On the Mechanical Behavior of a New Single-Crystal Superalloy for Industrial Gas Turbine Applications
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NEW nickel-based superalloys are needed for hot section components, e.g., turbine blades and guide vanes, in the next-generation gas turbine engines required for power generation applications. Significant demands will be placed on these materials. For instance, excellent resistance to environmental attack is required, since the operating conditions and fuels used for these applications induce oxidation and corrosion; thus, the superalloys used will be distinct from those currently employed for aeroengine applications. Moreover, they must withstand the large mechanical loads necessary for efficient extraction of mechanical energy from the hot gas stream. Hence, creep[1,2] and fatigue[3,4] must be resisted. Recently, a new grade of single-crystal superalloy was developed for such applications, which displays a good balance of environmental and mechanical properties.[5,6] Its Cr content (at 15 wt pct) is substantially greater than for existing single-crystal superalloys, which improves significantly the resistance to oxidation and corrosion.[7] This article is concerned with the mechanical performance of this new single crystal superalloy. In common with most precipitation-hardened systems, the proper[1,2]
ATSUSHI SATO, Postdoctoral Student, and ROGER C. REED, Professor, are with the Department of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom. Contact e-mail: [email protected] JOHAN J. MOVERARE, Associate Professor, is with the Division of Engineering Materials, Department of Management and Engineering, Linko¨ping University, 58183 Linko¨ping, Sweden. MAGNUS HASSELQVIST, Specialist, is with Siemens Industrial Turbomachinery AB, 61283 Finspa˚ng, Sweden. Manuscript submitted January 31, 2011. Article published online January 19, 2012 2302—VOLUME 43A, JULY 2012
ties displayed will depend in a sensitive fashion upon the microstructure developed during heat treatment; for this class of material, hardening is by the gamma prime (c¢) phase and thus conditioning of the microstructure at temperatures in and around the c¢ solvus is expected to influence the mechanical properties displayed. Two distinct forms of mechanical response are studied as a function of the heat treatment applied: first, creep deformation, which is important due to the centrifugal loading experienced by the turbine blades in the engine;[1,2] and, second, thermomechanical fatigue (TMF), which is relevant particularly for smaller (aeroderivative) industrial gas turbines (IGTs) because of the interaction of thermal and mechanical strains arising from engine startup/cooldown.[8,9] As mission requirements become more demanding, it is becoming apparent that the performance of the material under TMF conditions can be life limiting; however, historically, very much more attention has been paid to the provision of creep resistance.[10] This is probably due to the significant extra difficulty imposed by the constraints of TMF testing; nonetheless, this situation needs to be corrected. Here, it is demonstrated tha
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