Chapter 9 Phase Diagram

Question 1

What are alloys ?

Answer 1

Alloys are mixture of elements depending on the mixture everything can change properties such as mechanical electrical and chemical.

Question 2

What does dissolution of element depends on ?

Answer 2

Concentration and temperature.

Question 3

What is liquid solution ?

Answer 3

Mixing of two things solute ( ingredients added to the matrix they are interstitial and substitutional . Solvent is the matrix solutes are added too.

Question 4

What is solid solution ?

Answer 4

Mixing of solids ( via chemical reactions) I.e diffusion

Question 5

What is given by
solubility limit?

Answer 5

Amount of solute that can be dissolved in a solvent is given by the solubility limit. This depends on the of the temperature and concentration.

Question 6

What is it resulting graph of concentration and temperature called?

Answer 6

Phase diagram

Question 7

What does solubility defines ?

Answer 7

Solubility defines the region where phase exist.

Question 8

What is difference between phases ?

Answer 8

So phases are different based on their chemistry and or / physical arrangement in the mixture.

Question 9

What can be seen on phase diagram ?

Answer 9

Solid solution: alpha beta ( lower case )
Solidus line. Below this temp, the material is solid . Liquid line above this temp material is liquid

Question 10

What can we get out of phase diagram ?

Answer 10

A phase diagram is a graphical representation that shows the relationship between the phases of a substance (solid, liquid, gas) at different temperatures and pressures. Here are some key insights you can gain from a phase diagram:

1. Phase Regions: It clearly delineates the regions where different phases exist, helping to identify whether a substance is solid, liquid, or gas under specific conditions.
2. Phase Transitions: You can identify the conditions under which phase transitions occur, such as melting, boiling, or sublimation, and see how these transitions depend on temperature and pressure.
3. Triple Point: The point where three phases coexist can be observed, providing crucial information about the unique conditions under which all three phases are stable.
4. Critical Point: This indicates the end of the liquid-gas phase boundary, beyond which the substance exhibits properties of both phases, helping to understand phenomena like supercritical fluids.
5. Clarity on Stability: Phase diagrams show which phase is thermodynamically stable under certain conditions, aiding in the study of material properties and behaviors.
6. Compositions: In multi-component systems, phase diagrams can show how different compositions affect phase behavior, useful in alloy design and chemical reactions.
7. Temperature and Pressure Dependence: They highlight how changes in temperature and pressure can influence the stability and existence of different phases.

Overall, phase diagrams are invaluable in fields like chemistry, materials science, geology, and engineering for understanding material behavior and guiding experimental design.

Question 11

Describe the process of the (1) “which phase are present at which temperature and pressure combination.

Answer 11

Phase present (easiest) locate the material asked in the question then read the weight percent then read the temperature than match the common point.

Question 12

Describe the process for combination of phase.

Answer 12

1) find the temp of interest
2) draw a horizontal line
3) read off where the line intersects

Question 13

list the step for
The weight fraction of each phase.

Answer 13

1) construct the line at given temperature and given concentration
2) The overall ally composition is located on the tie-line
3) identify the regions (segments) corresponding to the 2 phase the weight fraction is calculated

“opposite line”/”total tie-line”

Question 14

Is liquid a primary phase ?

Answer 14

No liquid is not a primary state.

Question 15

what happens to liquid at the eutectic point?

Answer 15

At the eutectic point, a liquid is transformed directly into solid mixture of two distinct solids

Question 16

what is the temp at which liquid is directly transformed into a solid mixture called ?

Answer 16

The temp at which rxn takes place is called the “eutectic isotherm “.

Question 17

What are the phases forming above and below the eutectic isotherm called?

Answer 17

Any phase forming above the eutectic isotherm are called primary (pro-eutectic). Below the eutectic temp the phases are called total.

Question 18

What is the structure of alpha and beta phase ?

Answer 18

They have a FCC structure.

Question 19

Solubility in each of these solid phases is limited in that in temperature below only a limited concentration of silver dissolve in copper for alpha phase and same for copper in silver beta phase.(T/F)

Answer 19

True

Question 20

What does solivus line sperate?

Answer 20

it sperates alpha and alpha+beta phase

Question 21

what does solidus line sperate ?

Answer 21

it separates solid and liquid+solid phase

Question 22

what does liquidus sperate?

