Question

1.1 Which of the following is NOT a combination of slip planes and slip directions of FCC? (A) (111) [10i] (8) (111) (T10] 1.2 Which of the following best explains why FCC metals (Cu, Al, Ni, Ag, Au) are of higher ductility than HCP metals (Mg, Ti, Zn)? (A) Because FCC metals have more free electrons to move around and facilitate dislocation motion; (B) Because FCC metals have more number of slip systems (i.e. slip planes and slip directions) (C) Because FCC metals have lower yield strengths; (D) Because FCC metals have less defects 1.3 Which of the following statements best describes the strengthening mechanism of metals? (A) When grain size is reduced, the increased number of grain boundaries acts as barriers for dislocation motion. (B) In solid solutions, solute atoms act as barriers for dislocation motion. (C) In strain (work) hardening, the increased number of dislocations repulse each other and hinder the dislocation motion. (D) All of above.

Answer 1

1.1) slip direction of <111> is not possible in fcc crystal, this direction is present in bcc

so answer is option D

1.2) usually it is seen that metals ith higher number of slip system has higher ductility because more number of disslocation arises under load.

so answer is option B

1.3) when any process cause a hinderence or obstruction in the movement of dislocations then higher force is required to move the dislocation, an this increses the strength of metal.

so in the given processes all the process cause a obstruction to the movement of dislocation.

so answer is option D