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Type Knipling, Keith E.; Dunand, David C.; Seidman, David N.
  Publication Nucleation and Precipitation Strengthening in Dilute Al-Ti and Al-Zr Alloys Volume Journal Article
Pages 2007
  Abstract Metallurgical and Materials Transactions A  
  Corporate Author  
Publisher 38  
Editor 10
  Summary Language 2552-2563 Series Editor Al-Zr; Al-Ti  
Abbreviated Series Title Two conventionally solidified Al-0.2Ti alloys (with 0.18 and 0.22 at. pct Ti) exhibit no hardening after aging up to 3200 hours at 375 C or 425 C. This is due to the absence of Al3Ti precipitation, as confirmed by electron microscopy and electrical conductivity measurements. By contrast, an Al-0.2Zr alloy (with 0.19 at. pct Zr) displays strong age hardening at both temperatures due to precipitation of Al3Zr (L12) within Zr-enriched dendritic regions. This discrepancy between the two alloys is explained within the context of the equilibrium phase diagrams: (1) the disparity in solid and liquid solubilities of Ti in alpha-Al is much greater than that of Zr in alpha-Al; and (2) the relatively small liquid solubility of Ti in alpha-Al limits the amount of solute retained in solid solution during solidification, while the comparatively high solid solubility reduces the supersaturation effecting precipitation during post-solidification aging. The lattice parameter mismatch of Al3Ti (L12) with alpha-Al is also larger than that of Al3Zr (L12), further hindering nucleation of Al3Ti. Classical nucleation theory indicates that the minimum solute supersaturation required to overcome the elastic strain energy of Al3Ti nuclei cannot be obtained during conventional solidification of Al-Ti alloys (unlike for Al-Zr alloys), thus explaining the absence of Al3Ti precipitation and the presence of Al3Zr precipitation.
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no NU @ karnesky @ 1908
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