Abstract
The relative importance of the vacancy and interstitial contributions to radiation-induced segregation (RIS) in Fe-Cr-Ni alloys is studied to better understand the mechanisms causing changes in grain boundary composition and to improve the capability to predict RIS in austenitic Fe-Cr-Ni alloys. The primary driving mechanism for segregation in Fe-Cr-Ni alloys is shown to be the inverse Kirkendall (IK) mechanism, specifically the coupling between alloying elements and the vacancy flux. To study grain boundary segregation, seven alloys were irradiated with 3.2 MeV protons at temperatures from 200°C to 600°C and to doses from 0.1 to 3 dpa. Grain boundary compositions were measured using both Auger electron spectroscopy (AES) and scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM/EDS). Grain boundary compositions were compared to model predictions that assume segregation was driven either by preferential interaction of solute atoms with the vacancy flux alone or in combination with binding of undersized solutes to the interstitial flux. Calculations that assume the segregation is caused by preferential interaction of solute atoms with the vacancy flux generally followed the trends of the segregation measurements. However, the inclusion of interstitial binding to the IK model causes poor agreement between model predictions and segregation measurements, resulting in severe overprediction of Ni enrichment and Fe depletion. Comparisons of segregation models with RIS in alloys irradiated with neutrons also show that preferential interaction of solutes with the vacancy flux sufficiently describes segregation in Fe-Cr-Ni alloys.
| Original language | English |
|---|---|
| Pages (from-to) | 44-58 |
| Number of pages | 15 |
| Journal | Journal of Nuclear Materials |
| Volume | 255 |
| Issue number | 1 |
| DOIs | |
| State | Published - May 1998 |
| Externally published | Yes |
Funding
The authors gratefully acknowledge P.L. Andresen at the General Electric for supplying the sample alloys and the bulk chemical analysis. We are grateful to J.M. Cookson and J. Gan for assistance in performing sample irradiations and to the Michigan Ion Beam Laboratory at the University of Michigan for the use of the irradiation facilities. We also thank the Surface Analysis Laboratory at the Ford Motor Research and Development Center for the use of their PHI 660 Scanning Auger Microprobes. Additional thanks go to the Electron Microbeam Analysis Laboratory and staff at the University of Michigan. Finally, thanks go out to S.M. Bruemmer at Pacific Northwest Laboratory for his support. This research was supported by the US Department of Energy under grant DE-FG02-93ER-12310, by the Associated Western Universities-Northwest under US Department of Energy grant DE-FG02-89ER-7552, and by the Southeast Universities Research Association through the SURA/ORNL summer research program. Research partially supported by the Division of Materials Sciences, US Department of Energy under contract DE-AC05-96OR22464 with Lockheed Martin Energy Research, and through the SHaRE Program under contract DE-AC05-76OR00033 with Oak Ridge Associated Universities. Partial support for T.R.A. was provided by a National Science Foundation Graduate Fellowship.