Competitive Precipitation and Recrystallization in U-7.5Nb-2.5Zr Alloy

Abstract:

Abstract. Metallic nuclear fuel plates are nowadays an alternative to the ceramic ones in the sense that the uranium density can be increased at lower enrichment. Higher thermal conductivity is also a key factor favouring such fuels for power reactors. Uranium reacts promptly with oxygen and nitrogen at high temperatures to catastrophic corrosion due to non-protective oxide layers, which imparts hot forming processes. The gamma phase body centred cubic structure can be retained at room temperature by annealing the U-7.5Nb-2.5Zr (wt.%) alloy followed by quenching, where the deformation can be extensive. The resulted highly deformed gamma supersaturated structure is subjected further to competitive recovery/recrystallization and phase precipitation phenomena whose are studied in the work. The U-7.5Nb-2.5Zr alloy was melted into plasma and induction furnaces and afterwards annealed to gamma phase. The normalized alloy was cold rolled and underwent isochronal and isothermal treatments. The microstructure evolution was monitored by optical microscopy, X-ray diffraction analysis and hardness measurements. The results show the precipitation events of α” and α+γ₃ phases are dominant over recovery in the range 200oC < T < 500oC. Above 500oC the recrystallization is the main process leading to softening and initial Vickers hardness recovery. One refined gamma phase grain structure was obtained (~8.0 μm) after annealing at 700oC for 2.5 hours.

• Periodical: Defect and Diffusion Forum (Volume 354)
• Pages: 85-91
• DOI: https://doi.org/10.4028/www.scientific.net/DDF.354.85
• Online since: June 2014
• Authors: Denise A. Lopes*, Thomaz Augusto Guisard Restivo, Angelo Fernando Padilha
• Keywords: Cold Rolling, Phase Transformation, Precipitation, U-Nb-Zr Alloy

References

[1] R.W. Cahn, P. Haaswn, E.J. Kramer, B. Frost. In: Materials science and technology - a comprehensice treatment. VCH Verlagsgesellshaft GmBH, Weinheim, v. 10A, (1994).

[2] E.E. Hayes. Recrystallization of Cold-Rolled Uranium, in USAEC Report TDI-2501 (Del.), Massachusetts Intitute of Technology, pp.217-236 (1949).

[3] P.E. Madsen, The Recystalizattion of Rolled Uranium Sheet, Report AERE-M/R-1721, Gt. Brit. Atomic Energy Research Establisiment (1955).

[4] M. Englander. Contribution to the Study of Recristallization o Uranium in the Alpha-Phase: Rev. mét. Vol. 51 (1954) p.758.

[5] G. Ya. Sergeev, V.V. Timova, L.I. Kolobneva. Recrystallization of Cold-Rolled uranium: Journal of Nuclear Energy Part A/B Vol. 17 (1960) pp.444-447.

DOI: 10.1016/0368-3230(63)90109-5

[6] J.L. Snelgrove, G.L. Hofman, M.K. Meyer, C.L. Trybus, T.C. Wiencek. Development of very-high-density low-enriched-uranium fuels: Nucl. Eng. Des. Vol. 178 (1997) p.119–126.

DOI: 10.1016/s0029-5493(97)00217-3

[7] W.D. Wilkinson, Uranium metallurgy Vol. I. Interscience Publishers, 1st edition, New York, USA, pp.02-217 (1962).

[8] A.E. Dwight, M.H., Mueller. Constitution of the uranium-rich U-Nb and U-Nb-Zr systems. ANL-5581, Illinois (1956).

DOI: 10.2172/4317513

[9] W. Lehmann, R.F. Hills. Proposed nomeclature for phase in uranium alloys: Journal Nuclear Material, Vol. 2 (1960) pp.261-268.

[10] X.J. Liu, Z.S. Li, J. Wang, C.P. Wang. Thermodynamic modeling of the U–Mn and U–Nb systems. Journal of Nuclear Materials Vol. 380 , p.99–104, 2008.

DOI: 10.1016/j.jnucmat.2008.07.008

[11] Z.S. Li, X.J. Liu, C.P. Wang, Thermodynamic modeling of the Th–U, Th–Zr and Th–U–Zr systems, v. 476, p.193–198, 2009.

DOI: 10.1016/j.jallcom.2008.09.051

[12] ASM Handbook Volume 3: Alloy Phase Diagrams. Seção 2, p.307, 308 e 381, Ohio, USA (1992).

[13] W.D. Wilkinson, Uranium metallurgy Vol. II. Interscience Publishers, 1st edition, New York, USA, pp.867-1261 (1962).

[14] K.H. Eckelmeyer, In: Uranium and uranium alloys. Metals Handbook, volume 2. 10th ed. Ohio, USA, ASM International (1990).

[15] A.M. Kelly, R.D. Field, D.J. Thoma. Metallographic preparation techniques for U-6 wt. %Nb: J. Nucl. Mat. Vol. 429 (2012) p.118–127.

[16] D.A. Capenter, R.A. Vandermmer. An X-ray diffraction study of a martensitic transformation in uranium alloys: Journal de Physique. Vol. 43 (1982) pp.395-400.

[17] R. K. Ray, J.J. Jonas. Transformation textures in steels: Int. Mat. Rev. Vol. 35 (1990) pp.1-36.