BULK NANOSTRUCTURED STEELS FOR NUCLEAR REACTOR AND EXTREME ENVIRONMENT APPLICATIONS
"Candidate accident tolerant FeCrAl fuel (ATF) claddings for light water reactors (LWRs) need to be thinner than current Zircaloys owing to higher neutronic penalty, demanding an improvement in strength. Therefore, equal channel angular pressing (ECAP), and high-pressure torsion (HPT) were used to produce bulk ultra-fine grained and nanocrystalline Kanthal-D [KD; Fe-21Cr-5Al-0.026C (wt.%) alloy] which resulted in an improvement in strength of up to 3 times their nominal strength from grain boundary strengthening, and dislocation strengthening. Dynamic recovery was promoted due to ECAP at 520 oC rendering it with a large area fraction of less mobile low angle grain boundaries (LAGBs) which thermally stabilized it up to 500 C, well above the operating temperature of an LWR. FeCrAl alloys suffer from embrittlement after long-term aging around 475 C, due to separation of Cr-enriched α’, which is further accelerated in a nuclear environment because of irradiation induced point defects enhancing diffusion. Nanostructured materials have been shown to have better irradiation tolerance owing to the high-volume fraction of GBs acting as effective sinks for irradiation, and thermally induced vacancies. Accordingly, in this study, irradiation and thermally induced α’ precipitation was found to decrease with that of grain size. This study is the first to address this issue from a kinetics perspective as opposed to the existing thermodynamic approach of varying the Cr and Al content to reduce α’ phase separation. This study is also the first to systematically scrutinize the influence of grain size on irradiation and thermally induced α’ precipitation/phase separation in a compositionally homogeneous, and oxide dispersion strengthening (ODS) dispersoid free FeCrAl matrix"--Abstract, p. iv
475C embrittlement, FeCrAl alloy, Ion irradiation, Nanostructured Steels, Severe plastic deformation, Thermal stability, Materials Science and Engineering
Missouri University of Science and Technology
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