2. (a) Which statement is correct? i. Grain boundaries and dislocations are area

Question

2. (a) Which statement is correct? i. Grain boundaries and dislocations are area defects ii. Only dislocations are area defects. iii. Vacancies and substitutional solid solution atoms are point defects. iv. Dislocations and vacancies are point defects v. Self interstitial atoms and dislocations are point defects [1 mark] (b) For a three phase system (liquid and two solid phases, and ), write down the reaction of the eutectic type [1 mark] (c) Referring to Figure 1, below, draw a schematic of the phases (with labels) you would expect to see at Points A, C and E. 400 300 200 oa 19 183° 61.9 97 100 0 Pb 20 60 40 Weight percent tin 80 Sn Figure 1- Pb-Sn Phase Diagram [2 marks] SECTION A, Question 2, continued over page CONTINUED

Explanation / Answer

2. (a) iV Dislocations and vacancies are point defects because these happen due to deviations from the a point or an atom from the original crystal.

(b) the reaction is

liquid -------------------------> alpha solid soluton + beta solid solution (at eutectic temperature)

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