Your SlideShare is downloading. ×
5 Defects In Crystals  @ Www 07 Met Tk
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

5 Defects In Crystals @ Www 07 Met Tk

6,979
views

Published on

Published in: Technology, Business

0 Comments
5 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total Views
6,979
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
0
Comments
0
Likes
5
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. Imperfection /Defects All About Metallurgical & Materials Engineering Download This & More Stuff @ WWW.07MET.TK
  • 2. Structure -insensitive Properties
    • Elastic constants
    • Melting point
    • Density
    • Specific heat
    • Coefficient of thermal expansion.
  • 3. Structure-sensitive Properties
    • Electrical conductivity
    • Semiconductor Properties
    • Yield stress
    • Fracture Strength
    • Creep strength
    • Practically all the mechanical properties are structure-sensitive properties.
  • 4. Defects in Crystalline Materials
    • All real crystals contain imperfections which may be point, line , surface or volume defects.
    • Which disturb locally the regular arrangement of the atoms.
    • Their presence can significantly modify the properties of crystalline solids.
  • 5. Defect, or imperfection
    • The term defect, or imperfection, is generally used to describe any deviation from an orderly array of lattice points.
  • 6. point defect, or point imperfection
    • When the deviation from the periodic arrangement of the lattice is localized to the vicinity of only a few atoms it is called a point defect, or point imperfection.
  • 7. Lattice Imperfection
    • However if the defects extends through microscopic region of the crystal, it is called a lattice imperfection.
    • Lattice imperfections may be divided into Line defects and surface or Plane, defects.
  • 8. Types of defects *D=dimensional
  • 9. Point Defects
  • 10. Point Defects
  • 11. Line Defect
    • Line defects obtain their name because they propagate as lines or as a two dimensional net in the crystal. The edge and Screw dislocations are the common line defects encountered in materials.
    • Surface defects arise from the clustering of line defects into plane
  • 12.  
  • 13. Surface Defect
    • The stacking fault between two closed -packed regions of the crystal that have alternate stacking sequences are other example of surface defects.
    • Grain boundaries, a low angle boundaries and Twin boundaries are surface defects.
  • 14. Point Defects
    • All the atoms in a perfect lattice are at specific atomic sites (ignoring thermal vibrations).
    • In pure metal two types of point defect are possible,
    • i) Intrinsic defects ii) Extrinsic defects.
    • Intrinsic defects: i) A vacant atomic site or vacancy, ii) an interstitial atom.
    • Vacancy formed by the removal of an atom from an atomic site .
    • Interstitial by the introduction of an atom into a non- lattice site at 1/2, 1/2, 0 position.
  • 15. Point Defects
  • 16. Vacancy & Interstitial
    • It is known that vacancies and interstitials can be produced in materials by plastic deformation and high- energy particle irradiation.
    • The latter process is particularly important in materials in nuclear reactor installations.
    • The interstitial defect occurs in pure metals as a result of bombardment with high-energy nuclear particles ( radiation damage), but it does not occur frequently as a result of thermal activation.
    • Further more, intrinsic point defects are introduced into crystals simply by virtue of temperature, for all temperature above 0K there is a thermodynamically stable concentration.
  • 17.
    • The formation energy of interstitial is typically two to four times more than the formation energy of vacancy.
    • Therefore in metals in thermal equilibrium the concentration of intestinal may be neglected in comparison with that of vacancies
  • 18. Extrinsic defects
    • Extrinsic defects . Impurity atoms in a crystal can be considered as a extrinsic point defect. Impurity atoms can take up two different types of sites.
    • Substitutional. An atom of the parent lattice lying in a lattice site is replaced by the impurity atom
    • Interstitial The impurity atom is at a non- lattice site
  • 19. Point Defects
  • 20.  
  • 21. Dislocation
    • The most important two dimensional, or line, defect is the dislocation.
    • Dislocations are important for explaining the slip of crystals,
    • They are also intimately connected with nearly all other mechanical phenomena such as , the yield point, strain hardening /work hardening, creep, fatigue, and brittle fracture.
  • 22.  
  • 23.  
  • 24.  
  • 25.
    • One way of thinking of a dislocation is to consider that it is the region of localized lattice disturbance separating the slipped and un slipped region of a crystal.
  • 26.
    • The two basic types of dislocations :
    • Edge dislocation ; Burger vector is normal to the line of the dislocation.
    • Two types: Positive edge dislocation and negative edge dislocation.
    • Screw dislocation; Burger vector is parallel to the line of dislocation.
    • Two types: Right hand screw and left hand screw dislocation.
  • 27.
    • Two important rules.
    • I) The burger vector of edge dislocation is normal to the line of the dislocation .
    • II) The burger vector of screw dislocation is parallel to the line of the dislocation .
    • All crystals, apart from some whiskers, contain dislocations and in well annealed crystals the dislocation are arranged in a rather ill- defined net work, the frank net.
  • 28. Dislocation Density
    • The dislocation density is defined as the total length of dislocation line per unit volume of crystal, normally quoted in units of mm-2.
    • Thus for a volume V containing line length l, Density = l/V.
    • An alternative definition, the number of dislocations intersecting a unit area, again measured in units of mm-2 .
    • If all the dislocations are parallel, the two density values are the same, but for completely random arrangement the volume density is twice the surface density.
  • 29. Stacking Faults
    • A stacking fault is a planer defects ,
    • it is a local region in the crystal where the regular sequence has been interrupted.
    • The atomic arrangement on the plane of an fcc structure and the plane of an hcp structure could be obtained by the stacking of closed- packed planes of spheres.
    • For the fcc structure, the stacking sequence of the planes of atom is given by ABCABCABC.
    • For the hcp structure, the sequence is given by ABABAB and there is no alternate site for an A layer resting on B layer.
  • 30.
    • For the hcp structure, the sequence is given by ABABAB and there is no alternate site for an A layer resting on B layer. In case of ABCABCABC stacking, A layer can rest equally well on either B or C position and geometrically there is no reason for the selection of a particular position.
    • Therefore in fcc lattice two types of stacking fault are possible. Either by removal or introduction of stacking sequence.
  • 31.
    • i) Intrinsic stacking fault part of the layer has been removed which results in a break of the stacking sequence.
    • ii) Extrinsic stacking fault . An extra layer has been introduced between B and C layer. There are two breaks in the stacking sequence.
  • 32.  
  • 33. All About Metallurgical & Materials Engineering Download This & More Stuff @ WWW.07MET.TK

×