Answer 22

it separates liquid and sloid+liquid phase

Question 23

What does line BEG mean (i.e line the staright line where isotherm is)

Answer 23

the horizontal line BEG may also be considered a solidus line. It represent the lowest temperature at which liquid phase may exist.

Question 24

at what point are all the phases in equilbirum in eutectic binary diagram ?

Answer 24

at eutectic point

Question 25

at what composition does eutectic rection happens?

Answer 25

At eutectic composition

Question 26

what is hypoeutectic ?

Answer 26

These alloys have a composition less than the eutectic composition (to the left of the eutectic point on the phase diagram)

Question 27

what is hypereutectic ?

Answer 27

These alloys have a composition greater than the eutectic composition (to the right of the eutectic point on the phase diagram)

Question 28

Describe the transition of pure iron as it is heated?

Answer 28

1) it starts off with alpha ferrite which is BCC
2) at 912C converts to austenite (FCC)
3) at 1394 C converts to delta ferrite which is BCC
4) 1538 C converts to liquid

Question 29

Can we have austenite at room temperature ?

Answer 29

No austenite cannot exist at room temperature

Question 30

At what concentartion does pure iron exist Fe-C diagram?

Answer 30

0-0.002 wt % C

Question 31

At what concentartion does STEEL exist Fe-C diagram?

Answer 31

0.008 wt % C-2.14 wt % C

Question 32

At what concentartion does cast iron exist exist Fe-C diagram?

Answer 32

2.14-6.7 wt% C

Question 33

what is compostion greater than 6.7 wt % C?

Answer 33

For compostion greater than 6.7 wt % Fe and C combine to transform a phase called cementite

Question 34

The amount of C that dissolve in Fe depends on the crystal structure of Fe (T/F)

Answer 34

True

Question 35

The amount of C that dissolve in C depends on the crystal structure of Fe. Describe for alpha ferrite ?

Answer 35

Alpha ferrite is bcc has only few interestial position. Which means we cannot dissolve too much in it. The ,aximum is 0.0022 wt % C

Question 36

The amount of C that dissolve in C depends on the crystal structure of Fe. Describe for austenite?

Answer 36

The spacing in FCC structure is greater than BCC. Therefore, we can dissolve more carbon max is 2.14 wt % C ( the spacing is 100 times bigger in FCC than BCC)

Question 37

where does eutectic reaction take place in Fe-C ?

Answer 37

at 4.3 wt % C

Question 38

where does eutectoid reaction take place in Fe-C?

Answer 38

at 0.76 wt % C

Question 39

what is difference between eutectic and eutectoid ?

Answer 39

Eutectic: transformation of liquid phase into two distinct solid phase
Eutectoid: transformation of solid phase into two distinct solid phase

Question 40

what is pearlite ?

Answer 40

The combination of alpha+Fe-C is called pearlite. Pearlite microstructure is observed at room temperature.

Question 41

what is composition of eutectoid and temperature at which transformation occur?

Answer 41

Eutectoid composition is 0.76 wt % C and temp where transformation occur is 727 C degree. Above 727 phase that is present is austenite and below 727 austenite transforms into two distinct solid ferrite (alpha) and Fe-C (cementite)

Question 42

Describe HYPO-eutectoid ?

Answer 42

-Hypo-eutectoid is between 0.022-0.76 wt % C
-alloy start with austenite but this temperature doesnt exist at room temperature.
-As the temperature is decreased we entre two phase region of ferrite + austenite.
-Therefore in HYPO ferrite is pro-eutectoid or “primary”.
-Austenite weight fraction will decrease until it is fully disappeared at 727
-at the eutectoid temp alpha that is form is called EUTCTOID FERRITE
-the remening austenite transfer into pearlite
final structure is pro-eutectoid ferrite + pearlite.

Question 43

At the eutectoid temp alpha that is form is called EUTCTOID FERRITE (T/F)

Answer 43

T

Question 44

What is HYPEREUTECTOID

Answer 44

-it is between 0.76-2.14 wt %
-the material starts with austenite
-when entre two phase region ‘‘austenite + Fe-C” the cementite will precipitate on grain boundaries
-Cementite Fe-C is proeutectoid/ primary in this case
-austenite disappear after 727 fully transitioning to pearlite
-final structure proeutectoid cementite+pearlite
-

Question 45

depending on which state is present on the grain boundary the strenght/mechanical response of the alloy will be fundamentally different (T/F)

Answer 45

T