Diffusion
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Diffusion is material transport by atomic motion.
It can take place between S-S, S-L, S-G.
Conditions for an atom to diffuse
othere must be an empty adjacent site
othe atom must have sufficient energy to break bonds with its neighbour
atoms an
Solids
The interior angles of the polygons
meeting at a vertex of a polyhedron
add to less than 360 degrees.
1
Platonic Solids
3 triangles at a vertex
Octahedron
4 triangles at a vertex
Icosahedron
5 triangles at a vertex
Cube
3 squares at a vertex
Dodeca
Phase Transformations
Kinetics of Phase Transformation
Avrami Equation
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Rate of a transformation is taken as the reciprocal of
time
required for the transformation to proceed halfway to completion
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Metastable vs Equilibrium State
Stable
Un
Failure of Metals
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Ductile
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Moderately ductile
Brittle
Stages in
Initial necking
small cavity formation
Cup and
Cone fracture
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Crack propagation
fracture
Final shear
coalescence of cavi
to form crack
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Spherical Dimples
Di
Imperfections in solids
1
Why are imperfections important?
Crystal
Structure
+
Bonding
+
Imperfections
Examples:
Secondary processing of metals
Doping in Si
Formation of alloy
Propertie
s
Outline
o Point Defects
o Linear Defects
o Interfacial Defects
o Bu
Fundamentals of
structure of crystalline
solids
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Crystallography
Crystallography is the experimental science of the
arrangement of atoms in solids.
2
Solids
The interior angles of the polygons
meeting at a vertex of a polyhedron
add to less than 360 degr