As operating temperatures of gas turbine engines increase, there is a need for superalloy turbine disks that can operate with rim temperatures in excess of 1300 F. To meet this need, a new generation of nickel-base superalloys, such as ME3, Alloy 10, and LSHR, has been developed. These alloys all contain a high percentage of gamma-prime precipitates, Ni3Al, and refractory element additions to achieve strength at temperature. Although they provide advantages over older alloys, the continuing need for high tensile strength at intermediate temperatures in the bore of a disk, which runs much cooler than the rim, as well as high creep strength in the rim also demands innovative heat treatments that can optimize bore and rim properties. Traditional heat treatments produce fine-grain disks when the solution temperature is maintained below the gamma-prime solvus and produce coarse-grain disks when the solution temperature is maintained above the gamma-prime solvus. Fine-grain disks yield high strength at intermediate temperatures, whereas coarse-grain disks yield high creep strength at elevated temperatures. Recently, several advanced heat-treatment technologies have been developed that can produce a superalloy disk with a fine-grain bore and a coarse-grain rim. Tradeoff studies by GE Aircraft Engines and Allison Advanced Development Company (AADC) have identified the potential advantages offered by superalloy disks that employ a dual grain structure for advanced gas turbine engine applications. The GE Aircraft Engines report cited reduced fatigue for a disk with a dual grain structure in comparison to a coarse-grain disk, whereas the AADC report cited a creep benefit for a disk with a dual grain structure in comparison to a fine-grain disk.

SOURCE: J. Gayda, T. P. Gabb, P. T. Kantzos. "Advanced Heat Treatment Technology for Superalloy Disks Verified." Research & Technology 2005. NASA/TM-2006-214016. (May 2006):135-136

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