This document discusses the atomic structure and classification of materials. It begins by classifying materials as either crystalline or non-crystalline based on the repeating patterns of their atomic structures. Crystalline materials have symmetric, repeating atomic positions while non-crystalline materials do not. The document then discusses various aspects of crystalline structure including unit cells, lattice constants, space lattices, and common crystal structures. It also covers crystal imperfections such as point defects, line defects, and surface defects. Finally, the mechanisms of plastic deformation through slip and twinning are summarized.

1. Crystalline Str. Of Metal And
Material

2. Atomic Structure

3. Classification of material according
to it’s structure
1. Crystalline Material
2. Non- Crystalline Material

4. Crystalline Material
• In Crystalline Material atoms position are
repeating and symmetric over a large atomic
distance.

5. Crystalline Material

6. Non-crystalline Material
• In Non- Crystalline Material atoms position are
non-repeating and non-symmetric over a large
atomic distance

7. Non-crystalline Material

8. Unit Cell
• It is the smallest arrangement of an atom,
molecule which is true representation of
crystal structure

9. Unit Cell

10. Lattice Angle
• It is the angle between edge of unit cell

11. Lattice Constant
• It is the distance between the centers of two
adjacent atoms in a unit cell.

12. Space /Crystal Lattice
• It is the three dimensional arrangement of
imaginary line connecting the unit cells in
space

13. Type Of Crystals
• Simple Cubic Crystal:

14. Tetragonal

15. Hexagonal

16. Orthorhombic

17. Rhombohedral

18. Monoclinic

19. Triclinic

20. Type of Crystal Structure
• Simple Cubic Crystal Structure ( S.C.C.)
• Body Centered Crystal Structure ( B.C.C)
• Face Centered Crystal Structure (F.C.C.)
• Hexagonal Close Packed Structure ( H.C.P)

21. Simple Cubic Crystal Structure

22. Body Centered Crystal Structure
( B.C.C)

23. Face Centered Crystal Structure
(F.C.C.)

24. Hexagonal Close Packed Crystal Str.
(H.C.P.)

25. Crystal Imperfections
• Any deviations from the perfect arrangement
of atoms in a crystal are called crystal defects.
• A crystal defect is a lattice irregularity having
one or more of its dimensions on the order of
an atomic diameter.
• Imperfections have a significant impact on the
characteristics of some materials

26. Crystal imperfections
Point
Defect
Line
Defect
Surface
Defect

27. Point Defects
a) b)

28. Point Defects
Defects generate due to imperfect packing of the
atoms during crystallization or solidification are
known as point defects.
Types of Point Defect
1. Vacancy defect
2. Self Interstitial defect
3. Interstitial defect
4. substitutional defect

29. Vacancy Defect
• When one or more atoms are missing from a
normally occupied positions in a crystal
arrangement , the defect developed are called
as Vacancy
• Caused due to imperfect packing of atoms or
thermal vibrations of atoms at high temp.
• Vacancy results in tensile stress field around
vacancy.

30. Vacancy defect

31. Interstitial defect
• When an atom occupies the interstitial location
of the lattice structure, an interstitial defect
develops. This interstitial atom might come from
the same crystal or another substance.
Accordingly, there are two types of interstitial
defects:
• Self-Interstitial Defect - When an atom from the
same crystalline solid occupies an interstitial
location instead of its original lattice site, this is
known as a self-interstitial defect.
• Interstitial Defect- A foreign atom occupying the
interstitial location causes an interstitial defect.

32. Self Interstitial defect

33. Interstitial defect
• Foreign atom occupy interstitial site of atomic
str.

34. Substitutional defect

35. Line defects or 1D Defect
• Line defect arise due to addition or deletion
line of atom from its designated position.
• The line defect is also called as dislocation.
• Line defect causes due to growth accidents,
thermal stresses and external stresses.
• Burger’s Vector and Circuit
It indicates the direction and magnitude of the
shift that occurred around the slip p[lane due to
presence of dislocation

