Figure 9.36 is the tin-gold phase diagram, for which only...

Name: Problem 42, Chapter 9: Materials Science and Engineering. An Introduction
Uploaded: 2021-11-04T12:21:40-08:00
Duration: 4 min 29 s
Channel: Ameer Said
Description: Figure 9.36 is the tin-gold phase diagram, for which only single-phase regions are labeled. Specify temperature-composition points at which all eutectics, eutectoids, peritectics, and congruent phase transformations occur. Also, for each, write the reaction upon cooling.

Figure 9.36 is the tin-gold phase diagram, for which only single-phase regions are labeled. Specify temperature-composition points at which all eutectics, eutectoids, peritectics, and congruent phase transformations occur. Also, for each, write the reaction upon cooling.

Key Concepts

Binary Phase Diagrams

Binary phase diagrams graphically represent the equilibrium between phases in a system containing two components. These diagrams are plotted with temperature on one axis and the composition of one component on the other. They show the stability regions of distinct phases and allow prediction of microstructural evolution during cooling or heating through the identification of phase boundaries such as liquidus, solidus, and invariant points.

Eutectic Reaction

A eutectic reaction is an invariant reaction in a binary phase diagram where, upon cooling, a liquid transforms into two distinct solid phases simultaneously at a specific composition and temperature. This reaction is characterized by its unique composition where the mixture has the lowest melting point, leading to a fine and interlocked microstructure.

Eutectoid Reaction

A eutectoid reaction is a reaction that takes place entirely within the solid state, where one solid phase decomposes into two different solid phases upon cooling at a fixed composition and temperature. This reaction leads to a characteristic microstructure and is analogous to a eutectic reaction but occurring between solid phases.

Peritectic Reaction

A peritectic reaction involves a reaction between a liquid and a solid phase, which upon cooling, reacts to form a new solid phase. This invariant reaction in a binary system occurs at a specific composition and temperature and typically results in a mixture of phases that can be sensitive to processing conditions.

Congruent Phase Transformation

A congruent phase transformation is a process where a phase converts to another phase, such as a solid to liquid or vice versa, without any change in composition. This transformation occurs at a specific temperature and is characterized by the direct melting or crystallization of a pure phase, leading to significant implications in the processing and purity of materials.

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