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Solidification of Pb-Sn Alloys

Solidification of Pb-Sn Alloys

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Solidification of Pb-Sn Alloys

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  1. Solidification of Pb-Sn Alloys Teri Mosher University of Illinois Advisor: Professor Krane

  2. Presentation Overview • Dendrites • Purpose • Procedure • Results

  3. Dendrites • Primary Phases • First phase to solidify • Solid structures that form from a liquid • Solidify in a branched style 40 wt% Sn at 5·10-5m/s

  4. Dendrites • The shape, size, and speed of dendrite growth influence the final properties of metals. • The morphology of the dendrites determines if the material is: • Soft • Hard • Strong

  5. Pb-Sn Phase Diagram http://cyberbuzz.gatech.edu/asm_tms/phase_diagrams/

  6. Purpose • To observe and analyze the microstructure of Pb-Sn alloys • To compare experimental data to that of a numerical model • Constrained solidification • Velocity • Temperature Gradient

  7. 2D Model of Dendrite GrowthPb-1 Wt% Sn V= 5·10-5m/s dT/dx = 10 K/mm 3.2 mm by 6.4 mm

  8. Procedure Pb-Sn Alloy • Melt samples of the alloy and draw into tube • In the furnace, heat the sample of Pb-Sn up to 400oC with a temperature gradient of 4.5oC/mm Quartz Tube Hot Zone Cold Zone

  9. Procedure • Run the sample through that furnace with four different compositions each at three different velocities • 10wt%, 25wt%, 40wt%, 63wt% • Velocities 10-4m/s, 5·10-5m/s, 10-5m/s

  10. Procedure • Mount each sample both horizontally and vertically • Polish in order to analyze the microstructure • Optical Microscopy

  11. Results: 10 wt% Sn 200 m Velocity = 10-4m/s Velocity = 10-5m/s

  12. Results: 25 wt% Sn 100 m Velocity = 10-4m/s Velocity = 10-5m/s

  13. Results: 40 wt% Sn 100 m Velocity = 10-5m/s Velocity = 10-4m/s

  14. Results: 63 wt% Sn 50 m Velocity = 10-5m/s Velocity = 10-4m/s

  15. Results: Observations • At a slower velocity the dendritic branches are more coarse • The lower the weight percent of tin, the larger the fraction of primary solid.

  16. Lever Law vs Scheil Scheil Equation Lever Law fs = Co - Ce 1 1-k Cα- Ce Fs = 1- (Co/Ce) • Diffusion of solute does not occur in solid • Diffusion of solute in liquid is rapid and complete • Equilibrium • Diffusion of both solid and liquid are rapid

  17. Results

  18. Results: Conclusions • Velocity did not have much effect on the fraction of primary solid. • There was more diffusion occurring at higher compositions

  19. Acknowledgements • National Science Foundation • Professor Krane • Srinivasan Raghavan