期刊
ACTA MATERIALIA
卷 60, 期 6-7, 页码 2840-2854出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2012.01.049
关键词
Fatigue crack initiation; Superalloy; Small crack growth; Grain cluster; Sigma 3 Twin boundary
资金
- Air Force Office of Scientific Research [F49620-03-1-0069]
- DARPA
- Rackham Predoctoral Fellowship Program
The fatigue behavior of the nickel-base superalloy Rene 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 Sigma 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 degrees 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. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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