Metallurgical and Materials Transactions A

, Volume 40, Issue 4, pp 838–855 | Cite as

Nb-Base FS-85 Alloy as a Candidate Structural Material for Space Reactor Applications: Effects of Thermal Aging

  • Keith J. LeonardEmail author
  • Jeremy T. Busby
  • David T. Hoelzer
  • Steven J. Zinkle


The proposed uses of fission reactors for manned or deep space missions have typically relied on the potential use of refractory metal alloys as structural materials. Throughout the history of these programs, a leading candidate has been Nb-1Zr, due to its good fabrication and welding characteristics. However, the less-than-optimal creep resistance of this alloy has encouraged interest in the more complex FS-85 (Nb-28Ta-10W-1Zr) alloy. Despite this interest, only a relatively small database exists for the properties of FS-85. Database gaps include the potential microstructural instabilities that can lead to mechanical property degradation. In this work, changes in the microstructure and mechanical properties of FS-85 were investigated following 1100 hours of thermal aging at 1098, 1248, and 1398 K. The changes in electrical resistivity, hardness, and tensile properties between the as-annealed and aged materials are compared. Evaluation of the microstructural changes was performed through optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The development of intragranular and grain-boundary precipitation of Zr-rich compounds as a function of aging temperature was followed. Brittle tensile behavior was measured in the material aged at 1248 K, while ductile behavior occurred in samples aged above and below this temperature. The effect of temperature on the under- and overaging of the grain-boundary particles is believed to have contributed to the mechanical property behavior of the aged materials.


Electrical Resistivity Electrical Discharge Machine Aging Temperature Thermal Aging Dynamic Strain Aging 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



The authors express their gratitude to J. Hack, R. Baranwal, T.M. Angeliu, and Y. Ballout of the Naval Reactors Prime Contractor Team, for many helpful technical discussions and for their guidance. The authors also thank Marie Williams, Mike Pershing, and Cliff Davison, for their help in the acid cleaning and annealing of the specimens prior to thermal aging; Jeffrey McNabb and Bob Sitterson, for welding and leak testing the alloy 600 aging cans; Brian Sparks and David Harper, for thermal aging the encapsulated materials; and Kathy Thomas and Jackie Mayotte, for their help in preparing samples for microscopy. The authors also thank Louis K. Mansur and Chad E. Duty for their helpful discussions and their review of this article. This work was performed under the sponsorship of the NASA Project Prometheus and was directed by the U.S. Department of Energy/National Nuclear Security Administration (DOE/NNSA) Naval Reactors. Opinions and conclusions drawn by the authors are not endorsed by the DOE/NNSA Naval Reactors. Research at the Oak Ridge National Laboratory (ORNL) SHaRE User Center was sponsored by the Division of Materials Sciences and Engineering, DOE. The ORNL is managed for the DOE by UT-Battelle, LLC, under Contract No. DE-AC-05-00OR22725.


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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2009

Authors and Affiliations

  • Keith J. Leonard
    • 1
    Email author
  • Jeremy T. Busby
    • 1
  • David T. Hoelzer
    • 1
  • Steven J. Zinkle
    • 1
  1. 1.Oak Ridge National LaboratoryMaterials Science and Technology DivisionOak RidgeUSA

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