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Effect of Local Recrystallized Grains on the Low Cycle Fatigue Behavior of a Nickel-Based Single Crystal Superalloy

1
Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, Zhuhai 519082, Guangdong, China
2
AML, School of Aerospace, Tsinghua University, Beijing 100084, China
3
Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
*
Authors to whom correspondence should be addressed.
Crystals 2019, 9(6), 312; https://doi.org/10.3390/cryst9060312
Received: 29 April 2019 / Revised: 11 June 2019 / Accepted: 11 June 2019 / Published: 18 June 2019
(This article belongs to the Special Issue Fundamentals of Superalloys)
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Abstract

This paper aims to understand the effect of local recrystallization (RX) on the low cycle fatigue fracture of a turbine-blade single crystal nickel-based superalloy. The fatigue life of the single crystal superalloy was evidently decreased by local recrystallization. In single crystal specimens, casting porosity is the preferential fatigue crack initiation site, which is followed by crystallographic crack propagation along one or several octahedral slip planes. For all RX specimens, fatigue cracks preferred to initiate from local recrystallized grains and propagated through the recrystallized grains in a transgranular manner, followed by crystallographic crack propagation in the substrate single crystal superalloy. Moreover, fatigue tests indicated that locally recrystallized specimens exhibited temperature dependent fracture modes, i.e., transgranular cracking dominated at 550 °C, whereas intergranular cracking was preferred at 850 °C. Evident oxidation of fracture surfaces and strength degradation of grain boundaries at 850 °C was evidenced by scanning electronic microscopic observations. The present study emphasized the need to evaluate the effect of recrystallization according to the working conditions of turbine components, i.e., the local temperature. View Full-Text
Keywords: nickel-based superalloy; fatigue; recrystallization; microstructure; temperature nickel-based superalloy; fatigue; recrystallization; microstructure; temperature
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Ma, X.; Jiang, J.; Zhang, W.; Shi, H.-J.; Gu, J. Effect of Local Recrystallized Grains on the Low Cycle Fatigue Behavior of a Nickel-Based Single Crystal Superalloy. Crystals 2019, 9, 312.

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