Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Teaching & Learning Packages Ternary Phase Diagrams Summary
Ternary Phase Diagrams AimsBefore you startIntroductionRepresenting ternary phase diagramsSections through ternary phase diagramsTie lines and tie trianglesApplying the Gibbs phase rule to ternary systemsSolidification of ternary alloys – complete solid solutionSolidification of ternary alloys – one eutectic valleySolidification of ternary alloys – Class I reactionsSolidification of ternary alloys – Class II reactionsSolidification of ternary alloys – Class III reactionsCase Study: Sn-Ag-Cu systemUses of ternary alloysSummaryQuestionsGoing further
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Summary

This has been a brief introduction to the rich and interesting field of ternary phase diagrams.

Conventions for representing information on ternary systems (both as the whole space model and as sections taken through it) have been discussed. The trade-off of simplicity and information loss in taking sections through a complete space has been considered and the limitations of each kind of section should be appreciated.

The various kinds of equilibria (two-phase, three-phase, etc.) and how to determine the compositions and proportions of phases present using tie lines and tie triangles should be understood.

There should be an appreciation of how alloys solidify in a variety of simple ternary systems and the different kinds of invariant reactions ternary alloys can undergo:

Class I    \(\rm{ L \rightleftharpoons \alpha + \beta + \gamma} \)

Class II   \(\rm{ L + \alpha \rightleftharpoons \beta + \gamma} \)

Class III  \(\rm{ L + \alpha + \beta \rightleftharpoons \gamma} \)

Examples of industrially and scientifically important ternary systems have been provided to demonstrate both the applications of ternary phase diagrams and the complexities of real systems.

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