U-Nb aging final report
A survey of U-Nb aging studies showed that age hardening through diffusional phase-separation is the most likely mechanism responsible for aging related property changes in banded U-6Nb components. The findings of recent transmission electron microscopy and atom probe tomography investigations are consistent with diffusional phase-separation on a scale of <3 nm in the martensitic matrix phase. Phenomenological studies of mechanical property responses to aging of nonbanded U-5.6Nb and U-7.7Nb showed that the second yield strength and total elongation were the most suitable age-sensitive properties from which relevant activation energies Q for aging at low temperatures could be determined. The derived Q values, 25–30 kcal/mole, are in good agreement with previous surveys of U-Nb aging data and were used for lifetime predictions. Lifetime predictions at various storage temperatures were made through extrapolation of second yield strength and total plastic elongation artificial-aging data. The output was a range of lifetimes spanning decades to thousands of years, predicated with several key assumptions and the use of a rudimentary failure criterion. Consistent with previous aging analyses, there is a potential for unacceptable ductility degradations during the expected service lifetimes of high-Nb (7–8 wt%) regions in the banded WR U-6Nb components stored above certain temperatures. Age-related ductility degradations in regions close to the mean alloy composition, 5.5–6 wt% Nb, were determined to be of no concern. Given the lack of knowledge concerning the quantitative linkages between easily measured aging-related property changes and their impact on performance, it is unclear whether aging degradations resulting in unacceptable performance of stockpiled U-6Nb will actually occur on time scales of interest. However, historical experience with LLNL U-6Nb components indicates that aging of LANL U-6Nb components will not be significant enough to affect performance on the decades-long time scales of interest, at least at lower storage temperatures. Information and insights from future studies will result in modification of these lifetime predictions either upward or downward.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA)
- DOE Contract Number:
- AC52-06NA25396
- OSTI ID:
- 1820470
- Report Number(s):
- LA-14327
- Country of Publication:
- United States
- Language:
- English
Similar Records
Property and lifetime prediction in aged U-Nb alloys: a statistical assessment
Microstructure and Mechanical of U-6Nb and U-8Nb in Gamma Quenched and Long-Term Aged Conditions