Journal
JOURNAL OF MATERIALS SCIENCE
Volume 54, Issue 4, Pages 3485-3495Publisher
SPRINGER
DOI: 10.1007/s10853-018-3036-3
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Funding
- MRI program of the National Science Foundation [DMR-0420532]
- DURIP program of the Office of Naval Research [N00014-0400798, N00014-0610539, N00014-0910781, N00014-1712870]
- National Science Foundation's MRSEC program [NSF DMR-1720139]
- Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource [NSF ECCS-1542205]
- Initiative for Sustainability and Energy at Northwestern (ISEN)
- Braidy Industries
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The age hardening response of Al-0.09Sc (at.%), to which trace amounts (<100ppm) of actinides (An=U or Th) were added, is studied by microhardness, conductivity, transmission electron microscopy, and atom probe tomography (APT). Peak-age hardening at 300 degrees C is associated with a high number density of nanoscale L1(2)-Al-3(Sc(1-x)An(x)) precipitates with core/shell structure. The first alloy Al-0.09Sc-0.006U (at.%) has a peak microhardness similar to that of binary Al-0.09Sc (at.%), but a shorter incubation period for hardening which is consistent with U diffusing faster than Sc in Al and acting as nucleant for Al3Sc. This is confirmed by APT measurements of precipitate composition, Al-3(Sc0.8U0.2), showing that U has high solubility in Al3Sc precipitates and segregates at their core. The second alloy, Al-0.09Sc-0.008Th (at.%), exhibits Th-poor Al-3(Sc0.98Th0.02) precipitates with Th segregation in their shells and it has microhardness evolution undistinguishable from binary Al-0.09Sc; this is indicative of low solubility of Th in L1(2)-Al3Sc and/or low diffusivity of Th in Al. These two primordial actinides -U and Th- show different abilities to coprecipitate with Al3Sc precipitate in aluminum, they, however, both improve coarsening resistance after 143 days at 300 degrees C by forming core/shell structure.
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