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Title: Recovery and Recrystallization Behavior of Nb-Containing Fe-Cr-Al Alloys

Abstract

Nuclear-grade wrought Fe-Cr-Al alloys are currently under development as promising accident-tolerant fuel cladding materials for light water reactors (LWRs) due to their superior oxidation and corrosion resistance in high temperature steam environments when compared with current commercial Zr-based alloys. Sufficient amounts of Cr and Al additions in Fe-Cr-Al alloys provide the improved surface protection effects at both the service temperature and elevated temperatures in the accident case scenario. Minor alloying additions (such as Nb in the current study) also promote the second-phase precipitates to strengthen the alloys; e.g. sub-micron size Fe{sub 2}Nb-type Laves phase precipitates are likely to disperse at both inter- and trans-granular in BCC-Fe matrix after applying proper heat treatments. In LWRs, a seamless tube product is required for the fuel cladding which typically has ∼ 4 m length with an outside diameter of ∼ 10 mm and a wall thickness of less than 0.5 mm, and it imposes considerable challenges for tube fabrication process (e.g. tube drawing) of Fe-Cr-Al alloys. Research has been performed to achieve a balance between high-temperature performance and tube fabricability in newly developed Fe-Cr-Al alloys. BCC-Fe materials with Cr and Al additions typically suffer from poor ductility because of relatively high ductile-brittle transitionmore » temperature. In this sense, the microstructural stability of refined grain or subgrain structure, even at high temperature, is critical to maintain the deformability of the alloys during tube fabrication process, as well as sufficient mechanical properties at service condition. In this study, the recovery and recrystallization behaviors of Nb-containing Fe-Cr-Al alloys are studied. A specific focus was to evaluate the stability of the subgrain structure of the deformed Fe-Cr-Al alloys, and seek optimized processing parameters for seamless tube fabrication. The present results clearly demonstrated that the Nb addition stabilizes the refined subgrain microstructures of Fe-Cr-Al alloys below 700 deg. C due to Laves phase precipitations along sub-boundaries when compared with the Nb-free alloys, while maintaining sufficient strengths needed for fuel cladding in LWRs. At the same time, the results also showed that Nb-containing alloys can be softened through suitable annealing to improve the processability of tube drawing process. Detailed characterization efforts of subgrains and Laves phase precipitates are currently in progress. Completion of this work will deepen the understanding of the recovery and recrystallized behavior of Nb-containing Fe-Cr-Al alloys and provide guidelines to tube drawing process in the alloys. (authors)« less

Authors:
;  [1]
  1. Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States)
Publication Date:
OSTI Identifier:
22992081
Resource Type:
Journal Article
Journal Name:
Transactions of the American Nuclear Society
Additional Journal Information:
Journal Volume: 114; Journal Issue: 1; Conference: Annual Meeting of the American Nuclear Society. Embedded topical meeting 'Nuclear fuels and structural material for the next generation nuclear reactors', New Orleans, LA (United States), 12-16 Jun 2016; Other Information: Country of input: France; 6 refs.; Available from American Nuclear Society - ANS, 555 North Kensington Avenue, La Grange Park, IL 60526 United States; Journal ID: ISSN 0003-018X
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 42 ENGINEERING; ACCIDENT-TOLERANT NUCLEAR FUELS; ALLOYS; ANNEALING; BCC LATTICES; CLADDING; CORROSION RESISTANCE; DUCTILE-BRITTLE TRANSITIONS; DUCTILITY; MATERIALS RECOVERY; MICROSTRUCTURE; OXIDATION; PRECIPITATION; RECRYSTALLIZATION; SAFETY; WATER COOLED REACTORS; WATER MODERATED REACTORS

Citation Formats

Sun, Zhiqian, and Yamamoto, Yukinori. Recovery and Recrystallization Behavior of Nb-Containing Fe-Cr-Al Alloys. United States: N. p., 2016. Web.
Sun, Zhiqian, & Yamamoto, Yukinori. Recovery and Recrystallization Behavior of Nb-Containing Fe-Cr-Al Alloys. United States.
Sun, Zhiqian, and Yamamoto, Yukinori. 2016. "Recovery and Recrystallization Behavior of Nb-Containing Fe-Cr-Al Alloys". United States.
@article{osti_22992081,
title = {Recovery and Recrystallization Behavior of Nb-Containing Fe-Cr-Al Alloys},
author = {Sun, Zhiqian and Yamamoto, Yukinori},
abstractNote = {Nuclear-grade wrought Fe-Cr-Al alloys are currently under development as promising accident-tolerant fuel cladding materials for light water reactors (LWRs) due to their superior oxidation and corrosion resistance in high temperature steam environments when compared with current commercial Zr-based alloys. Sufficient amounts of Cr and Al additions in Fe-Cr-Al alloys provide the improved surface protection effects at both the service temperature and elevated temperatures in the accident case scenario. Minor alloying additions (such as Nb in the current study) also promote the second-phase precipitates to strengthen the alloys; e.g. sub-micron size Fe{sub 2}Nb-type Laves phase precipitates are likely to disperse at both inter- and trans-granular in BCC-Fe matrix after applying proper heat treatments. In LWRs, a seamless tube product is required for the fuel cladding which typically has ∼ 4 m length with an outside diameter of ∼ 10 mm and a wall thickness of less than 0.5 mm, and it imposes considerable challenges for tube fabrication process (e.g. tube drawing) of Fe-Cr-Al alloys. Research has been performed to achieve a balance between high-temperature performance and tube fabricability in newly developed Fe-Cr-Al alloys. BCC-Fe materials with Cr and Al additions typically suffer from poor ductility because of relatively high ductile-brittle transition temperature. In this sense, the microstructural stability of refined grain or subgrain structure, even at high temperature, is critical to maintain the deformability of the alloys during tube fabrication process, as well as sufficient mechanical properties at service condition. In this study, the recovery and recrystallization behaviors of Nb-containing Fe-Cr-Al alloys are studied. A specific focus was to evaluate the stability of the subgrain structure of the deformed Fe-Cr-Al alloys, and seek optimized processing parameters for seamless tube fabrication. The present results clearly demonstrated that the Nb addition stabilizes the refined subgrain microstructures of Fe-Cr-Al alloys below 700 deg. C due to Laves phase precipitations along sub-boundaries when compared with the Nb-free alloys, while maintaining sufficient strengths needed for fuel cladding in LWRs. At the same time, the results also showed that Nb-containing alloys can be softened through suitable annealing to improve the processability of tube drawing process. Detailed characterization efforts of subgrains and Laves phase precipitates are currently in progress. Completion of this work will deepen the understanding of the recovery and recrystallized behavior of Nb-containing Fe-Cr-Al alloys and provide guidelines to tube drawing process in the alloys. (authors)},
doi = {},
url = {https://www.osti.gov/biblio/22992081}, journal = {Transactions of the American Nuclear Society},
issn = {0003-018X},
number = 1,
volume = 114,
place = {United States},
year = {2016},
month = {6}
}