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

DoITPoMS Teaching & Learning Packages Ternary Phase Diagrams Questions
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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Questions

Quick questions

You should be able to answer these questions without too much difficulty after studying this TLP. If not, then you should go through it again!

  1. In a ternary system ABC at a specific temperature there is a three-phase equilibrium of α, β and γ such that the compositions of the phases (by weight) are:
    α  75% A  15% B  10% C
    β  20% A  50% B  30% C
    γ  5% A  30% B  65% C
    An alloy lies in this three-phase region. It consists of equal proportions of α, β and γ. What is its composition?

    a 33% A  32% B  35% C
    b 27% A  34% B  39% C
    c 49% A  26% B  25% C
    d 21% A  43% B  36% C

  2. A two-phase region exists in a ternary system. Which set (or sets – you may choose more than one) of variables can be used to define the system?

    a Temperature
    b Proportion of one component in one phase
    c Temperature and the proportion of one component in one phase
    d The proportion of two components in either of the two phases (or one of each)

Deeper questions

The following questions require some thought and reaching the answer may require you to think beyond the contents of this TLP.

  1. What is the composition of alloy X in the diagram below?

    (a) 70% A 20% B 10% C
    (b) 15% A 75% B 10% C
    (c) 40% A 55% B 20% C
    (d) 20% A 65% B 15% C

  2. Which of the following statements about vertical sections is incorrect?

    a Vertical sections show the solidus and liquidus temperatures
    b Compositions can be read off most vertical sections using horizontal tie lines
    c Vertical sections are perpendicular to the composition triangle
    d Vertical sections are pseudo binaries if they link two congruently melting solids

  3. Which of the following diagrams has possible tie lines shown?

    a
    b
    c
    d

  4. In the diagram below, which two phase fields are separated by the shaded surface?

    a L and L + β
    b L + α and α
    c α + β and α + β + γ
    d L and L + α

  5. During a univariant eutectic reaction (where a binary eutectic reaction is extended into the ternary space, shown by a eutectic valley) the proportions of phases present change as the reaction proceeds (the proportion of L decreases to zero and the proportions of the two solid phases increase). Why is this?

    a The bulk composition moves past the tie triangle on the composition triangle
    b The tie triangle and the bulk composition are both moving but at different rates so there is relative motion
    c The tie triangle moves past the stationary bulk composition
    d The tie triangle disappears when it reaches the bulk composition leaving a two-phase region.

  6. Which of the following is associated with a class II reaction?

    a
    b L + α + β → γ
    c
    d

  7. Consider a ternary phase diagram where one of the bounding binaries has a eutectic point and the other two show complete solid solubility. The diagram below shows such a system (the ternary space is left intentionally blank):

    Sketch what an isothermal section for this system might look like a) above the eutectic temperature but below the melting point of B b) below the eutectic temperature and c) below the melting point of C.

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