Polymorphism - more than one crystal structure in a chemical compound
Allotropy - more than one crystal structure in a chemical element.
Single crystal - periodic arrangement of atoms - no grain boundaries!!!!
Polycrystalline - several crystals having different crystal orientations.
Grain boundary - atomic mismatch
non-crystalline - amorphous, no system arrangement of atoms (liquid).
Anistropy - directionality in properties!!!
Isotropy - having the same properties in all directions
Dislocation - linear or non-linear defect.
Edge dislocation - is a linear defect that centers on the line that is defined along the end of the extra
half-plane of atoms
screw dislocation - spiral planar ramp resulting from shear deformation
Mixed dislocation - A dislocation that is neither screw or edge
Burgers vector - magnitude and direction of the lattice distortion assosicated with a dislocation (perp,
edge. Parallel, screw. neither mixed)
, Interfacial Defects - boundaries that have two dimensions and normally separate regions of the
materials that have different crystal structures and/or crystallographic orientations
External surfaces - surface area depends on the packing planar density.
Grain boundaries - tilt boundary (aligned angle of misorientation) and twist
boundary (parallel angle); light mismatch between grains.
Phase boundaries - a different phase exists on each side of the boundary
Twin boundaries - a special type of grain boundary across which there is a specific mirror lattice
symmetry
Stacking faults - occur when there is an error in the planar stacking sequence
as the packing density increases, the surface
Energy.... - decreases
Volume defects - extended defects (pores, cracks)
Diffusion - Material transport by atomic motion
Interdiffusion/impurity diffusion - atoms of one metal diffuse into another
Self-diffusion - - all atoms exchanging positions are of the same type (no
composition available) - vacancy mechanisms only.
For the diffusion mechanism the following conditions must be met: - --> Must be empty adjacent site.
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