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Type |
Krug, Matthew E.; Dunand, David C.; Seidman, David N. |
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Publication |
Effects of Li additions on precipitation-strengthened Al-Sc and Al-Sc-Yb alloys |
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Journal Article |
Pages |
2011 |
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Abstract |
Acta Materialia |
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59 |
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Summary Language |
1700-1715 |
Series Editor |
aluminium alloys, atom-probe field-ion microscopy (AP-FIM), rare earth, nanostructure, precipitation; Al-Sc |
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Abbreviated Series Title |
Two Al-Sc based alloys (Al-0.12 Sc and Al-0.042 Sc-0.009 Yb, at. %) and their counterparts with
Li-additions (Al-2.9 Li-0.11 Sc and Al-5.53 Li-0.048 Sc-0.009 Yb, at. %) are aged at 325 °C. For
both base alloys, the addition of Li results in greater peak hardness from incorporation of Li in the
L12-structured alpha'–Al3(Sc,Li) and alpha'–Al3(Sc,Li,Yb) precipitates, and a concomitant increase in
number density and volume fraction of the precipitates and a reduction in their mean radius. These
changes result from a combination of (i) an increase in the driving force for precipitate nucleation
due to Li, (ii) a decrease in the elastic energy of the coherent misfitting precipitates from a decrease
in their lattice parameter mismatch due to their Li content, and (iii) a decrease in the interfacial free
energy, as determined from measurements of relative Gibbsian interfacial excess of Li. In Al-2.9 Li-
0.11 Sc (at. %), the Li content of the precipitates drops from 9.1 at. % in the peak-aged state (8 h) to
5.7 at. % in the overaged state (1536 h). As a result, the precipitate volume fraction decreases from
0.56% at peak-age to 0.45% at 1536 h. In Al-5.53 Li-0.048 Sc-0.009 Yb (at. %), the relatively
limited Li concentration produces only a small increase in Vickers microhardness from precipitation
of metastable delta'–Al3Li upon a second aging at 170 °C following the primary aging at 325 °C. |
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NU @ karnesky @ |
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10984 |
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