solidification of pb-sn alloys
DESCRIPTION
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 Solidify in a branched style. - PowerPoint PPT PresentationTRANSCRIPT
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