Lecture 8 - Crystal Structue 4 Flashcards
What is screw dislocation
Motion through a crystal
When a plane of atoms are displaced by one step
Dislocation is along a line
Plane of atoms are connected to ones beside there correct position
How can screw dislocations be moved
By bonds breaking and reforming
What is mixed dislocation and what do sit produce
Appears on one face like screw dislocations and on the perpendicular face as edge dislocation.
Produces a curved line defect through the structure
How do crystals form
Deposition from a liquid or gas onto another surface
More efficient way to arrive near an atom
Start at the nuclei ( they have random initial orientation)
As more atoms are deposited the atoms grow from the initial nuclei
What happens when most atoms solidify when crystals form
You get gaps between the crystals of different initial nuclei. This creates grains. Grains meet at boundaries
Where do you get atomic plane misalignment
At grain boundaries
How can you define the degree of misalignment when crystals are forming
Small or low angle grain boundary
High angle grain boundary
What type of boundary does an edge dislocation have
Tilt boundary
What type of grain boundary does a screw dislocation have
Twist - high angle boundary
What does grain boundaries control
Crol yield and deformation behaviour
How do you measure lattices
X-ray diffraction
What are x-rays
Electromagnetic waves of very short wavelength
What happens when x rays get into the structure of the materials
Deflected by the atoms of the materials
What is energy proportional to (E)
Frequency (v)
What is energy inversely proportional to (E)
Wavelength
