Phase Stability in the Fe-Rich Fe-Cr-Ni-Zr Alloys
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I.
INTRODUCTION
RECENT development of Laves phase strengthened Fe-Cr-Ni-Zr ferritic alloys has shown promising applications as new cladding materials of nuclear reactors because of the enhanced high-temperature strength and resistance to creep and radiation hardening, compared to traditional P91 ferritic–martensitic steels.[1,2] Preliminary ion irradiation studies showed that intermetallic phases presented in these alloys such as the Laves Fe2Zr and Fe23Zr6 have different microstructural responses to irradiation.[3] Therefore, it is of interest to establish a baseline of phase stability in these Fe-rich Fe-Cr-Ni-Zr ferritic alloys before irradiation, which, in combination with the studies of irradiation behaviors of different phases, can be used to tailor the microstructure of Fe-Cr-Ni-Zr alloys for nuclear reactor applications.
TIANYI CHEN, YING YANG, and LIZHEN TAN are with the Oak Ridge National Laboratory, P. O. Box 2008 MS6115, Oak Ridge, TN 37831-6115. Contact e-mail: [email protected] This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-publicaccess-plan). Manuscript submitted February 15, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Previous studies in literature on phase stability in the Fe-Cr-Ni-Zr quaternary system have been focused on alloys made from type 304 and 316 stainless steels (SS) and Zr.[4–9] These studies are of interest for understanding the long-term stability of metal waste which is predominantly a mixture of ZIRCALOYS and Fe-CrNi-based SS.[4–10] While many literature results were focused on the Zr-rich region,[4,7,8,10] the studies on the Fe-rich region and Fe2Zr Laves phase[4–6,8] are more relevant to this study and will be compared with the findings from this work. In this study, we alloyed with high-purity Fe, Cr, Ni, and Zr metals to minimize the influence from impurities. The stabilities of intermetallic phases in Fe-rich Fe-CrNi-Zr quaternary system were investigated. The results of this study will be useful to the improvement of relevant thermodynamic models and the development of Zr-containing ferritic alloys.
II.
MATERIAL AND METHODS
Table I lists the chemical compositions of the four alloys, referred to as Z3N3, Z3N7, Z6N5, and Z6N9 in this paper. The starting materials were elemental Fe, Cr, Zr, and Ni in bulk form with purity levels of >99.904, >99.978, >99.2, and >99.15 pct, respectively. Arc melting was used to prepare the alloys in this study as discussed in Reference 1. Buttons with a m
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