OUTCOMES: -Describes slips plane and slips direction -Explain the types of dislocation. -Understand the metallic crystal structure, FCC, BCC and HCP -Understand the crystallographic direction and planes, and able to find the linear and planar density -Explain about slip systems, the way to determine it and its effect on the metal characteritcs.

1. What is slip?
Slip is lose one's footing and slide unintentionally for a
short distance… or to fall down.
SLIP SYSTEM

2. CONCEPT
Describes slips plane and slips direction
Explain the types of dislocation.
Understand the metallic crystal structure, FCC, BCC and HCP
Understand the crystallographic direction and planes, and able
to find the linear and planar density
Explain about slip systems, the way to determine it and its effect
on the metal characteritcs.

3. SLIP PLANES
• A plane surface through a
crystal along which slip can
take place under some
conditions without apparently
disrupting the crystal.
• Slip planes are the plane with
the highest density of atoms.

4. SLIP DIRECTION
Defintion:
• The direction in which the dislocation moves, which is the direction of
the Burgers vector for edge dislocations.
Burgers vector:
• the magnitude and direction of the lattice distortion resulting from a
dislocation in a crystal lattice.
• Uni-directional.

5. Types of
Dislocations
Edge dislocation
Screw dislocation

6. EDGE DISLOCATIONS
• One of the most common crystal
structure defects is edge
dislocations.
• This type of dislocation occurs
when there are extra atoms
inserted into a plane in the crystal
lattice.

7. SCREW DISLOCATION
• Defined as a dislocation in the lattice structure of a crystal in which the
atoms are arranged in a helical pattern that is normal to the direction of
the stress.
• The motion of screw dislocation is also a result of shear stress.
• Motion is perpendicular to the direction of stress.

8. CLOSE-PACKING OF EQUAL SPHERES
• In geometry, close-packing of equal spheres is a dense arrangement of
congruent spheres in an infinite, regular arrangement or lattice.
• We will discuss at the 3 most common metallic crystal structure.
Face-centred cubic crystal structure
(FCC)
Body-centred cubic crystal structure (BCC)
Hexagonal close-packed
crystal structure (HCP)

9. FCC
• Face-Centred Cubic (FCC) is a crystal structure found for many metals
that has a unit cell of cubic geometry with atoms located at each of the
corners and the centres of all the cube faces.
above
in front
side

10. FCC
1. 1. Unit cell of cubic geometry, with atoms
located at each of the corners and centres of
all cube faces.
2. 2. The unit cell length a and atomic radius R is
related through
3. 𝑎 = 2𝑅 2
4. 3. Coordination number: 12
5. 4. examples: copper, aluminium, silver
6. Definition
7. Coordination number:
8. the number of attachments to the central atom
in a coordination complex
9. Unit cell:
10. Small repeated entities that is subdivided from
the structure of atomic arrangement.
(a) A hard sphere-unit cell
representation
(b) A reduced-sphere unit cell
representation
(c) An aggregate of many atoms

11. BCC
1. 1. Consist of a single atom at the centre of unit
cell, surrounded by 8 one quarter of atoms,
each shared among 8 unit cells.
2. 2. The unit cell length a and atomic radius R is
related through
3. 𝑎 =
4𝑅
3
4. 3. Coordination number: 8
5. 4. examples: Chromium, iron, tungsten
(a) A hard sphere-unit cell
representation
(b) A reduced-sphere unit cell
representation
(c) An aggregate of many atoms

12. HCP
1. 1. Consist of 6 atoms that form hexagons and
surround a single atoms at the centre of top
and bottom face. In between top and bottom
faces, there is a plane consist of 3 additional
atoms
2. 2. The short unit cell length, a and long unit
cell length, c is related through
3.
𝑐
𝑎
= 1.633 (ideal value)
4. 3. Coordination number: 12
5. 4. examples: cadmium, magnesium, titanium.
(a) A reduced-sphere unit cell
representation
(b) An aggregate of many atoms

13. CRYSTALLOGRAPHIC
DIRECTION
Defined as a line between two
points, or a vector.
Denoted as [uvw], u,v,w are
reduce projections along xyz axis.
Equivalent direction can be
grouped into family in < >
Example: [100],[010],[001] can be
grouped as <100>

14. CRYSTALLOGRAPHIC
DIRECTION FOR HCP
• The 3 𝑎1, 𝑎2 𝑎𝑛𝑑 𝑎3 axes are
all contained in single plane
(basal plane), and 120 degree
to each other.
• z-axis is perpendicular to
basal plane

