Additive Manufacturing of IN100 Superalloy Through Scanning Laser Epitaxy for Turbine Engine Hot-Section Component Repai
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GAS turbine hot-section components represent one of the most severe applications for high-temperature materials. Continuous demand for improvement of gas turbine efficiency has driven research efforts on new compositions and fabrication methodologies for superalloys capable of withstanding increasingly higher service temperatures. Over the past 30 years, the peak operating temperature of gas turbine hot-section components has increased from 1255 K to 1700 K (982 C to 1427 C) (1800 F to 2600 F). This development has posed serious design challenges from the thermal cooling and fatigue strength aspects, and different approaches have been pursued to meet these challenges. The RANADIP ACHARYA, formerly with the George W. Woodruff School of Mechanical Engineering at the Georgia Institute of Technology, 801 Ferst Dr., Atlanta, GA 30332-0405, is now with United Technologies Research Center, East Hartford, CT. SUMAN DAS, Professor and the Morris M. Bryan, Jr. Chair, is with the George W. Woodruff School of Mechanical Engineering at the Georgia Institute of Technology, and also with the School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Dr. NW, Atlanta, GA 30332-0405. Contact email: [email protected] Manuscript submitted December 31, 2014. Article published online April 28, 2015 3864—VOLUME 46A, SEPTEMBER 2015
principal approach has involved improvement of the creep strength and fatigue resistance of the material, allowing operation of the turbine at higher temperatures. This approach is used in the aviation industry requiring the use of novel and improved superalloys.[1] However, the operational life of the gas turbine hotsection components decreases due to several reasons. Firstly, increased cooling effectiveness achieved with the advanced air cooling and steam cooling schemes produces higher thermal gradients in hot-section turbine components. This significantly increases the thermal strain associated with these parts, and the thermal cycle associated with the strain causes severe fatigue loading. The creep strength and fatigue resistance of the superalloys are improved by incorporating secondary phase precipitates or c¢ in the FCC Ni or c matrix. The presence of secondary c¢ phases forms an anti-phase boundary and locks the disassociated or partial dislocation movement.[2,3] The secondary phases also increase the susceptibility to cracking. Additionally, the turbine blades still have a limited operating life due to material loss at the blade tip resulting from the abrasion between the blade and the engine shroud. Once a blade has experienced a certain amount of material loss (typically on the order of 0.5 to METALLURGICAL AND MATERIALS TRANSACTIONS A
1 mm on an 8 cm tall blade), it cannot be used any further and has to be scrapped since the superalloys involved are ‘non-weldable.’ Different forms of cracking present obstacles in the repair or processing of Ni-base superalloy components. The crack mechanisms can be primarily distinguished as solidification cracking, grain boundary liqua
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