Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 9: Problem 28

Briefly explain why, upon solidification, an alloy of eutectic composition forms a microstructure consisting of alternating layers of the two solid phases.

Short Answer

Expert verified
Answer: An alloy of eutectic composition forms a microstructure consisting of alternating layers of the two solid phases upon solidification due to the eutectic reaction. As the alloy cools down to the eutectic temperature, the liquid simultaneously transforms into both solid phases, with the distinct solid phases growing in alternate layers of uniform thicknesses. This minimizes interfacial energy between the two solid phases and results in a lamellar or rod-like microstructure, depending on the specific alloy and growth conditions.

Step by step solution

01

Understand the eutectic reaction

A eutectic reaction is a three-phase equilibrium reaction in which a liquid phase forms two distinct solid phases upon cooling. In an alloy, this occurs at a specific eutectic composition and temperature. The eutectic composition represents a unique proportion of two elements, at which the lowest melting point is achieved.
02

Formation of an alloy's microstructure during solidification

When an alloy solidifies, the microstructure is composed of two solid phases corresponding to the elements present in the alloy. During solidification, the two solid phases grow simultaneously. As the temperature drops, the solid-liquid equilibrium is maintained, and the levels of each element in the solid and liquid phases are altered.
03

Eutectic solidification

As the eutectic alloy cools down to the eutectic temperature, the liquid begins to transform simultaneously into the two solid phases. Due to the difference in diffusion rates, the solid phases grow into alternate layers with relatively uniform thicknesses. This happens because both solid phases want to minimize the interfacial energy between them by forming thin layers.
04

Eutectic microstructure

Upon reaching the eutectic temperature, the remaining liquid undergoes eutectic solidification, and the alternating layers of the two solid phases continue to form until the entire liquid phase solidifies. This results in a microstructure consisting of alternating layers of the two solid phases as a direct outcome of the eutectic reaction. The layers tend to have a lamellar or rod-like appearance depending on the specific alloy and growth conditions.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Consider the hypothetical eutectic phase diagram for metals A and B, which is similar to that for the lead-tin system, Figure 9.8. Assume that (1) \(\alpha\) and \(\beta\) phases exist at the A and B extremities of the phase diagram, respectively; (2) the eutectic composition is 47 wt \(\%\) B-53 wt \% A; and (3) the composition of the \(\beta\) phase at the eutectic temperature is \(92.6 \mathrm{wt} \%\) B-7.4 wt \(\% \mathrm{~A}\). Determine the composition of an alloy that will yield primary \(\alpha\) and total \(\alpha\) mass fractions of \(0.356\) and \(0.693\), respectively.

(a) Briefly describe the phenomenon of coring and why it occurs. (b) Cite one undesirable consequence of coring.

Two intermetallic compounds, \(\mathrm{AB}\) and \(\mathrm{AB}_{2}\), exist for elements \(\mathrm{A}\) and \(\mathrm{B}\). If the compositions for \(\mathrm{AB}\) and \(\mathrm{AB}_{2}\) are \(34.3 \mathrm{wt} \% \mathrm{~A}-65.7\) \(\mathrm{wt} \% \mathrm{~B}\) and \(20.7 \mathrm{wt} \% \mathrm{~A}-79.3 \mathrm{wt} \% \mathrm{~B}\), respectively, and element \(\mathrm{A}\) is potassium, identify element B.

Given here are the solidus and liquidus temperatures for the germanium-silicon system. Construct the phase diagram for this system and label each region. $$ \begin{array}{ccc} \hline \begin{array}{c} \text { Composition } \\ (\boldsymbol{w t} \% \text { Si) } \end{array} & \begin{array}{c} \text { Solidus } \\ \text { Temperature }\left({ }^{\circ} \mathrm{C}\right) \end{array} & \begin{array}{c} \text { Liquidus } \\ \text { Temperature }\left({ }^{\circ} \mathrm{C}\right) \end{array} \\ \hline 0 & 938 & 938 \\ 10 & 1005 & 1147 \\ 20 & 1065 & 1226 \\ 30 & 1123 & 1278 \\ 40 & 1178 & 1315 \\ 50 & 1232 & 1346 \\ 60 & 1282 & 1367 \\ 70 & 1326 & 1385 \\ 80 & 1359 & 1397 \\ 90 & 1390 & 1408 \\ 100 & 1414 & 1414 \\ \hline \end{array} $$

Construct the hypothetical phase diagram for metals \(A\) and \(B\) between temperatures of \(600^{\circ} \mathrm{C}\) and \(1000^{\circ} \mathrm{C}\) given the following information: \- The melting temperature of metal \(A\) is \(940^{\circ} \mathrm{C} .\) \- The solubility of \(\mathrm{B}\) in \(\mathrm{A}\) is negligible at all temperatures. \- The melting temperature of metal \(\mathrm{B}\) is \(830^{\circ} \mathrm{C}\). \- The maximum solubility of \(\mathrm{A}\) in \(\mathrm{B}\) is 12 wt \(\%\) A, which occurs at \(700^{\circ} \mathrm{C}\). \- At \(600^{\circ} \mathrm{C}\), the solubility of \(\mathrm{A}\) in \(\mathrm{B}\) is \(8 \mathrm{wt} \% \mathrm{~A}\). \- One eutectic occurs at \(700^{\circ} \mathrm{C}\) and \(75 \mathrm{wt} \%\) B- \(25 \mathrm{wt} \% \mathrm{~A}\) \- A second eutectic occurs at \(730^{\circ} \mathrm{C}\) and 60 \(\mathrm{wt} \% \mathrm{~B}-40 \mathrm{wt} \% \mathrm{~A}\). \- A third eutectic occurs at \(755^{\circ} \mathrm{C}\) and 40 \(\mathrm{wt} \%\) B-60 wt \(\% \mathrm{~A}\). \- One congruent melting point occurs at \(780^{\circ} \mathrm{C}\) and \(51 \mathrm{wt} \%\) B-49 wt \(\% \mathrm{~A}\). \- A second congruent melting point occurs at \(755^{\circ} \mathrm{C}\) and \(67 \mathrm{wt} \%\) B-33 wt \(\% \mathrm{~A}\). \- The intermetallic compound \(\mathrm{AB}\) exists at \(51 \mathrm{wt} \%\) B-49 wt \% A. \- The intermetallic compound \(\mathrm{AB}_{2}\) exists at \(67 \mathrm{wt} \%\) B-33 wt \(\% \mathrm{~A}\).
See all solutions

Recommended explanations on Physics Textbooks

Fields in Physics

Read Explanation

Engineering Physics

Read Explanation

Magnetism and Electromagnetic Induction

Read Explanation

Magnetism

Read Explanation

Dynamics

Read Explanation

Measurements

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free