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The columnar to equiaxed transition in Pb-Sn and Sn-Pb alloys

University of British Columbia

The columnar to equiaxed transition has been studied experimentally using accurate temperature measurements and with a heat transfer mathematical model in Pb-1.5%Sn and Sn-10%Pb alloys. The behaviour of the two alloys was markedly different. In the Pb-1.5%Sn alloy, the transition did not occur until a large portion of the liquid thermally supercooled. At this point the temperature gradient in the liquid is very low, approximately O℃/mm. For Sn-10%Pb, the transition occurred at a positive temperature gradient of approximately 0.12℃/mm which confirms earlier work by Mahapatra and Weinberg. Supercooling was also found to occur in this alloy but it is not certain whether the supercooling is constitutional or thermal. The difference in the behaviour of the two alloys is related to the density of nuclei prior to directional solidification. Altering the method to release latent heat by using the Scheil equation or the Lever rule instead of the traditional linear assumption in the mathematical model did not have a significant effect on the predicted temperatures or temperature gradients in the Pb-1.5%Sn alloy. The effect was seen when the Sn-10%Pb alloy was considered. The difference is attributed to the total amount of latent heat to be released by a particular alloy.

Text

2010-10-29

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http://hdl.handle.net/2429/29658

Materials Engineering

University of British Columbia

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