ME328 Materials Engineering
Homework 3
The article this week “Calculation of Phase Equilibria in Candidate Solder Alloys” is likely to have sections
beyond the understanding of most undergraduate MEs unless they have a strong interest in equilibrium
thermodynamics, chemistry or metallurgy.
(Double click to read the article)
The most important parts that will be within your understanding are highlighted in yellow with key
words boxed in red.
1. Why are we concerned with replacing Pb in solder?
2. What are the important design characteristics of current 60-40 or 50-50 Pb-Sn solder that we would like
to maintain in future solders?
3. Define the following key words that show up in the article
a) Eutectic reaction
b) Liquidus temperature
c) Solidus temperature
d) Lever Rule
4. What is the difference between a Binary and a Ternary Equilibrium Phase Diagram.
5. The following link takes you the NIST site that shows Binary and Ternary Phase Diagrams for a number
of combinations of elements. Please consider the Pb-Sn, Bi-Sn and Ag-Cu Systems
http://www.metallurgy.nist.gov/phase/solder/solder.html
For each System, name the Eutectic temperature, the Eutectic Composition, and the melting range of a
50-50 alloy.
System
Pb-Sn
Bi-Sn
Ag-Cu
Eutectic Temp
Eutectic Comp
(% of each alloy)
Melting Range
(temperature)
6. Use the Ag-Cu diagram to answer the following
a) name the temperature that a 70%Ag-30%Cu alloy will be fully liquid
Name the phase(s) present, the chemical compositions of each phase and the relative amounts of each
phase for a 70%Ag-30%Cu alloy at
b) 1100C
c) 825C
d) 200C
9. Go to http://www-g.eng.cam.ac.uk/mmg/teaching/ and select Iron-Carbon Phase Diagram from the
Teach Yourself Phase Diagrams section. Go through the example to see how the eutectoid
microstructure and the hypoeutectoid forms.
a) name the eutectoid microstructure for iron carbon
b) state the difference between eutectic and eutectoid
c) What phases are present in the eutectoid microstructure
d) What carbon composition would a hypo-eutectoid microstructure have?
e) For a eutectoid composition steel alloy, name the phase(s) present at 800C.
f) Describe the microstructure of a 1020 steel at room temperature in terms of the phases and micro
constituents present (a sketch may be helpful).
(extra fun but not extra credit) If you want to know more about how a phase diagram can be determined
experimentally, the following web site is good. Note that the authors have focused this on 16-18 year
olds.
http://www.chemguide.co.uk/physical/phaseeqia/snpb.html