Solidification of Pb-Sn Alloys

Teri MosherUniversity 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

• Solidify in a branched style

40 wt% Sn at 5·10-5m/s

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

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

Procedure

• 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

Hot

Zone

Cold Zone

Quartz Tube

Pb-Sn Alloy

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

Procedure

• Mount each sample both horizontally and vertically

• Polish in order to analyze the microstructure

• Optical Microscopy

Results: 10 wt% Sn

Velocity = 10-4m/s Velocity = 10-5m/s

200 m

Results: 25 wt% Sn

Velocity = 10-4m/s Velocity = 10-5m/s

100 m

Results: 40 wt% Sn

Velocity = 10-4m/s Velocity = 10-5m/s

100 m

Results: 63 wt% Sn

Velocity = 10-4m/s Velocity = 10-5m/s

50 m

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

Scheil Equation

Cα - Ce Fs = 1- (Co/Ce)11-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

ResultsFraction Primary VS Composition

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

0 10 20 30 40 50 60 70

Composition wt% Sn

Fra

cti

on

Pri

mary

Ph

ase

Fast

Medium

Slow

Scheil

Lever

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