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On the Diffusivity of Au in Pb

Published online by Cambridge University Press:  26 February 2011

Ann N. Campbell  and
David Turnbull
Ann N. Campbell
Affiliation:
Division of Applied Sciences, Harvard University Cambridge, MA 02138
David Turnbull
Affiliation:
Division of Applied Sciences, Harvard University Cambridge, MA 02138
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Abstract

The precipitation of Pb3Au from dilute Pb(Au) alloys and the subsequent Ostwald ripening of the precipitate phase have been studied. The Au diffusivity which limits the precipitation from Pb(500 at. ppm Au) specimens is in good agreement with Dp = 45 exp[(−20.8 kcal/mol)/RT], found previously to control the precipitation rate in Pb(900–1000 at. ppm Au) alloys (Rossolimo and Turnbull, 1973). In contrast, precipitation from Pb(100 at. ppm Au) alloys and Ostwald ripening in the Pb(500 at. ppm Au) specimens appear to be governed by the high temperature Au tracer diffusivity, DAu = 0.0041 exp[(−9.35 kcal/mol)/RT], which is about 103 times greater than Dp at the temperatures of interest, 75 to 112°C, and is attributed to the motion of a Au interstitial defect. In the 100 ppm alloys the Au is incorporated most easily at the ends of the Pb3Au crystals and a ribbon- or whisker-like morphology results. The particles which form at the grain boundaries in the 500 ppm Au alloy specimens are at least six times larger in volume than the matrix particles and ripen at their expense. The Ostwald ripening kinetics of the grain boundary particles scale with t1/2 rather than with t1/3 as is usual. The Pb3Au formed whiskers, blades, ribbons, or equiaxed particles depending upon the Au concentration and precipitation temperature. The precipitation and ripening kinetics are critically dependent on the morphology of the second phase.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 57: Symposium I – Phase Transitions in Condensed Systems--Experiments and Theory , 1985 , 369
Copyright
Copyright © Materials Research Society 1987

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