Sizing up mechanical testing: Comparison of microscale and mesoscale mechanical testing techniques on a FeCrAl welded tu
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Sizing up mechanical testing: Comparison of microscale and mesoscale mechanical testing techniques on a FeCrAl welded tube Jonathan G. Gigax1,a) , Avery J. Torrez2, Quinn McCulloch1, Hyosim Kim2, Stuart A. Maloy2, Nan Li1 1
Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM 87545, USA MST-8, Los Alamos National Laboratory, Los Alamos, NM 87545, USA a) Address all correspondence to this author. e-mail: [email protected] 2
Received: 7 April 2020; accepted: 7 July 2020
FeCrAl alloys are among the best and most mature accident tolerant fuel cladding candidates produced to date, due to their superior combination of mechanical properties and stability at elevated temperatures. For fuel cladding applications, these materials are drawn into tubes with plugs welded to the ends. The mechanical properties of such welds and the impact on cladding performance have not been fully investigated. A novel mesoscale mechanical test and a variety of microscale tests were performed to evaluate a range of properties including nanoindentation hardness, compression and shear yield strengths, and tensile strengths and elongations. Micromechanical testing generally matched the trends of the larger mesoscale testing, with nanoindentation reproducing the trend the best, although some discrepancies existed in regions with low dislocation content. Mesoscale tensile testing showed good correlation with macroscale tests and revealed that the plug heat-affected zone possessed the lowest strength and ductility. This indicated that failure would occur first in or near this region.
INTRODUCTION Among several candidates for “accident tolerant” fuel cladding, FeCrAl alloys are among the top choices due to their superior high temperature oxidation resistance, aqueous corrosion resistance, low radiation-induced swelling, and tolerance to loss-of-coolant accident conditions [1,2,3,4]. Despite their higher neutron absorption cross-section compared with zirconium-based alloys, the mechanical and chemical stability over a range of environments makes this alloy an attractive candidate. Nominally comprised of Fe, Cr, and Al with some minor alloying elements, FeCrAl alloys feature a protective aluminum oxide layer (scale) at high temperatures. Ongoing work at Oak Ridge National Laboratory has focused on an optimized composition of a FeCrAl alloy for tube processing and deployment into light water reactors [5]. Recent testing has resulted in one alloy being down-selected for such use: C26M. This body-centered cubic alloy has a nominal composition of Fe–12Cr–6Al with grain sizes ranging from 10 to 100 μm, depending on heat treatments used. Additional information
© Materials Research Society 2020
on the processing steps and properties of FeCrAl alloys can be found in Refs [2,6]. As part of a fuel assembly, FeCrAl tubes are typically welded to a plug which is used to seal the cladding tube and fix its position within a fuel bundle. For this particular alloy, tungsten inert gas (TIG) welding was chosen due to its extensive his
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