Spinodal Ordering and Precipitation in U-6 wt% Nb
Conference
·
OSTI ID:891382
A combinative approach of microhardness testing, tensile testing, and TEM microstructural analysis was employed to study the microstructure and mechanical instability of a water-quenched U-6wt.% Nb (WQU6Nb) alloy subjected to different aging schedules including artificial aging at 200 C, 15-year natural aging at ambient temperatures, and 15-year natural aging followed by accelerative aging at 200 C. The changes in mechanical property during and after the aging processes were examined using microhardness and tensile-testing methods. During the early stages of artificial aging at 200 C, the microhardness of WQ-U6Nb alloy increased, i.e., age hardening, as a result of the development of nanoscale modulation caused by spinodal decomposition. Coarsening of the modulated structure occurred after a prolonged aging at 200 C for 16 hours, and it led to a decrease of microhardness, i.e., age softening. Phase instability was also found to occur in WQ-U6Nb alloy that was subjected to a 15-year natural aging at ambient temperatures. The formation of partially ordered domains resulting from a spinodal modulation with an atomic-scale wavelength rendered the appearance of swirl-shape antiphase domain boundaries (APBs) observed in TEM images. Although it did not cause a significant change in microhardness, 15-year natural aging has dramatically affected the aging mechanisms of the alloy isothermally aged at 200 C. Microhardness values of the NA alloy continuously increased after isothermal aging at 200 C for 96 hours as a result of the phase decomposition of partially ordered domains into Nb-depleted {alpha} phase and Nb-enriched U{sub 3}Nb ordered phase in the alloy. It is concluded that the long-term natural aging changes the transformation pathway of WQ-U6Nb, and it leads to order-disorder transformation and precipitation hardening of WQ-U6Nb alloy.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 891382
- Report Number(s):
- UCRL-CONF-217871
- Country of Publication:
- United States
- Language:
- English
Similar Records
Microstructure and Mechanical Instability of Water-Quenched U-6wt% Nb Alloy Affected by Long-Term Aging
Long-Term Phase Instability in Water-Quenched U-6Nb
Spinodal Decomposition and Order-Disorder Transformation in a Water-Quenched U-6wt%Nb Alloy
Technical Report
·
Mon Dec 05 23:00:00 EST 2005
·
OSTI ID:889977
Long-Term Phase Instability in Water-Quenched U-6Nb
Conference
·
Sun Jan 15 23:00:00 EST 2006
·
OSTI ID:895078
Spinodal Decomposition and Order-Disorder Transformation in a Water-Quenched U-6wt%Nb Alloy
Technical Report
·
Tue Sep 12 00:00:00 EDT 2006
·
OSTI ID:900131