Grain boundaries

Which of the followings is not a cubic system

For a general plane {hkl} in the cubic system, there are 48 (24 pairs) variants. This number is sometimes known as the multiplicity and given the symbol mhkl

14. The shear stress required to move a dislocation through a crystal is called line defect ch 5

15. Dislocations are is a crystallographic defect, or irregularity, within a crystal structure. The presence of dislocations strongly influences many of the properties of materials.

Which of the following statements is incorrect for dislocations

In materials science, a dislocation is a crystallographic defect, or irregularity, within a crystal structure. The presence of dislocations strongly influences many of the properties of materials.

18. A screw dislocation can only change its slip plane by a process known as dislocation climb

19. Which of the followings is correct for edge dislocations: An edge dislocation is a defect where an extra half-plane of atoms is introduced mid way through the crystal, distorting nearby planes of atoms. When enough force is applied from one side of the crystal structure, this extra plane passes through planes of atoms breaking and joining bonds with them until it reaches the grain boundary.

20. The elastic strain energy around a dislocation is proportional to the square of the Burgers vector

21. Two oppositely signed dislocations sets of near-screw dislocations. If two dislocations of opposite sign meet then they effectively cancel out and their contribution to the stored energy is removed

22. Slip begins when between planes containing the smallest Burgers vector. Slip is the process by which plastic deformation is produced by a dislocation motion.

23. Easy glide'' is a term used to define the deformation occurring

24. Work hardening is the phenomenon whereby a ductile metal becomes harder and stronger as it is plastically deformed.

25. Larger the grain size - recrystallyzation.

26. Which of the following mechanisms can not occur in precipitate hardened polycrystalline metals

Precipitation hardening, also called age hardening, is a heat treatment technique used to increase the yield strength of malleable materials, including most structural alloys of aluminium, magnesium, nickel and titanium, and some stainless steels. It relies on changes in solid solubility with temperature to produce fine particles of an impurity phase, which impede the movement of dislocations, or defects in a crystal's lattice.

27. Strain rate is a product: strain rate is a rate of deformation

28. Which of the followings has the highest strength

29. Easy glide can only be seen in: The Action of a Glide: glide reflect about line/plane and translate by ½ lattice spacing

Grain boundaries

The grain boundary is the boundary separating two small grains or crystals having different crystallographic orientations in polycrystalline materials. Various degrees of crystallographic misalignment between adjacent grains are possible. When this orientation mismatch is slight, on the order of a few degrees, then the term small- (or low-) angle grain boundary is used. These boundaries can be described in terms of dislocation arrays. Tilt boundary; When the angle of misorientation is parallel to the boundary, a twist boundary results, which can be described by an array of screw dislocations.

31. Defects associated with one or two atomic positions are called ………

Imperfections Point defects

32. Carbon forms a(n) ………solid solution when added to iron

Carbon forms an interstitial solid solution when added to iron; the maximum concentration of carbon is about 2%.

33. ┴ + ┬ =.......................

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