The role of coincidence-site-lattice boundaries in creep of Ni-16Cr-9Fe at 360 C
- Univ. of Michigan, Ann Arbor, MI (United States)
The objective of this study is to understand and quantify the role of the coincidence-site-lattice boundary (CSLB) population on creep deformation of Ni-16Cr-9Fe at 360 C. It is hypothesized that an increase in the CSLB population decreases the annihilation rate of dislocations in the grain boundary, leading to an increase in the internal stress and a decrease in the effective stress. The result is a reduction in the creep strain rate. The role of CSLBs in deformation is, thus, to increase the internal stress by trapping run-in lattice dislocations at the grain boundaries as extrinsic grain boundary dislocations (EGBDs), creating backstresses on following dislocations rather than annihilating them, as in the case of high-angle boundaries (HABs). The hypothesis was substantiated by showing (1) that dislocation absorption kinetics differ substantially between a CSLB and an HAB, and (2) that the CSLB fraction strongly affects the internal stress in the solid. Steady-state creep rates of Ni-16Cr-9Fe in 360 C argon were also found to be strongly affected by the grain boundary character distribution. Increasing the CSLB fraction by approximately a factor of 2 resulted in a decrease in steady-state creep rates by a factor of 8 to 26 in coarse-grain (330 {micro}m) samples and a factor of 40 to 66 in small-grain (35 {micro}m) samples. It is postulated that annihilation of EGBDs only occurs at triple lines where at least two HABs intersect. By using a geometric relationship to evaluate the probability of EGBDs annihilating at a triple line, the model predicts a non-linear dependence of the creep rate with CSLB fraction, yielding excellent correlation with measurement. The model provides a physical basis for measurements which show that increasing the CSLB fraction by only moderate amounts can greatly reduce the steady-state creep rate in Ni-16Cr-9Fe.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG02-85ER45184
- OSTI ID:
- 543485
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Vol. 28, Issue 10; Other Information: PBD: Oct 1997
- Country of Publication:
- United States
- Language:
- English
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