Solidification of PbSn Alloys Teri Mosher University of

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

Presentation Overview • • Dendrites Purpose Procedure Results

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

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

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

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

2 D Model of Dendrite Growth Pb-1 Wt% Sn V= 5· 10 -5 m/s d. T/dx = 10 K/mm 3. 2 mm by 6. 4 mm

Procedure Pb-Sn Alloy • 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 Quartz Tube Hot Zone Cold Zone

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

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

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

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

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

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

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.

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

Results

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

Acknowledgements • National Science Foundation • Professor Krane • Srinivasan Raghavan