Phase diagrams Complete solid Solubility Flashcards
What is a phase?
A phase can be a state (like solid, liquid or gas) but also refer to different crystal structures (like FCC, BCC and HCP).
So we can have different phases in alloys (from differing crystal structures).
What is a phase diagram?
It is a temperature compositie map. It shows what phases exist under ideal and equilibrium conditions for a given composite and temperature.
Temperature is often shown on the y-axis, while the x-axis shows composition.
What is the solubility limit, often shown as a line?
A line that defines the amount of one element you can get into another. Solubility limit increases with temperature, but up to a point mostly. Past that line you get solids in the liquids as no more of one element can be dissolved into another.
What are the types of solid solubility a material can have?
- Complete solid solubility: one solid phase forms across the whole composition range.
- Partial (or no) solid solubility: two solid phases exist (dependent on the composition) with distinct and different crystal structures
- There can also be the formation of intermalecular compounds: where additional phases form, such as incoherent precipitates.
What does the liquidous line represent?
Above the liquidious line, the composition is completely in the liquid state. Below that line solidification starts to occur.
What does the solidus line represent?
Above the line, the composition of the elements are either slightly solidified or liquid. Below the line, the composition of the material is completely solid.
How do you use tie-lines to find the compositions of a liquid and solid phase of a material?
Tie-lines are a hozirontal line between the liquidious and solidus line.
To find the liquid composition percentage:
* Go to the point where the tie-line hits the liquidous line and read off the value on the x-axis where this occurs.
To find the solid composition percentage:
* Go to the point where the tie-line hits the solidus line and read off the value on the x-axis where this occurs.
How do you use the Lever rule to find the fraction of a material that is either solid or liquid in phase?
To find the fraction of a phase:
* amount of phase = opposite length / overall length
What happens to an alloy as you cool from a liquid phase to a solid phase, under ideal and equilibrium conditions?
This is more refering to composition percent
The solids composition will reduce as more of the material solidifies.
The liquids composition percent will also decrease as the amount of liquid material reduces.
What is the microstructure fomation like under equilibrium cooling?
As the alloy cools, we get some solid forming in the liquid. As further cooling, atoms pack into a specific structure: dendritic-type structure. These grow until we hit the solid line and then we have grains.
What is the microstructure formation like under non-equilibrium cooling?
In reality if cooling is too fast coring occurs. We get regions with different compositions in the solids growing and forming. We get higher percentage compositions in the middle and lower out.
