ATTEMPT ALL QUESTIONS. EACH CARRIES 1%; MAXIMUM POSSIBLE SCORE IS 10%.
ANSWER CONCISELY, TO THE POINT: BE BRIEF
| (1) | A hypothetical element crystallizes in the BBC structure but changes
to FCC at higher temperatures. The densities of its low- and high-temperature
phases are 8 and 2g cm-3, respectively. X-ray
diffraction determines that the BCC phase has a lattice constant of 2 A.
What is the predicted value for the FCC phase?
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| (2) | In a cubic crystal, what is the direction of the Burgers vector for
an edge dislocation that contains an extra half-plane of (101)?
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| (3) | Is it possible that silver metal has the slip system {111}<111>?
Explain your answer.
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| (4) | What is resolved shear stress on the {110}<111> slip
system, when 10M Pa is applied along the [010] direction?
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| (5) | Is it possible to work harden jade stone? Explain.
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| (6) | A phase transformation is known to obey the Avrami equation, with the
kinetic constant k depending exponentially on inverse temperature, and
n = 1. Show that the activation energy Q, in k, may be obtained by plotting
lnt£\ against 1/T, where t£\ is the time
taken to the fraction of transformation to reach the value£\(0¡Ù£\¡Ù)
when the temperature is T.
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| (7) | Name two common examples of ANY TWO of the followings:
ii. 1-dimensional defects; iii. 2-dimensional defects. |
| (8) | Name two techniques by which atoms in a solid may be imaged;
which one can show a moving dislocation?
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| (9) | Name three ways by which a polycrystalline metallic material
can be made stronger (greater yield strength); which one does
not
involve heat treatment?
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| (10) | A phase transformation that obeys the Avrami law is made to proceed
isothermally, at temperature To, Sketch the curve of transformation
fraction against time, schematically. This reaction is now made to proceed
at rising temperature, starting from To. In the same figure,
sketch the curve again for the latter case, to show an approximate relation
between the two plots.
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