented and discussed and all possible conclusions are summarized.
2:30 PM		A4-1-4 Use of Cathodic Arc Physical Vapor Deposition for Aerosapce Tribological Solutions R. A. Beers (Pratt & Whitney) Development within United Technologies has occurred for a variety of coatings to meet unusual tribological challenges. These coatings have benefited from the inherent properties of the cathodic arc process, as well as from creative application of existing materials. Materials deposited include both soft anti-fretting wear coatings as well as extremely hard metallic/carbide dispersion strengthened materials. The cathodic arc process has allowed for deposition of coatings onto very thin sheetmetal structures without detrimental effects associated with heavy grit blasting and severe thermal transients from thermal spray processes. Deposition conditions as well as applications will be discussed.
2:50 PM		A4-1-5 Improved Alumide/MCrAlY Coatings Systems for Super Alloys Using CVD Low Activity Aluminizing B.M. Warnes (Howmet Research Corporation) Chemical Vapor Deposition (CVD) low activity aluminizing was used to manufacture duplex diffusion aluminide (with or without platinum) / MCrAlX coatings for suepr alloy gas turbine engine components. Bulk chemcial analysis of aluminized MCrAlX foils indicated that the CVD low activity process removes potentially harmful elements (such as chromium, sulfur and phosphorus) from the MCrAlX during aluminizing, while pack cementation increased the concentrations of some impurities. The cyclic oxidation resistance of duplex coatings (aluminide / MCrAlX) made using pack cementation aluminizing and CVD low activity aluminizing was compared. Oxidation test results demonstrate the CVD aluminide / MCrAlX coating system exhibited much better oxidation resistance than a similar duplex coating system made using pack cementation. The experimental program is outlined, plus the experimental results are presented and discussed.
3:10 PM		A4-1-6 Preparation, Microstructural and Electrical Characterization of La_1-x√subxMnO₃₊δ Thin Films Synthesized via a Polymeric Route M. Gaudon, C. Laberty-Robert, F. Ansart, A. Rousset (CIRIMAT, University Paul Sabatier, France); P. Stevens (EDF, France) Solid oxide fuel cells (SOFCs) are electrical energy conversion devices with high efficiency and low pollution. In order to increase performances of SOFCs at intermediate temperature (700°C-800°C) and to decrease materials cost, an alternative solgel synthesis method has been investigated to deposit Lasub1-x√sub xMnO₃₊δ(LSMx) as cathode thin films. Polycrystalline LSMx thin films were prepared by dip-coating using a polymeric solution. Lanthanum, strontium and manganese nitrates were used as raw materials. The viscosity of the solution was adjusted at 60 cP and the ionic concentration of salts was 0.4 mol.L^-1. From these gels, films were deposited on polycrystalline ZrO₂8%Y₂O₃ceramics. Prior to experiments, the substrate Film thicknesses were adjusted with the number of layers. Roughness, adherence, porosity and grain size of mono or multilayers were evaluated. Typical thickness of monolayer is 250 nm. A key parameter in the multilayer process was the intermediate calcination temperature (400°C, 700°C or 1000°C) before each further layer deposition. A correlation between this intermediate temperature, morphology, thickness and porosity has been found ; porosity is ranging from 0 to 40% and thickness can reach 1µmfor multilayers. Electrical properties of LSMx films have been measured as a function of the strontium content x. LSMx films have a semiconductor behaviour above room temperature. Then, conductivities have been correlated with strontium content, thickness and intermediate temperature. The best results were obtained for LSM0.4 multilayers.