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 -5 m/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 Growth Pb-1 Wt% Sn V= 5 · 10 -5 m/s dT/dx = 10 K/mm 3.2 mm by 6.4 mm

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

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

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

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

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

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

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

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 Lever Law fs = C o - C e Scheil Equation C α - C e Fs = 1- (Co/Ce) 1 1-k Equilibrium Diffusion of both solid and liquid are rapid Diffusion of solute does not occur in solid Diffusion of solute in liquid is rapid and complete

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