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Crystallinity Degradation Caused by Alloying Elements Diffusion During Creep of Ni-Base Superalloy

[+] Author Affiliations
Ken Suzuki, Takuya Murakoshi, Hideo Miura

Tohoku University, Sendai, Japan

Paper No. IMECE2015-53722, pp. V014T11A036; 5 pages
  • ASME 2015 International Mechanical Engineering Congress and Exposition
  • Volume 14: Emerging Technologies; Safety Engineering and Risk Analysis; Materials: Genetics to Structures
  • Houston, Texas, USA, November 13–19, 2015
  • Conference Sponsors: ASME
  • ISBN: 978-0-7918-5757-1
  • Copyright © 2015 by ASME


High temperature mechanical properties of Ni-base superalloys are improved by the fine cuboidal γ’ (Ni3Al) precipitates orderly-dispersed in the γ matrix (Ni-rich matrix) because the dispersed texture in a grain inhibits dislocation motion. However, it is well known that directional coarsening of the γ’ precipitates perpendicular to a principal stress occurs not only during creep loading but also during cyclic loading and, the formation of the raft causes the decreasing of high temperature strength drastically. Therefore, it is very important to evaluate the damage of the alloys caused by creep and fatigue loading based on the change of their micro texture. In this study, the change of crystallinity of the Ni-base superalloys (CM247LC) under creep loading was analyzed by applying Electron Back-Scattered Diffraction (EBSD) method. The image quality (IQ) value obtained from the EBSD analysis was used for the quantitative evaluation of the crystallinity in the area where an electron beam of 10 nm in diameter was irradiated. The quality of the atomic alignment of both γ’ and γ phases was found to degrade with increasing creep damage. The degradation of crystallinity suggests that the ordered L12 structure of Ni3Al became disordered and the density of dislocations and vacancies increased. However, KAM (Kernel Average Misorientation) value did not change significantly with increasing creep damage. Therefore, the dominant factor of the creep damage of this alloy is the strain-induced diffusion of elements under loading, and the decrease of the crystallinity.

Copyright © 2015 by ASME



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