Low temperature age hardening in U–13 at.% Nb: An assessment of chemical redistribution mechanisms

• Published in: Journal of nuclear materials Vol. 393; no. 2; pp. 282 - 291
• Main Authors: Clarke, A.J., Field, R.D., Hackenberg, R.E., Thoma, D.J., Brown, D.W., Teter, D.F., Miller, M.K., Russell, K.F., Edmonds, D.V., Beverini, G.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-09-2009; Elsevier
• Subjects: Applied sciences; Controled nuclear fusion plants; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Fuels; Installations for energy generation and conversion: thermal and electrical energy; Nuclear fuels; Hardening; Impurity; Ageing; Concentration effect; Mechanical properties; Tomography; Niobium; Strength; Nuclear reactor
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2009.06.025

Low temperature aging (<350
°C) of U–13
at.% Nb martensite results in increased strength levels accompanied by significant ductility loss. To determine the decomposition mechanism(s) responsible for these mechanical property changes, atom probe tomography was used to examine the niobium and impurity distributions after aging at 200 or 300
°C for times ranging from 2
h to 70
days. No patterns of niobium or impurity atoms were observed that would indicate segregation to the martensitic twin interfaces, making this hardening mechanism unlikely. Phase separation into roughly equiaxed regions of high and low niobium concentration was clearly observed after aging at 300
°C for 70
days. However, only subtle niobium concentration changes were observed after aging at 200
°C relative to the as-quenched condition, indicating that conventional phase separation is an unlikely explanation for the dramatic mechanical property changes at 200
°C. Therefore, consideration of aging mechanisms other than segregation and phase separation may be warranted.