7. In the plastic deformation of a single crystal a. dislocations can be created

Question

7. In the plastic deformation of a single crystal a. dislocations can be created b. slip is not a factor c. vacancies are used for deformation to oceur. d. all of the above c none of the above. 8. As the grain size of a polycrystalline metal is decreased the tensile strength increases because a. the grain boundaries interrupt the slip. b. grain boundaries are areal defects that contains a large number of vacancies c. grain boundaries generate strain fieids that interact motion of dislocations d all of the above e. none of the above. 9. The Critical Resolved Shear Stress is a constant for a particular polycrystalline metal. a b. determined by the lattice type c. the stress that causes a metal to fracture d. applicable to single crystals only e the stress required to continue slip.

Explanation / Answer

7,a)In a plastic-deformation of a single crystal dislocation can be created.At RT the major source for plastic deformation is the dislocation motion through the crystal lattice. Dislocation motions occurs on fixed crystal planes (“slip planes”) in fixed crystallographic directions (corresponding to the Burgers vector of the dislocation that carries the slip).

8.d).all thabove

9.d)The stress required to initiate slip in a pure and perfect single crystal, the critical resolved shear stress (CRSS) is a constant for a material at a given temperature.

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