Microstructural extremes and the transition from fatigue crack initiation to small crack growth in a polycrystalline nickel-base superalloy

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• 作者：Jiashi Miao^a ; ^{miaojias@umich.edu} ; Tresa M. Pollock^b ; J. Wayne Jones^a
• 关键词：Fatigue crack initiation ; Superalloy ; Small crack growth ; Grain cluster ; 危3 Twin boundary
• 刊名：Acta Materialia
• 出版年：2012
• 期刊代码：1_13596454
• 类别：ms
• 出版时间：April, 2012
• 卷：60
• 期：6-7
• 页码：2840-2854
• 文件大小：4418 K

摘要

The fatigue behavior of the nickel-base superalloy Ren茅 88 DT has been investigated at room temperature with fully reversed loading in an ultrasonic fatigue apparatus operating at a frequency close to 20 kHz. A characterization protocol based on the electron backscatter diffraction technique has been developed to identify the combination of microstructural features within crack initiation sites and surrounding neighborhoods that leads to the transition from initiation to early small crack growth. Surface grains that were more than three times the average grain size, that were favorably oriented for cyclic slip localization and that also contained 危3 twin boundaries inclined to the loading axis were most favorable for fatigue crack initiation. Fatigue cracks subsequently grew in grain clusters within which grains are misoriented by less than 20掳 relative to the initiation grains. More highly misoriented neighboring grains resulted in crack arrest. The material characteristics that promote crack initiation and small crack growth exist only at the extreme tails of the microstructural distributions. The implications for modeling of fatigue life and fatigue life variability are discussed.