Effects of Li additions on precipitation-strengthened Al–Sc and Al–Sc–Yb alloys
| Autor: | David C. Dunand, David N. Seidman, Matthew E. Krug |
|---|---|
| Rok vydání: | 2011 |
| Předmět: |
chemistry.chemical_classification
Materials science Number density Polymers and Plastics Base (chemistry) Precipitation (chemistry) Metallurgy Metals and Alloys Elastic energy Analytical chemistry Nucleation Indentation hardness Electronic Optical and Magnetic Materials Lattice constant chemistry Volume fraction Ceramics and Composites |
| Zdroj: | Acta Materialia. 59:1700-1715 |
| ISSN: | 1359-6454 |
| DOI: | 10.1016/j.actamat.2010.11.037 |
| Popis: | Two Al–Sc-based alloys (Al–0.12Sc and Al–0.042Sc–0.009Yb, at.%) and their counterparts with Li additions (Al–2.9Li–0.11Sc and Al–5.53Li–0.048Sc–0.009Yb, 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 L1 2 -structured α′-Al 3 (Sc,Li) and α′-Al 3 (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 the relative Gibbsian interfacial excess of Li. In Al–2.9Li–0.11Sc (at.%), the Li concentration of the precipitates decreases from 9.1 at.% in the peak-aged state (8 h) to 5.7 at.% in the over-aged state (1536 h). As a result, the precipitate volume fraction decreases from 0.56% at peak aging time to 0.45% at 1536 h. In Al–5.53Li–0.048Sc–0.009Yb (at.%), the relatively limited Li concentration produces only a small increase in Vickers microhardness from precipitation of metastable δ′-Al 3 Li upon a second aging at 170 °C following the primary aging at 325 °C. |
| Databáze: | OpenAIRE |
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