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Title: Long-Term Phase Instability in Water-Quenched U-6Nb

Abstract

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 (WQ-U6Nb) 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 agingmore » 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 sequence of WQ-U6Nb, and it leads to order-disorder transformation, precipitation hardening, and ductility embrittlement of WQ-U6Nb alloy.« less

Authors:
;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
895078
Report Number(s):
UCRL-CONF-218278
TRN: US200702%%599
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Presented at: 15th Biennial Conference on Nuclear Explosive Design Physics Conference, Livermore, CA, United States, Oct 17 - Oct 21, 2005
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE; AGE HARDENING; AGING; ALLOYS; AMBIENT TEMPERATURE; DUCTILITY; EMBRITTLEMENT; INSTABILITY; MICROHARDNESS; MICROSTRUCTURE; MODULATION; NUCLEAR EXPLOSIVES; ORDER-DISORDER TRANSFORMATIONS; PHYSICS; PRECIPITATION HARDENING; TRANSFORMATIONS; WAVELENGTHS

Citation Formats

Hsiung, L L, and Zhou, J. Long-Term Phase Instability in Water-Quenched U-6Nb. United States: N. p., 2006. Web.
Hsiung, L L, & Zhou, J. Long-Term Phase Instability in Water-Quenched U-6Nb. United States.
Hsiung, L L, and Zhou, J. Mon . "Long-Term Phase Instability in Water-Quenched U-6Nb". United States. doi:. https://www.osti.gov/servlets/purl/895078.
@article{osti_895078,
title = {Long-Term Phase Instability in Water-Quenched U-6Nb},
author = {Hsiung, L L and Zhou, J},
abstractNote = {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 (WQ-U6Nb) 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 sequence of WQ-U6Nb, and it leads to order-disorder transformation, precipitation hardening, and ductility embrittlement of WQ-U6Nb alloy.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 16 00:00:00 EST 2006},
month = {Mon Jan 16 00:00:00 EST 2006}
}

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