Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001
I.Point Defects - crystal structure irregularities at a single point
1.Atom missing from crystal lattice
2.Lattice distortions around the vacancy
1.Extra atom squeezed into interstice of the lattice
2.Very rare in normal, densely packed structures
3.Extreme lattice distortions around the extra atom
C.Solid Solutions - alloys containing two or more different types of atoms
a.Small solute atoms in some of the interstices of the larger solvent atoms
b.Very dilute solutions due to large stresses involved
2.Substitutional Solid Solution
a.Atoms on solvent lattice replaced by solute atoms of a different type
b.Solubility limits dependent on
1.Atomic size - must be similar for large solubility
2.Crystal structure - greatest solubility if same lattice
3.Electronegativity - similar or intermetallic or ceramic may form
4.Valence - solute with same or higher valence than solvent for highest solubility
a.Atomic - fraction or % of atoms for each component present
b.Weight - fraction or % of the weight of each component
c.Conversions between wt. % and at. %
II.Linear Defects - crystal structure irregularities in one dimension
1.'Extra' half plane of atoms in crystal
2.Burger's Vector perpendicular to line of dislocation
3.Movement of dislocation leads to crystal offset equal to Burger's vector
1.Helical arrangement of atoms around the dislocation line
2.Burger's Vector parallel to line of dislocation
3.Movement of dislocation leads to crystal offset equal to Burger's vector
C.Mixed dislocation - most real dislocations in materials
1.Regions with edge, screw and mixed screw-edge character
2.Movement of dislocation leads to crystal offset equal to Burger's vector
III.Interfacial Defects - crystal structure irregularities in two dimensions
1.Atoms on surface have smaller coordination number than atoms in bulk
2.Coordination number - number of nearest neighbors
1.Region between individual crystals with less perfect bonding than in bulk of crystal
2.Lower coordination number - depends on degree of mismatch between crystals
1.Similar to a grain boundary but occurring within grains
2.Lattice on opposite sides of boundary are mirror images
IV.Bulk or Volume Defects - crystal structure irregularities in three dimensions - cracks, voids,
A.Polish surface of metal to mirror finish
B.Etch to preferentially erode atoms with lowest coordination number (weakest bonding)
C.Examine microscopically to see grain structure