1.
3. (10 marks). Based on Chapter 2. With reference to the Cu-Ag eutectic phase diagram below,
answer the following questions. Express all compositions in weight percent Ag, e g a Cu alloy
containing 10 weight percent of Ag is written as Cu-10 w1% Ag Don'use the top
horizontalaisonthird? gram. First, label all parts of the phase diagram with Greek characters,?, ?,
etc. Composition (at% Ag) 100 1200 1000 800 790C 1.9 91.2 1200 600 1000 400 200 100
Composition (wt% Ag) (a) What is the chemical composition of the very first solid to appear in a
liquid alloy of average composition Cu-20 wt% Ag that is cooled slowly from 1 100°C?
Answer: (b) At what temperature does this solid begin to form? Answer: (c) For this alloy (i)
What are the compositions (in wt %) of the two phases that are present at 900°C? Answers: (il)
What are the relative fractions/amounts of these two phases that are present at 900°C? Answers
(d) For this alloy (i) What are the compositions in wt % of the two phases present at 700°C?
Answers: (ii) What are the relative fractions/amounts of the two phases present at 700°C?
Answers: (e) What is the lowest temperature a liquid Cu-Ag alloy can exist at and what is the
composition of that
Solution
(a) 1000 °C since after cooling from 1100 ° C the liquidus curve has 1000 ° C as
temperature for 20% Ag wt compositioon
(b) around 300 °C, as u see the solidus curve begins from around 300 ° C on temperature
axis.
(c) 8 % and 43% respectively, as u can see the intersections of the 900 ° C line with the curve.
(ii) Fraction would be (92% Cu 8%Ag), (57%Cu 43%Ag)
(d) 5% and 93 % repectively, as u can see the intersections of the 700 ° C line with the curve.
(ii) Fraction would be (95% Cu 5%Ag), (7%Cu 93%Ag)
(e) 500 F is the lowest temperature at which the alloy can exist as u can see the curve ends at 500
K mark on the right side which is slightly lower than the initial temperature of 300 ° C .
COmposition - 0% Cu 100%Ag