Ch 8

Question 1

Define equilibrium

Answer 1

Changes are carried out slowly enough that the phases in the system have the same properties everywhere and there are no concentration gradients

Question 2

Is diffusion faster, slow in solids

Answer 2

Slow

Question 3

Define phase

Answer 3

A region of matter which has homogeneous physical and chemical properties

Question 4

Define phase diagram

Answer 4

A graphical representation (map) of the phases present with variations in temperature in composition, when thermodynamic equilibrium has been achieved

Question 5

Define polyphase materials

Answer 5

Materials containing two or more coexisting phases

Question 6

4 things that the properties of polyphase materials depend on

Answer 6

Question 7

Define components

Answer 7

The elements (atoms), molecules, or compounds, which are initially mixed

Question 8

Define solute

Answer 8

Present in minor concentration

Question 9

Define solvent

Answer 9

Present in major concentration

Question 10

Define solubility limits

Answer 10

The max concentration of solute that may be added, without forming a new phase

Question 11

Define metastable

Answer 11

Nonequilibrium state, which may persist for a very long time

Question 12

Are metastable phases, shown on phase diagrams

How can they be formed?

Answer 12

No

Can be formed due to rapid cooling

Question 13

Define isomorphous

Answer 13

Having the same structure

Question 14

What does isomorphous mean in terms of phase diagrams?

Answer 14

Isomorphicity is having the same crystal structure in the solid phase and complete solid solubility for all compositions

Question 15

Binary phase diagrams: what happens when a mixture exhibit clustering in the solid

Answer 15

A miscibility gap

Question 16

What does a binary phase diagram show?

Answer 16

The phases present at equilibrium of two different elements

Question 17

Describe the binary phase diagram

(Where liquid and solids are and the liquidus line and solidus line)

Answer 17

Question 18

Define solidus line

(2 definitions)

Answer 18

Line on the phase diagram, where solidification is complete upon equilibrium cooling

Where melting begins upon heating

Question 19

In heating what’s line must you stay below?

Answer 19

Solidus line

Or it will lose its shape by partial melting

Question 20

Define liquidus line

(2 definitions)

Answer 20

Line on a phase diagram above, which melting of a solid is complete upon heating

Where solidification begins upon cooling

Question 21

In melting an alloy what do you need to do if you want a homogeneous liquid

Answer 21

Must exceed the liquidus line

Question 22

Define system composition/overall composition

Answer 22

How much of each element is present in total?

Question 23

What variable represents system composition?

Answer 23

Question 24

Define Tieline

Answer 24

A horizontal line constructed across a two phase region of binary phase diagrams 

Question 25

What does the tie line intersect on either end?

Answer 25

The phase boundaries that represent the equilibrium composition at the given temperature in the question

Question 26

Steels: what are the two Greek letter symbols for the solid phases

Answer 26

Question 27

Define phase constitution (3 things)

Answer 27

The number and types of phase is present The composition of each phase The amount of each phase

Question 28

Describe the three things you get from a tie line

Answer 28



Question 29

What does the evolution of the microstructure depend on?

Answer 29

How rapidly the system is cooled

Question 30

Can you see microstructure under a microscope?

Answer 30

Yes

Question 31

Three things that micro structure includes

Answer 31

Phase constitution Morphology and spatial distribution of phases

Question 32

What does the evolution of the microstructure depend on?

Answer 32

How rapidly the system has cooled from high temperature

Question 33

Phase diagrams: as a liquid solution is cooled it will start solidifying at what line

Answer 33

Liquidus line

Question 34

Phase diagrams: what leads to concentration gradients in grains

Answer 34

The change in concentration with decreasing temperature if cooling is rapid

Question 35

Phase diagrams: what happens if we cool slowly enough

Answer 35

The grains at formal experience diffusion in the concentration gradient, due to compositional changes during cooling will be illuminated

Question 36

Phase diagrams: at true equilibrium what can be said about the composition and structure of each phase

Answer 36

They are spatially uniform

Question 37

Phase diagrams: why is the composition of the solid and liquid phase is changing as a system is cooled

Answer 37

Because the liquidus and solidus lines have a slope to them

Question 38

Define eutectic

Answer 38

Easily melted

Question 39

Eutectic phase diagrams: define invariant point

Answer 39

Where there is an equilibrium between the two phase solid region, and a liquid

Question 40

Eutectic phase diagrams: what happens upon heating?

Answer 40

Liquid starts to format the eutectic temperature

Question 41

What variable represents eutectic temperature?

Answer 41

Question 42

What type of phase diagram is this?

Answer 42

Binary eutectic phase diagram

Question 43

Label the six different lines

Answer 43

Question 44

What do the blue arrow show?

Answer 44

The max solid solubility for the single phase solids These compositions are the endpoints of the eutectic isotherm

Question 45

What is the most common eutectic structure?

Answer 45

Lamellar eutectic

Question 46

What are the hypo and hyper eutectic compositions based on? (Binary eutectic, phase diagrams)

Answer 46

Based on the component on the left side, being the solvent in the component on the right side, being the solute

Question 47

Define hypo, eutectic composition

Answer 47

Are the range of compositions above the solubility limit of being a at the eutectic temperature up to, but less than the eutectic composition

Question 48

In terms of hypo and hyper, which one means less, and which one means more

Answer 48

Hypo equals less Hyper equals more

Question 49

Define hypereutectic composition

Answer 49

The range of compositions above the eutectic composition up to the solid solubility limit of ANB at the eutectic temperature

Question 50

Define the pro eutectic phase

Answer 50

The first phase to start solidifying from the liquid upon cooling for a hypo or hyper eutectic overall composition

Question 51

What is the notation for pro eutectic? (And other name)

Answer 51

Primary phase

Question 52

At what temperature does the protective phase form?

Answer 52

Add temperatures above the eutectic temperature, but below the liquidus

Question 53

Binary, eutectic diagram: where is the hypo eutectic Eutectic Hypereutectic

Answer 53

Question 54

A eutectoid reaction is similar to a eutectic reaction, except for what

Answer 54

The high temperature liquid phase replaced by another solid phase so that the whole reaction is in solid state

Question 55

Define eutectoid reaction

Answer 55

Upon cooling one solid phase, transforms, isothermal, he and reversibly into two new solid faces that are intimately mixed

Question 56

Define eutectic reaction

Answer 56

Upon cooling a liquid phase transforms, isothermal, he and reversibly into two intimately mixed solid faces

Question 57

Defined the proeutectoid phase (primary phase)

Answer 57

A solid that starts to nuclear at a service line rather than at the liquidus line