36. Burger’s Vector and Circuit
NO Defect Line Defect

37. Type of line defect
• Edge Dislocation
• Screw Dislocation

38. Edge Dislocation
• If insertion of extra half plane line of atom is inserted between
the planes of atoms in a perfect crystal the defect produced is
called edge dislocation.
• If insertion of extra half plane line of atom is on Upper side
then it is called as Positive dislocation- ⊥
• If insertion of extra half plane line of atom is on bottom side
then it is called as negative dislocation- T

39. Screw Dislocation
• When atoms are displaced in two separate
planes perpendicular to each other, the defect
is known as Screw dislocation.
• Shear stress displaces the structure and
causes dislocation.
• The dislocation displacement follows the
helical or screw path, so it is called as Screw
dislocation
• Produced in metals during crystal growth

40. Screw Dislocation
• .

41. Effect of line defects
• Improve mechanical properties of material
• Increase electrical resistance in material
• Decrease corrosion resistance in material
• Increase recrystallisation temp.

42. Surface Defect
• The defects which takes place on the surface of
material are called surface defects
• Occurs due to imperfect packing of atoms during
solidification or due to defective orientation of
the surface.
• Types
• Grain Boundary defect
• Twin Boundary defect
• Low Angle Boundary Defect
• Stacking Defect

43. Grain Boundary defect
• When some of the grains have different
orientation than general pattern of grains ,
then such imperfection is known as Grain
Boundary defect.
• The crystal orientation change abruptly at
grain boundary
• Grain boundary energy is responsible for grain
growth on heating

45. Twin Boundary Defect
• Is Planer surface defect
• It may result during crystal growth or
deformation of materials
• Twin boundaries occurs in pairs.
• Twin boundaries can be seen easily using
optical microscope.

46. Twin Boundaries defect
• It produced due to shear force.
• In twin boundary defect mirror image of miss
orientation is form.

47. Low angle boundary defect
• It associate with mismatch between two
adjacent grain.

48. • It is a surface defect
• Also known as Tilt Boundary
• Disruption in the boundary is not so severe as
in case of High angle boundary.

49. Stacking Defect
• It is a surface defect
• Regular order of atomic structure is disturbed
• It associate with change in stacking sequence
in crystalline str.
• Stacking fault occurs in FCC metals

51. Deformation in Material
• Elastic Deformation: Stress below the elastic
limit.
• Plastic Deformation: Stress above the elastic
limit.

52. Mechanism of Plastic Deformation
• Slip
• Twinning

53. Slip
• Slip is define as permanent shear displacement
of one part of the crystal relative to other.

54. Twin
• In twin boundary defect mirror image of miss
orientation is form.

55. Deformation by Slip
• Slip is most important mechanism of plastic
deformation
• Slip involves dislocation on slip planes.
• Slip is cause4d by shear stresses(at the level of
the slip plane).
• A slip system consists of slip direction lying on
slip planes.

56. Mechanism of slip
• Slip is prominent mechanism of plastic
deformation
• It involves sliding of blocks of crystal over one
another along definite crystallographic planes.
• It is similar to deck of cards, when it is pushed
from one end.
• During slip each atom moves same integral
number of atomic distance along the slip plane
forming a step
• But orientation of the crystal remains same.

57. Deformation by twining
• It is a plastic deformation
• Takes place due to set of forces applied on a given
metal piece.
• A metal deforms by twinning only if it is unable to
deform by slip.
• In twinning deformation causes changes in plane
orientation.
• Twinning may be produced by mechanical
deformation or annealing
• Mechanical twinning
• Annealing Twinning

58. Sr No Basis Slip Twinning
1
Mechanism deformation takes by sliding of atoms
over one another
Deformation takes place along two
planes due to set of forces
2 Distance
Atomic movements are over large
distance.
Atomic movements are over a
fraction of atomic spacing .
3 Stress Requires low stress Requires high stress
4 Steps
Produces series of small steps like
structure
It produces small but continuous
deformation
5 Orientation
Crystallographic orientation above and
below the slip plane is the same both
before and after deformation Reorientation across the twin planes
6 Crystal Structure Mostly seen in BCC and FCC structure Mostly seen in HCP structure
7 Def
8 Diagram

59. Fracture