15. CRYSTALLOGRAPHIC
PLANES
Specified by Miller
indices (hkl)

16. CRYSTALLOGRAPHIC PLANE
FOR HCP
Accomplished by Miller-Bravais system
The convention use (ℎ𝑘𝑖𝑙)
i is determined through
𝑖 = − ℎ + 𝑘
ℎ = 1
𝑘 = −1
𝑙 = 1
𝑖 = − ℎ + 𝑘
𝑖 = 0
ℎ𝑘𝑖𝑙 𝑖𝑛𝑑𝑖𝑐𝑒𝑠 𝑎𝑟𝑒 (1101)

17. LINEAR AND PLANAR DENSITIES
• Linear density (LD) is defined as
• 𝐿𝐷 =
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑎𝑡𝑜𝑚𝑠 𝑐𝑒𝑛𝑡𝑟𝑒𝑑 𝑜𝑛 𝑑𝑖𝑟𝑒𝑐𝑡𝑖𝑜𝑛 𝑣𝑒𝑐𝑡𝑜𝑟
𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑑𝑖𝑟𝑒𝑐𝑡𝑖𝑜𝑛 𝑣𝑒𝑐𝑡𝑜𝑟
• 𝐿𝐷110 =
2 𝑎𝑡𝑜𝑚𝑠
4𝑅
=
1
2𝑅
• Planar density (PD) is defined as
• 𝑃𝐷 =
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑎𝑡𝑜𝑚𝑠 𝑐𝑒𝑛𝑡𝑟𝑒𝑑 𝑜𝑛 𝑝𝑙𝑎𝑛𝑒
𝑎𝑟𝑒𝑎 𝑜𝑓 𝑝𝑙𝑎𝑛
• 𝑃𝐷 = (2 𝑎𝑡𝑜𝑚𝑠)/8𝑅2
2

18. SLIP SYSTEM
• Dislocation does not move at the same degree of ease on all
crystallographic planes and direction of atoms
• The preferred plane with specified directions along which dislocation
motion occurs is called slip plane.
• The direction of the dislocation movement on slip plane is known as slip
direction.
• The combination of slip plan and slip direction is know as slip system.
• For a particular crystal structure:
• Slip plane: plane with greatest planar density
• Slip direction: direction with the highest linear density in slip plane.

19. TYPES OF SLIP SYSTEMS
• Have 12 slip systems
• Includes metals like copper, aluminium, nickel and silver
Face-centred cubic
(FCC) slip
• Have 12 to 24 slip systems
• Includes a wide range of metal alloys
Body-centred cubic
(BCC) slip
• Presents much less slip system than BCC and FCC crystal structures
• Includes metals like titanium, magnesium and zinc
Hexagonal close
packed (HCP) slip

20. FACE-CENTRED CUBIC (FCC) SLIP SYSTEM
Definition:
• Slip in face centered cubic (fcc) crystals occurs along the close packed
plane.
Lattice configuration of the close packed slip plane in an
FCC material. The arrow represents the Burgers vector in
this dislocation glide system.

21. FCC SLIP SYSTEM
• The slip plane belongs to the {111}
family
• Slips occur at <110>-type direction,
within {111} planes
• There are several slips direction for a
slip plane, forming different possible
combination of slip system
• For FCC, 4 unique {111} planes and 3
independent <110> directions, results
in 12 slips system.

22. A TABLE OF SLIPS SYSTEM FOR FCC, BCC
AND HCP METALS

23. FCC & BCC
• More slip systems, at lease 12
• Metal is ductile
• Plastic deformation is possible along
various systems.
• Less slip systems
• Metal is brittle
• Plastic deformation is less possible in
various systems.
HCP
COMPARISON OF NUMBER OF SLIPS
SYSTEM OF FCC,BCC WITH HCP

24. BURGERS VECTOR
• Defined as the magnitude of direction of lattice distortion associated
with a dislocation
• In slip system:
• Burgers vector direction is correspond to the dislocation slip direction
• Magnitude of Burgers vector is equal to the unit slip distance.
• Expressing Burgers vector, b in terms of unit cell length:
• 𝒃 < 𝐹𝐶𝐶 > =
𝑎
2
< 110 >
• 𝒃 < 𝐵𝐶𝐶 > =
𝑎
2
< 111 >
• 𝒃 < 𝐻𝐶𝑃 > =
𝑎
3
< 11 𝟐0 >