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Room: Salon 3
Location: Clarion Plaza Hotel
Session Chairman: Dr. N.S. Cheruvu, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228
8:30 am INVITED
STATUS, ISSUES AND CHALLENGES OF MATERIALS FOR ADVANCED LAND BASED GAS TURBINES: B.B. Seth, Westinghouse Electric Corporation, Orlando, FL 32826-2399
Abstract not available.
9:20 am DEVELOPMENT OF DIRECTIONALLY SOLIDIFIED BLADES AND VANES FOR LAND BASE TURBINE: Hisataka Kawai, Kohji Takahashi, Ikuo Okada, Taiji Trigoe, Akira Mitsuhashi; Mitsubishi Heavy Industries, Ltd, Takasago Research & Development Center, 2-1-1 Shinhama Arai-Cho, Takasago, Hygo Pref. 676 JAPAN; Mitsubishi Materials Corporation, 1-297 Kitabukuro-Cho Omiya, Saitama 330, Japan
Directionally solidified blades and vanes, so-called DS blades and vanes, have already been used in jet engines, but seldom in land-base gas turbines, because there are large differences in the size of hot parts, fuel and so on between jet engines and land-base gas turbines. It is necessary to take these differences into account when developing DS blades and vanes for land-base gas turbines. Mitsubishi Heavy Industries, Ltd. started to develop DS blades some years ago. First, material properties, such as, tensile strength, creep rupture, fatigue, other physical properties, etc, were investigated. Then, the optimization of casting conditions for large size blades (501FG/T 1st blade) was conducted. Finally, actual DS blades were cast and it was confirmed their material properties were excellent. Also their machinability and coating were evaluated and good results were obtained. As a result, DS blades were installed in an actual gas turbine (MF111G/T) in January 1994 which have been in operation since then.
MICROSTRUCTURAL STABILITY OF ADVANCED SINGLE CRYSTAL SUPERALLOYS: W.S. Walston, GE Aircraft Engines, 1 Neumann Way, M85, Cincinnati, OH 45215
Microstructural stability is a key parameter in the development and application of single crystal superalloys. The formation of topologically close packed (TCP) phases occurs to some degree in most single crystal superalloys. The effect of these phases on properties will be discussed. In addition, the effects of time and temperature on the formation of TCP phases will be shown for a recent single crystal superalloy, René N6. Another form of microstructural instability has recently been observed in high refractory content single crystal superalloys. This instability, termed SRZ, is a cellular phase transformation that can occur either beneath coatings or in the alloy substrate. The occurrence and effects of this instability in various alloys will be discussed. The third form of microstructural instability observed in several single crystal superalloys is the conversion of the matrix with 1 precipitates to a microstructure with a continuous phase. Several examples of this behavior will be shown. The relationship between this form of instability, rafting and creep rupture properties will also be discussed.
10:00 am BREAK
THE EFFECT OF CAST SIZE ON HOT CORROSION RESISTANCE OF SINGLE CRYSTAL NICKEL BASED SUPERALLOY CMSX-4: Ming Li, V. Desai, Mechanical Materials and Aerospace Engineering Department, University of Central Florida, Orlando, FL 32816; N.S. Cheruvu, Southwest Research Institute, 6220 Culebra Road, San Antonio TX 78228
Advanced single crystal (SC) nickel based superalloys have been available in small cast size for aero engine applications for a long time. Where as the SC techniques are not yet widely used in the land based engine components because of their much larger size which makes casting and the subsequent heat treatment more difficult. The difference in defects, such as microporosity, segregation, /1 eutectic, and dendritic structure, derived from casting size differences will affect the heat treatment process and the subsequent service properties, including hot corrosion/oxidation behavior. Hot corrosion tests were carried out at 900, 950, and 1000°C on specimens coated with NasSO4 in air. Three different kinds of specimens; as-cast and heat treated CMSX-4 from small and large blades, and IN738, were used to study the effects of cast defects and heat treatment on hot corrosion behavior and to compare the hot corrosion resistance of the single crystal superalloy with a typical land based turbine material. The corrosion product morphology, microstructure and composition were investigated using metallography and SEM/EDS. It is concluded that although the hot corrosion resistance of this single crystal material is not as good as that of IN738, proper heat treatment can double its hot corrosion resistance.
