Materials 2 Flashcards
How to translate the design requirements into properties and constraints?
- Function?
- Constraints.
- Objectives.
- Free variables.
FCC
Face- centred cubic.
{111} are close packed.
<110> directions are close packed.
HCP
Hexagonal Close Packed.
{0001} planes are close packed.
<1120} directions are close packed.
Is most brittle as it has only 3 or 6 slip systems.
BCC
Body centred cubic.
No close packed planes.
<111> directions are close packed.
So, has it has no close packed planes, it is less ductile.
Define a slip system
The set of symmetrically identical slip planes (and associated family of slip directions) for which dislocation motion can easily occur and lead to plastic deformation.
Define polymorphism.
Any material that can exist in more than one form or structures.
What are the types of solid solutions?
Substitutional solid solution.
Interstitial solid solution.
Explain the types of substitutional solid substitution.
- Random
- Ordered (where B atoms prefer A atoms)
- Clustered (where B atoms prefer B atoms)
How much solute can we dissolve?
If you add too much solute, you may exceed the solubility limit and the solute will precipitate as a new solution.
This could be 2 random solutions (where nothing has an order at all)
or perhaps 1 ordered and 1 random.
Define a phase
A region of material with uniform physical and chemical properties. Phases have their own grains.
Define a grain-boundary
A grain is a region with the same crystal orientation, but has an eenrgy associated with them.
Define phase boundary
For 2-phase materials, these have an energy associated with them to join them together.
Boundaries in metals.
- Coherent (has the least energy)
- Coherency-strain
- Semi-coherent (has gaps)
- Incoherent (has the most energy)
Interfacial energy
E = GB * A
Grain boundary energy * interfacial area.
If the GB is isotropic, then the lowest E is for the shape with the lowest interfacial area.
For isotropic shapes, what is the best interfacial area? in two phase materials?
A sphere.
Because the grains want to grow in the direction of the lowest energy - and mathematically, the best shape in this case is a sphere.
For non-isotropic shapes, what is the best interfacial area? in two phase materials?
A plate. - it has the lowest gb energy.
What happens if the E(gb) = E(ab)
The beta can form their own grains adjacent to the alpha grains. This is the shape that minimises energy.
Define an alloy
The result of taking a pure metal and
adding other elements (Or “mixture of
elements”)
Define an Alloy System
All the alloys that can be made from the
components
Define a component
The elements that make up an alloy.
Define a composition
Usually measured in weight % (mass%)
Define constitution
A combination of:
The overall composition (e.g. Al-4Cu)
The number of phases present
The composition of each phase
The percentage by weight of each phase
What does the alloy constitution base on?
The number of phases present
The volume fraction of phases
The composition of each phase
These depend on:
- overall composition
- temperature.
What happens about the liquidus line
All is liquid.