Materials Lecture 8 Partial Solubility.

Question 1

A phase diagram is a perfect world diagram. Assumes perfect conditions. Tells us how the phase of a mixture varies with temperature and composition.

Question 2

What is partial and Complete Solid Solubility?

Answer 2

Complete solid solubility: When the Solute can diffuse into the solvent crystal lattice structure and only one solid phase is present across the whole composition range (even as composition goes from 0 to 100% solute atoms the crystal lattice structure (solid phase) remains the same.)

Partial solubility: Where up to a certain composition only one solid phase (crystal structure exists) and then two different crystal structures (solid phases) exist in the material. Can also have no solubility where the solute atoms cannot diffuse into the solvent lattice no matter the conditions. Two solids phases cannot mix no matter the conditions.

Question 3

Practice reading Phase diagrams with multiple solubility lines. Lecture 8 Slide 5.

Question 4

What does Eutectic mean?

Answer 4

A Eutectic reaction is where a liquid phase turns into two different solid phases. Each solid phase has different compositions of the atoms of the two solids and/or a different crystal structure.

Question 5

What makes two solids phases different?

Answer 5

If the two phases have different compositions of the atoms of each element present and/ or a different crystal structure.

Question 6

At the eutectic temperature what occurs (going down)?

Answer 6

A lamellar structure of the two solid phases is formed. The two solid phases have different compositions so there are different numbers of each type of atom in each solid phase. Therefore diffusion needs to occur and the fastest/ lowest energy structure for this to occur is the lamellar structure. A lamellar structure is alternating lines of the two solid phases. The two solid phases formed within the lamellar structure are called eutectic ‘alpha’ and eutectic ‘beta’. They have the same composition and crystal structure as a primary alpha and beta but are in a lamellar structure and so are formed via a eutectic reaction.

Summary:
Lamellar structure of eutectic alpha and eutectic beta are formed. Reason fro eutectic structure is structure which allows faster diffusion/ diffusion which requires the least amount of energy.

Question 7

What is hypoeutectic and hypereutectic?

Answer 7

Hypoeutectic is when the eutectic line is reached to the left of the eutectic point (point at which liquidus line touches eutectic line.) This means that (if alpha forms on the left of the phase diagram) that there will be primary alpha and eutectic alpha and eutectic beta. There is always an equal amount of eutectic alpha and eutectic beta forming no matter where on the eutectic line you are however due to the primary alpha also present there is overall an uneve composition of alpha and beta. More alpha in this case.

Hypereutectic is the same thing however for beta at any point on the right of the eutectic point (since we chose alpha on the left and beta on the right.) Amounts of eutectic alpha and eutectic beta remain the same within the eutectic structure always however since there is also primary beta there is overall more beta in the material.

Question 8

What is the meaning of primary when applied to solid phases? (e.g. alpha and beta solid phases)

Answer 8

Primary means that the solid phase was present before the eutectic temperature was reached. This ‘primary’ has a dendrite crystal structure within the liquid it is in. So when the eutectic temperature is reached and eutectic alpha and beta form the primary alpha was there before this and has a dendrite structure rather than a eutectic lamellar structure.

Question 9

When you have a solid phase and you cross a line (not sure the name of this line) and you go from alpha solid phase to alpha and beta solid phase what is occurring?

Answer 9

The beta phase is formed from the solute atoms forming a new solid phase. This occurs at the grain boundaries because the solute atoms can come together using the least amount of energy at the grain boundaries. Diffusion occurs more easily at the grain boundaries due to the high energy area there so the new beta solid phase forms most easily at these grain boundaries. So the Beta phase starts growing from the grain boundaries.

Question 10

See slide 10 to double check using lever rule for phase diagrams finding primary alpha amount when there are multiple solubility lines.

Answer 10

Amount of primary alpha in alpha + liquid = distance of tie-line from eutectic temp up to our chosen composition / distance from eutectic point to end of alpha + liquid solid phase meeting the eutectic line.

Question 11

If you look at a material at composition C2 at 100 degrees will you see a eutectic alpha and beta structure or alpha with beta at the grain boundaries? Or is the lamellar structure and the beta growing at the alpha grain boundaries the same thing? Slide 1 Lecture 8.

Question 12

What is an inter metallic compound?

Question 13

How do you define/find the liquidus and solidus lines?

Answer 13

Solidus line is where melting of the solid phase begins to produce an increasing amount of liquid as the temperature increases.

Double check if this is where the two eutectic slid phases start to melt or it can only be just one solid phase melting.

Question 14

What am I essentially researching/learning here?

Answer 14

The microstructures that form and how they form as alloys solidify.

Question 15

In a binary system?

Answer 15

Alloy made of two elements the three phases can only coexist at a single point (the eutectic point, two different solid phases within the eutectic structure and the liquid phase) and single phase fields are always separated by a two-phase field.