RELIABILITY OF A SINGLE CRYSTAL NIAL ALLOY FOR GAS TURBINE APPLICATIONS: R. D. Noebe, J. Salem, J. Manderscheid, NASA Lewis Research Center, M.S. 24-1, Cleveland, OH 44135; R. Darolia, General Electric Aircraft Engine Co., Cincinnati, OH 45215
Due to numerous property advantages, NiAl single crystal alloys are being investigated as a replacement for Ni-based single crystal superalloys in high pressure turbine engine sections, however, the current drawback is their lack of ductility. Consequently, a significant effort is being made to develop testing and design methodologies that will account for this lack of ductility. The present approach is to modify existing test methods and brittle design methodologies, such as those in the Ceramic Analysis and Reliability Evaluation of Structures (CARES) code, and to experimentally verify the results. To this end, the statistical nature and source of fracture in a high-strength, single crystal NiAl alloy has been studied via flexural testing of 3- and 4-point bend specimens of various crystallographic orientations. Flexural strength results indicate a wide dispersion in strength that can be characterized via normal or Weibull statistics. While the fracture strength was function of orientation, the Weibull modulus was not. Failure origins were determined for most of the specimens tested. In all cases, failure occurred from singular carbide particles or machining damage. It was also determined that the Weibull scaling law applies to uniaxial cases for effective surface area changes of 300% or less.
EFFECT OF SOLUTION HEAT TREATMENT ON DS TRANSVERSE STRENGTH: H. Tamaki, A. Yoshinari, A. Okayama, N. Watanabe, M. Kobayashi, Hitachi Research Laboratory, Hitachi, Ltd., Hitachi, Ibaraki, Japan
It is well known that creep-rupture strength of nickel-base superalloys strongly depends on the conditions of solution heat treatment. Jackson et al. 1 showed that creep-rupture life of MAR M 200 Hf DS in longitudinal direction increased with increasing volume fraction of fine 1 upon solution heat treatment. On the other hand, Cetel and Duhl 2 showed that creep ductility of PWA1426 DS in transverse direction decreased with increasing volume fraction of fine 1. In this study, in order to investigate the effect of solution heat treatment on DS transverse strength, CM186LC DS which is usually used without solution heat treatment was solution heat treated at 1548K for different time periods. Results are summarized as follows. (1) Creep-rupture strength of CM186LC DS in longitudinal direction increased by solution heat treatment. (2) Creep-rupture strength of CM186LC DS in transverse direction decreased by solution heat treatment. (3) Boron at grain boundaries diffused into grains by solution heat treatment. This phenomenon possibly caused the decrease of creep-rupture strength of CM186LC DS in transverse direction.
ALLOY 603GT: A NEW COBALT FREE ALLOY FOR GAS TURBINE COMPONENTS: D.C. Agarwal, 11210 Steeplecrest Dr. #120, Houston, TX 77065-4939; U. Brill, Krupp-VDM GmbH, Werdohl, Germany
Modern gas turbine components must possess unique combination of various high temperature strength and corrosion resistance properties for providing increased efficiency and reliability of operation. Some of these properties, which a material must have are good isothermal and cyclic oxidation resistance, good carburization resistance, good thermal stability, good stress rupture and fatigue strength and most importantly, good fabricability and weldability. Alloy 603GT is a new cobalt free nickel base alloy especially developed for modern gas turbine components. Its basic composition of high chromium, high aluminum, high carbon (25 Cr, 2.6 Al, 0.3 C, 0.1 Y, 9 Fe, Ni balance) and micro alloying with titanium and zirconium, gives this alloy a unique combination of excellent high temperature strength and superior oxidation resistance, carburization resistance, good thermal stability, grain growth resistance and spallation resistance. It's development, properties and cost effectiveness are discussed.
MECHANICAL PROPERTY COMPARISON OF SELECTED NICKEL BASE SUPERALLOYS FOR LAND BASED GAS TURBINE APPLICATIONS: Colin Thomas, Howmet Corporation, Whitehall, MI 49445
Abstract not available.
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