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Chapter 9: Problem 3
Cite three variables that determine the microstructure of an alloy.
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For alloys of two hypothetical metals \(\mathrm{A}\) and \(\mathrm{B}\), there exist an \(\alpha\), A-rich phase and a \(\beta\), B-rich phase. From the mass fractions of both phases for two different alloys provided in the following table (which are at the same temperature), determine the composition of the phase boundary (or solubility limit) for both \(\alpha\) and \(\beta\) phases at this temperature. $$ \begin{array}{lcc} \hline \begin{array}{c} \text { Alloy } \\ \text { Composition } \end{array} & \begin{array}{c} \text { Fraction } \\ \boldsymbol{\alpha} \text { Phase } \end{array} & \text { Fraction } \\ \hline 70 \mathrm{wt} \% \mathrm{~A}-30 \mathrm{wt} \% \mathrm{~B} & 0.78 & 0.22 \\ \hline 35 \mathrm{wt} \% \mathrm{~A}-65 \mathrm{wt} \% \mathrm{~B} & 0.36 & 0.64 \\ \hline \end{array} $$
A steel alloy contains \(95.7 \mathrm{wt} \% \mathrm{Fe}, 4.0 \mathrm{wt} \% \mathrm{~W}\), and \(0.3 \mathrm{wt} \% \mathrm{C}\). (a) What is the eutectoid temperature of this alloy? (b) What is the eutectoid composition? (c) What is the proeutectoid phase? Assume that there are no changes in the positions of other phase boundaries with the addition of \(\mathrm{W}\).
The mass fractions of total ferrite and total cementite in an iron-carbon alloy are \(0.91\) and \(0.09\), respectively. Is this a hypoeutectoid or hypereutectoid alloy? Why?
Cite the phases that are present and the phase compositions for the following alloys: (a) \(15 \mathrm{wt} \% \mathrm{Sn}-85 \mathrm{wt} \% \mathrm{~Pb}\) at \(100^{\circ} \mathrm{C}\left(212^{\circ} \mathrm{F}\right)\) (b) \(25 \mathrm{wt} \% \mathrm{~Pb}-75 \mathrm{wt} \% \mathrm{Mg}\) at \(425^{\circ} \mathrm{C}\left(800^{\circ} \mathrm{F}\right)\) (c) \(85 \mathrm{wt} \% \mathrm{Ag}-15 \mathrm{wt} \% \mathrm{Cu}\) at \(800^{\circ} \mathrm{C}\left(1470^{\circ} \mathrm{F}\right)\) (d) \(55 \mathrm{wt} \% \mathrm{Zn}-45 \mathrm{wt} \% \mathrm{Cu}\) at \(600^{\circ} \mathrm{C}\left(1110^{\circ} \mathrm{F}\right)\) (e) \(1.25 \mathrm{~kg} \mathrm{Sn}\) and \(14 \mathrm{~kg} \mathrm{~Pb}\) at \(200^{\circ} \mathrm{C}\left(390^{\circ} \mathrm{F}\right)\) (f) \(7.6 \mathrm{lb}_{\mathrm{m}} \mathrm{Cu}\) and \(144.4 \mathrm{lb}_{\mathrm{m}} \mathrm{Zn}\) at \(600^{\circ} \mathrm{C}\left(1110^{\circ} \mathrm{F}\right)\) (g) \(21.7 \mathrm{~mol} \mathrm{Mg}\) and \(35.4 \mathrm{~mol} \mathrm{~Pb}\) at \(350^{\circ} \mathrm{C}\left(660^{\circ} \mathrm{F}\right)\) (h) \(4.2 \mathrm{~mol} \mathrm{Cu}\) and \(1.1 \mathrm{~mol} \mathrm{Ag}\) at \(900^{\circ} \mathrm{C}\left(1650^{\circ} \mathrm{F}\right)\)
For an iron-carbon alloy of composition 3 wt \(\%\) C-97 wt \% Fe, make schematic sketches of the microstructure that would be observed for conditions of very slow cooling at the following temperatures: \(1250^{\circ} \mathrm{C}\left(2280^{\circ} \mathrm{F}\right), 1145^{\circ} \mathrm{C}\left(2095^{\circ} \mathrm{F}\right)\), and \(700^{\circ} \mathrm{C}\left(1290^{\circ} \mathrm{F}\right)\). Label the phases and indicate their compositions (approximate).
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