08-12-2012, 02:25 PM
MATERIALS ENGINEERING AND TECHNOLOGY
[attachment=43063]
Volume, planar and Linear density calculations
Volume density = mass per unit cell/ volume per unit cell Planer atomic density = equ. no of atoms having centres in the selected plane of intersect/ selected area Linear atomic density = no of atoms dia intersected by the selected line in the direction/ selected length of line
Atomic packing Factor (APF) = volume of atoms in a unit cell/ total unit cell volume
Co-ordination number
In unit cells made by similar atoms, coordination number is defined as number of other atoms which are in contact with a specified atom. Primitive Unit cell The co-ordination number in simple cubic (Primitive) unit cell. BCC In body centred unit cell, the co-ordination number is 8, atom present at body centre touches all the corner atoms. FCC Co-ordination number of any atom in fcc or ccp unit cell is 12
Screw Dislocation
For an edge dislocation the Burgers vector is orthogonal to the
dislocation line.
For a screw dislocation, the Burgers vector is parallel to the dislocation line.
• The elastic strain energy associated with the dislocation is
proportional to the square of the Burgers vector.
• For metallic materials, the Burgers vector for a dislocation will point in a closed-packed crystallographic direction and will be of magnitude equal to the inter-atomic spacing.
[attachment=43063]
Volume, planar and Linear density calculations
Volume density = mass per unit cell/ volume per unit cell Planer atomic density = equ. no of atoms having centres in the selected plane of intersect/ selected area Linear atomic density = no of atoms dia intersected by the selected line in the direction/ selected length of line
Atomic packing Factor (APF) = volume of atoms in a unit cell/ total unit cell volume
Co-ordination number
In unit cells made by similar atoms, coordination number is defined as number of other atoms which are in contact with a specified atom. Primitive Unit cell The co-ordination number in simple cubic (Primitive) unit cell. BCC In body centred unit cell, the co-ordination number is 8, atom present at body centre touches all the corner atoms. FCC Co-ordination number of any atom in fcc or ccp unit cell is 12
Screw Dislocation
For an edge dislocation the Burgers vector is orthogonal to the
dislocation line.
For a screw dislocation, the Burgers vector is parallel to the dislocation line.
• The elastic strain energy associated with the dislocation is
proportional to the square of the Burgers vector.
• For metallic materials, the Burgers vector for a dislocation will point in a closed-packed crystallographic direction and will be of magnitude equal to the inter-atomic spacing.