Aging and phase stability of waste package outer barrier
- LLNL
After aging for 16,000 hr at 593 C, P phase was found at Alloy 22 grain boundaries. At higher temperatures (as much as 760 C for the same aging time), both {mu} and P phase formed on grain boundaries and within the grains. Grain boundary carbides also form at 593 C and higher, but the amount of carbide is small compared to the p and P phases. A small amount of sigma phase forms in Alloy 22 after 16,000 hr at 704 and 760 C. LRO was seen after aging for 16,000 hr at 593 C and for 40,000 hr at 427 C, but ordering most likely begins at shorter times. More work must be done in phase identification. Samples aged at times less than 16,000 hr must be examined so that the phase evolution during aging can be determined. A procedure being developed for phase extraction and x-ray diffraction should make phase identification and quantification of the relative amounts of each phase easier. The times at which various stages of intermetallic precipitation occur in Alloy 22 base metal displayed an exponential (Arrhenius-type) temperature dependence. The activation energy was determined to be 290 kJ/mol. A more quantitative model based on precipitate volume fraction measurements that can be integrated over a variable temperature profile must be developed before a reasonable prediction of the phase stability of Alloy 22 base metal under repository conditions can be made. In addition, the effect of intermetallic and carbide precipitation on Alloy 22 properties must be determined. Precipitation kinetics in weld heat-affected zones, as well as in the base metal, must be studied because the thermal pulse given the HAZ during the welding process may alter nucleation of intermetallics and therefore the precipitation kinetics. Intermetallic and carbide precipitates form in Alloy 22 welds during the welding process. It will be verified that these phases do not have a detrimental effect on the relevant weld properties. The effect of aging on the precipitate volume fraction and average size and on weld properties must also be determined.
- Research Organization:
- Lawrence Livermore National Lab., CA (US)
- Sponsoring Organization:
- USDOE Office of Defense Programs (DP) (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 14686
- Report Number(s):
- UCRL-ID-134582
- Country of Publication:
- United States
- Language:
- English
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