Question $1-15$ Marks

$1\mathrm{.}1$ The movement of partial dislocations during application of stress tends to create the

intrinsic stacking faults which raise the energy of the crystal. Briefly discuss three sources

of energy that creates the stacking fault energy. $(6)$

$1\mathrm{.}2$ Use relevant dislocation theories and explain why the strength of metals drops at higher

temperatures $(2).$

$1\mathrm{.}3$ Why will cross slip tends to be difficult in HCP materials $(2).$

$1\mathrm{.}4$ Why is it necessary for dislocations to have a smallest Burgers vector as possible $(2).$

$1\mathrm{.}5$ Explain why substitutional atoms prefer to accommodate themselves near dislocations

cores $(3)$

Question $2-45$ marks

$2\mathrm{.}1$ Find the partial dislocations formed from $($a$/2)\frac{01}{b}ar(1)$ on the $(\frac{?}{\text{b}\text{a}\text{r}}\frac{1}{b}ar\frac{1}{b}ar(1)$ in the FCC crystal

structure, you need to show the plane, slip directions and the directions of partials in a neat

diagram.

$2\mathrm{.}2$ Prove whether the reaction obtain in $2\mathrm{.}1$ will occur.

$2\mathrm{.}3$ Suppose a dislocation line coincide with one of the partials determine in $2\mathrm{.}1,$ do you

think it will be able to cross slip?

$2\mathrm{.}4$ A single crystalline metal rod of $0\mathrm{.}015$ m diameter is uni$-$axially loaded with a force of

$2120\mathrm{.}57$ N in $[1\frac{?}{\text{b}\text{a}\text{r}}(1)0$ direction. Given slip system as: $(\frac{1}{b}ar\frac{1}{b}ar(1))[\frac{0}{b}ar(1)1]$ and critical resolved shear

stress for this slip system as $6$ MPa $.$ Determine whether yielding will occur $(5).$