Hostname: page-component-78c5997874-v9fdk Total loading time: 0 Render date: 2024-11-17T15:14:04.356Z Has data issue: false hasContentIssue false
  • English
  • Français

Spinodal ordering and precipitation in U-6wt%Nb

Published online by Cambridge University Press:  26 February 2011

Luke Lieh-Ming Hsiung  and
Jikou Zhou
Luke Lieh-Ming Hsiung
Affiliation:
[email protected], Lawrence Livermore National Laboratory, Chemistry and Materials Science, 7000 East Avenue, P.O. Box 808, L-352, Livermore, California, 94551, United States, 925-424-3125, 925-424-3815
Jikou Zhou
Affiliation:
[email protected], Lawrence Livermore National Laboratory, Chemistry and Materials Science, United States
Get access

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 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 α phase and Nb-enriched U3Nb 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.

Keywords

phase transformationcrystallographic structuretransmission electron microscopy (TEM)
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 893: Symposium JJ – Actinides 2005 – Basic Science, Applications and Technology , 2005 , 0893-JJ04-08
Copyright
Copyright © Materials Research Society 2006

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

1. Vandermeer, R.A., Acta Metall., 28 (1980), p. 383.10.1016/0001-6160(80)90173-XGoogle Scholar
2. Eckelmeyer, K.H., Romig, A.D., and Weirick, L.J., Met. Trans. A, 15A (1984), p. 1319.10.1007/BF02648560Google Scholar
3. Vandermeer, R.A., Ogle, J.C., and Northcutt, W.G. Jr, Met. Trans. A, 12A (1981), p. 733.10.1007/BF02648337Google Scholar
4. Field, R.D., Thoma, D.J., Dunn, P.S., Brown, D.W., Cady., C.M, Phil. Mag. A, 81 (2001), p. 1691.10.1080/01418610010010971Google Scholar
5. Jackson, R.J., Miley, D. V., Trans. ASM, 61 (1968), p. 336.Google Scholar
6. Beverini, G., Edmonds, D.V., Colloque De Physique, Colloque C8, C8–429.Google Scholar
7. Cahn, J.W., Trans. TMS of AIME, 242 (1968), p. 166.Google Scholar
8. Sato, K. and Stobbs, W.M., Phil. Mag. A, 69 (1994), 349.10.1080/01418619408244349Google Scholar
9. Butler, E.P. and Thomas, G., Acta Metall., 18 (1970), 347.Google Scholar
10. Edington, J.W., Practical Electron Microscopy in Materials Science, Van Nostrand Reinhold, New York, 1976.Google Scholar