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Title: Aging Effects on Microstructural and Mechanical Properties of Select Refractory Metal Alloys for Space Reactor Applications

Abstract

Refractory alloys based on niobium, tantalum and molybdenum are potential candidate materials for structural applications in proposed space nuclear reactors. Long-term microstructural stability is a requirement of these materials for their use in this type of creep dominated application. Early work on refractory metal alloys has shown aging embrittlement occurring for some niobium and tantalum-base alloys at temperatures near 40% of their melting temperatures in either the base metal or in weldments. Other work has suggested microstructural instabilities during long-term creep testing leading to decreased creep performance. This paper examines the effect of aging 1,100 hours at 1098, 1248 and 1398 K on the microstructural and mechanical properties of two niobium (Nb-1Zr and FS-85), tantalum (T-111 and ASTAR-811C) and molybdenum (Mo-41Re and Mo-47.5Re) base alloys. Changes in material properties are examined through mechanical tensile testing coupled with electrical resistivity changes and microstructural examination through optical and electron microscopy analysis.

Authors:
 [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Shared Research Equipment Collaborative Research Center
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
931633
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Nuclear Materials; Journal Volume: 366; Journal Issue: 1-2
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AGING; ALLOYS; ASTAR 811C; CREEP; ELECTRIC CONDUCTIVITY; ELECTRON MICROSCOPY; HEAT RESISTING ALLOYS; MECHANICAL PROPERTIES; NIOBIUM; REACTORS; REFRACTORY METALS; TANTALUM; NESDPS Office of Nuclear Energy Space and Defense Power Systems

Citation Formats

Leonard, Keith J, Busby, Jeremy T, and Zinkle, Steven J. Aging Effects on Microstructural and Mechanical Properties of Select Refractory Metal Alloys for Space Reactor Applications. United States: N. p., 2007. Web. doi:10.1016/j.jnucmat.2007.03.025.
Leonard, Keith J, Busby, Jeremy T, & Zinkle, Steven J. Aging Effects on Microstructural and Mechanical Properties of Select Refractory Metal Alloys for Space Reactor Applications. United States. doi:10.1016/j.jnucmat.2007.03.025.
Leonard, Keith J, Busby, Jeremy T, and Zinkle, Steven J. Mon . "Aging Effects on Microstructural and Mechanical Properties of Select Refractory Metal Alloys for Space Reactor Applications". United States. doi:10.1016/j.jnucmat.2007.03.025.
@article{osti_931633,
title = {Aging Effects on Microstructural and Mechanical Properties of Select Refractory Metal Alloys for Space Reactor Applications},
author = {Leonard, Keith J and Busby, Jeremy T and Zinkle, Steven J},
abstractNote = {Refractory alloys based on niobium, tantalum and molybdenum are potential candidate materials for structural applications in proposed space nuclear reactors. Long-term microstructural stability is a requirement of these materials for their use in this type of creep dominated application. Early work on refractory metal alloys has shown aging embrittlement occurring for some niobium and tantalum-base alloys at temperatures near 40% of their melting temperatures in either the base metal or in weldments. Other work has suggested microstructural instabilities during long-term creep testing leading to decreased creep performance. This paper examines the effect of aging 1,100 hours at 1098, 1248 and 1398 K on the microstructural and mechanical properties of two niobium (Nb-1Zr and FS-85), tantalum (T-111 and ASTAR-811C) and molybdenum (Mo-41Re and Mo-47.5Re) base alloys. Changes in material properties are examined through mechanical tensile testing coupled with electrical resistivity changes and microstructural examination through optical and electron microscopy analysis.},
doi = {10.1016/j.jnucmat.2007.03.025},
journal = {Journal of Nuclear Materials},
number = 1-2,
volume = 366,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • This work is concerned with the effects of added boron (0.1 w/o) on mechanical properties and martensitic transformation temperatures (Ms) of the Cu - 14.0 Zn - 8.5. Al shape memory alloy. The composition was designed to have Ms temperature in the vicinity of 100/sup 0/C. The influence of applying step quenching on the variation in Ms temperatures has been studied in boron-free Cu - 14.0 Zn - 8.5 Al and boron-containing Cu - 14.0 Zn 8.5 Al - 0.1 B alloys. Aging kinetics and transformation temperatures have been determined by electrical resistivity measurements.
  • The proposed use 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, the lead 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, a relatively small database exists for the properties of FS-85. These gaps include potential microstructural instabilities that can lead to mechanical property degradation. In this work, changes in microstructure and mechanicalmore » properties of FS-85 were investigated following 1100 h 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, scanning and transmission electron microscopy. 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 1248 K aged material, while ductile behavior occurred in material aged above and below this temperature. The effect of temperature on the under and overaging of the grain boundary particles are believed to have contributed to the mechanical property behavior of the aged material.« less
  • Several Mo- and Ta-base alloys have been selected as candidate materials for space reactor heat transfer applications. The initial phase of this investigation has compared the effects of inert and oxidizing atmospheres on tensile and bend properties of these alloys. Microstructural variables include texture and degree of recrystallization. Results are discussed with implications for future elevated temperature testing.
  • The changes in microstructure and mechanical properties of Mo-41Re and Mo-47.5Re alloys were investigated following 1100 h aging at 1098, 1248 and 1398 K. The electrical resistivity, hardness and tensile properties of the alloys were measured both before and after aging, along with the alloy microstructures though investigation by optical and electron microscopy techniques. The Mo-41Re alloy retained a single phase solid solution microstructure following 1100 h aging at all temperatures, exhibiting no signs of precipitation, despite measurable changes in resistivity and hardness in the 1098 K aged material. Annealing Mo-47.5Re for 1 h at 1773 K resulted in amore » two-phase (alpha)Mo + sigma structure, with subsequent aging at 1398 K producing a further precipitation of the sigma nphase along the grain boundaries. This resulted in increases in resistivity, hardness and tensile strength with a corresponding reduction in ductility. Aging Mo-47.5Re at 1098 and 1248 K led to the development of the chi-phase along grain boundaries, resulting in decreased resistivity and increased hardness and tensile strength while showing no loss in ductility relative to the as-annealed material.« less