Page 378 - Materials Science and Engineering An Introduction

350 • Chapter 9 / Phase Diagrams

9.8 How many kilograms of nickel must be added to 9.15 A copper–zinc alloy of composition 75 wt% Zn–25
1.75 kg of copper to yield a liquidus temperature wt% Cu is slowly heated from room temperature.
of 1300 C?
(a) At what temperature does the first liquid
9.9 How many kilograms of nickel must be added to phase form?
5.43 kg of copper to yield a solidus temperature of (b) What is the composition of this liquid phase?
1200 C?
(c) At what temperature does complete melting
Interpretation of Phase Diagrams of the alloy occur?
9.10 Cite the phases that are present and the phase (d) What is the composition of the last solid re-
compositions for the following alloys: maining prior to complete melting?
(a) 15 wt% Sn–85 wt% Pb at 100 C (212 F)
9.16 For an alloy of composition 52 wt% Zn–48
(b) 25 wt% Pb–75 wt% Mg at 425 C (800 F) wt% Cu, cite the phases present and their mass
fractions at the following temperatures: 1000 C,
(c) 85 wt% Ag–15 wt% Cu at 800 C (1470 F)
800 C, 500 C, and 300 C.
(d) 55 wt% Zn–45 wt% Cu at 600 C (1110 F)
9.17 Determine the relative amounts (in terms of
(e) 1.25 kg Sn and 14 kg Pb at 200 C (390 F) mass fractions) of the phases for the alloys and
(f) 7.6 lb m Cu and 144.4 lb m Zn at 600 C (1110 F) temperatures given in Problem 9.10.
(g) 21.7 mol Mg and 35.4 mol Pb at 350 C (660 F) 9.18 A 2.0-kg specimen of an 85 wt% Pb–15 wt% Sn
alloy is heated to 200 C (390 F); at this temperature
(h) 4.2 mol Cu and 1.1 mol Ag at 900 C (1650 F)
it is entirely an a-phase solid solution (Figure 9.8).
9.11 Is it possible to have a copper–silver alloy that, at The alloy is to be melted to the extent that 50% of
equilibrium, consists of a b phase of composition the specimen is liquid, the remainder being the a
92 wt% Ag–8 wt% Cu and also a liquid phase of phase. This may be accomplished by heating the
composition 76 wt% Ag–24 wt% Cu? If so, what alloy or changing its composition while holding the
will be the approximate temperature of the alloy? temperature constant.
If this is not possible, explain why.
(a) To what temperature must the specimen be
9.12 Is it possible to have a copper–silver alloy that, heated?
at equilibrium, consists of an a phase of composi-
tion 4 wt% Ag–96 wt% Cu and also a b phase of (b) How much tin must be added to the 2.0-kg
composition 95 wt% Ag–5 wt% Cu? If so, what specimen at 200 C to achieve this state?
will be the approximate temperature of the alloy? 9.19 A magnesium–lead alloy of mass 7.5 kg consists
If this is not possible, explain why. of a solid a phase that has a composition just
9.13 A lead–tin alloy of composition 30 wt% Sn–70 slightly below the solubility limit at 300 C (570 F).
wt% Pb is slowly heated from a temperature of (a) What mass of lead is in the alloy?
150 C (300 F).
(b) If the alloy is heated to 400 C (750 F), how
(a) At what temperature does the first liquid much more lead may be dissolved in the a phase
phase form? without exceeding the solubility limit of this phase?
(b) What is the composition of this liquid phase? 9.20 Consider 2.5 kg of a 80 wt% Cu–20 wt% Ag cop-
(c) At what temperature does complete melting per–silver alloy at 800 C. How much copper must
of the alloy occur? be added to this alloy to cause it to completely
(d) What is the composition of the last solid re- solidify 800 C?
maining prior to complete melting? 9.21 A 65 wt% Ni–35 wt% Cu alloy is heated to a
9.14 A 50 wt% Ni–50 wt% Cu alloy is slowly cooled temperature within the a liquid-phase region.
from 1400 C (2550 F) to 1200 C (2190 F). If the composition of the a phase is 70 wt% Ni,
determine
(a) At what temperature does the first solid
phase form? (a) the temperature of the alloy
(b) What is the composition of this solid phase? (b) the composition of the liquid phase
(c) At what temperature does the liquid solidify? (c) the mass fractions of both phases
(d) What is the composition of this last remaining 9.22 A 40 wt% Pb–60 wt% Mg alloy is heated to
liquid phase? a temperature within the a liquid-phase re-