Presentation Slip System

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

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. 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.

6. 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.

7. 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)

8. 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 i n front side

9. fcc 1. Unit cell of cubic geometry, with atoms located at each of the corners and centres of all cube faces. 2. The unit cell length a and atomic radius R is related through 3. Coordination number: 12 4. examples: copper, aluminium, silver Definition Coordination number: the number of attachments to the central atom in a coordination complex Unit cell: 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

10. BCC 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. The unit cell length a and atomic radius R is related through 3. Coordination number: 8 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

11. hcp 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. The short unit cell length, a and long unit cell length, c is related through (ideal value) 3. Coordination number: 12 4. examples: cadmium, magnesium, titanium.   (a) A reduced-sphere unit cell representation (b) An aggregate of many atoms

12. 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>

13. Crystallographic direction for hcp The 3 axes are all contained in single plane (basal plane), and 120 degree to each other. z-axis is perpendicular to basal plane  

14. Crystallographic planes Specified by Miller indices ( hkl )

15. Crystallographic plane for hcp Accomplished by Miller-Bravais system The convention use i is determined through    

16. Linear and planar densities Linear density (LD) is defined as   Planar density (PD) is defined as  

17. 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.

18. Types of slip systems

19. 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.

20. 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.

21. A table of slips system for fcc , bcc and hcp metals

22. 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

23. 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: