Question 1

Cite 3 variables which determine the microstructure of an ALLOY

Accepted Answer

1) the alloying elements present, 

(2) the concentrations of these alloying elements, and 

(3) the heat treatment of the alloy.

Question 2

Isomorphous

Accepted Answer

Having the same crystal structures, and complete solid solubility for all compositions.

Question 3

Eutectic Structure

Accepted Answer

Two-phase  microstructure resulting from the solidification of a liquid having the eutectic comp,; phases exist as lamellae that alternate with each other.

Alternating layers of ALPHA and BETA.

Question 4

Phase

Accepted Answer

physically and chemically distinct regions that result from mixture; they must be homogeneous.

Question 5

Microconstituent

Accepted Answer

Element of the microstructure that has and identifiable and characteristic structure. It may consist of more than 1 phase (e.g., pearlite).

Question 6

Solubility Limit

Accepted Answer

The maximum conc. of solute that may be added w/o forming a new phase.

Question 7

Intermetallic Compound

Accepted Answer

A compound of 2 metals that has a distinct chemical formula. 

On a phase diagram, it appears as an intermediate phase that exists over a very narrow range of compositions.

They exist as a line on phase diagrams, not an area -- due to stoichiometry

Question 8

Tie Line

Accepted Answer

Horizontal line written across a 2 phase region of a binary phase diagram. It intersects with the phase boundaries at the equilibrium compositions of each phase at the given temperature (T).  Used to determine the concentrations of the two phases.

Question 9

Solid Solution

Accepted Answer

Homogeneous crystalline phase which contains 2 or more chemical species. 

Both substitutional and interstitial solid solutions are possible.

Question 10

What is the EUTECTIC reaction?

Accepted Answer

The EUTECTIC  reaction is where upon cooling, one solid phase transforms isothermally and reversibly into two new solid phases which are intimately mixed.

Question 11

What is PEARLITE?

Accepted Answer

A 2-phase microstructure found in some steels and cast irons.

Question 12

3 Rules of Phase Diagrams: If we know T & C_o, then we know what?

Accepted Answer

(1)The # & types of phases present,

(2)the composition of each phase, and 

(3) the amount of each phase.

Question 13

For a given temperature and composition of a binary alloy, can you identify the equilibrium compositions of each phase?

Accepted Answer

1. Construct tie line across two phase region
2. Note intersection values
3. Drop down perpendiculars from intersections to the horizontal comp. axis, which indicates the comp. of each phase

Question 14

For a given temperature and composition of a binary alloy, can you identify the equilibrium weight fractions of each phase? (LEVER Rule)

Accepted Answer

1. Construct tie line

2. fraction of one phase is computed by taking length of the OTHER phase and dividing by total tie line length

3. If phase percentages are desired, multiply each phase by 100. 
W_L=[C_a-C_o]/[C_a-C_L) & W_a=[C_o-C_L]/[C_a-C_L]

Question 15

What is the EUTECTOID reaction?

Accepted Answer

The EUTECTOID reaction is where one SOLID phase transforms, upon cooling, isothermally and reversibly into 2 NEW SOLID phases which are intimately mixed.

Question 16

Eutectic Temperature (T_E)

Accepted Answer

The LOWEST temp. at which there is a liquid present.  

Eutectic composition (C_E) is perpendicular to T_E line where it intersects lowest point of liquidus line.

Question 17

What does PEARLITE result from?

Accepted Answer

PEARLITE results from the transformation of austenite of EUTECTOID comp.

Question 18

What does PEARLITE consist of?

Accepted Answer

PEARLITE consists of alternating layers (or lamellae) of ALPHA-ferrite & cementite(e.g., Fe_3C).

Question 19

EUTECTOID Transformation = ?

Accepted Answer

SOLID <--> SOLID + SOLID (e.g. gamma (austenite) <--> alpha + Fe_3C)

Question 20

EUTECTIC Transformation = ?

Accepted Answer

Liquid <--> solid + solid (e.g., L <--> alpha + beta or L <--> gamma (austenite) + Fe_3C )

Question 21

PERITECTIC Transformation = ?

Accepted Answer

LIQUID & one SOLID phase transform to a 2ND SOLID Liquid + solid <--> Solid (e.g., S_1 + L <--> S_2

Question 22

For the Fe-C phase diagram, can you identify the eutectic and eutectoid points and describe the phase transformations that happen at them?

Accepted Answer

The EUTECTIC point occurs where the lowest temp. for possible liquids occurs (T_E). Thus, the transf. involves a LIQUID changing into 2 solids.

The EUTECTOID point is where 1 SOLID phase (austenite or gamma) transf. -> 2 NEW SOLID phases upon cooling

Question 23

For the Fe-C phase diagram, can you identify whether a certain composition will form proeutectoid (primary) ALPHA or proeutectoid (primary Fe_3C) cementite?

Accepted Answer

Proeutectiod (primary) ALPHA (-also pro-euctoid ferrite)is located b/t the ALPHA and GAMMA(austenite) regions. (i.e., it's LEFT of GAMMA region and below T_E)

Proeutectoid (primary Fe_3C) CEMENTITE is RIGHT of GAMMA region, and below T_E.

Question 24

How do you find the composition of PEARLITE in an Iron-Carbon (Fe_3C) alloy phase diagram?

Accepted Answer

Comp. PEARLITE = comp. of GAMMA (austenite)
(i.e., C_pearlite = C_y, should = 0.76 wt%C)

PROCEDURE: set tie line just above corresponding T_E of EUTECTOID

Question 25

What does ALLOYING to produce a solid solution usually do?

Accepted Answer

1. INCREASES the tensile strength (TS)

2. DECREASES the ductility

Question 26

Some binary alloys (alloys with two species) have only one solid phase such as a Copper and Nickel system.
Others have two solid phases such as a Lead and Tin system.

Why is this?

Accepted Answer

Cu and Ni have similar atomic radii, electronegativities, and
crystal structures, and so are mutually soluable.

Question 27

What is the difference between phase composition and phase fraction?

Accepted Answer

Composition refers to the chemical makeup of a phase (i.e., the composition of the alpha phase is 30 wt%Pb in Sn).

The phase fraction is the volume fraction of the material that is a given phase (i.e. the alloy is 30% liquid).

Ch.9: Phase Diagrams

Flashcards for hcapter 9 in MSE 2010 textbook

Question	Answer
Cite 3 variables which determine the microstructure of an ALLOY	1) the alloying elements present, (2) the concentrations of these alloying elements, and (3) the heat treatment of the alloy.
Isomorphous	Having the same crystal structures, and complete solid solubility for all compositions.
Eutectic Structure	Two-phase microstructure resulting from the solidification of a liquid having the eutectic comp,; phases exist as lamellae that alternate with each other. Alternating layers of ALPHA and BETA.
Phase	physically and chemically distinct regions that result from mixture; they must be homogeneous.
Microconstituent	Element of the microstructure that has and identifiable and characteristic structure. It may consist of more than 1 phase (e.g., pearlite).
Solubility Limit	The maximum conc. of solute that may be added w/o forming a new phase.
Eutectoid
Intermetallic Compound	A compound of 2 metals that has a distinct chemical formula. On a phase diagram, it appears as an intermediate phase that exists over a very narrow range of compositions. They exist as a line on phase diagrams, not an area -- due to stoichiometry
Tie Line	Horizontal line written across a 2 phase region of a binary phase diagram. It intersects with the phase boundaries at the equilibrium compositions of each phase at the given temperature (T). Used to determine the concentrations of the two phases.
Solid Solution	Homogeneous crystalline phase which contains 2 or more chemical species. Both substitutional and interstitial solid solutions are possible.
What is the EUTECTIC microconstituent and why does it form the way it does?
Why do some binary metal alloys have isomorphous phase diagrams?
What is the EUTECTIC reaction?	The EUTECTIC reaction is where upon cooling, one solid phase transforms isothermally and reversibly into two new solid phases which are intimately mixed.
What is true about the melting temperature of a EUTECTIC BINARY ALLOY at C_t?
What are FERRITE (alpha), AUSTENITE (gamma), and CEMENTITE phases?
What is PEARLITE?	A 2-phase microstructure found in some steels and cast irons.
What is the difference between FINE pearlite and COARSE pearlite in terms of the way they appear under a microscope?
3 Rules of Phase Diagrams: If we know T & C_o, then we know what?	(1)The # & types of phases present, (2)the composition of each phase, and (3) the amount of each phase.
For a given temperature and composition of a binary alloy, can you identify the equilibrium compositions of each phase?	1. Construct tie line across two phase region 2. Note intersection values 3. Drop down perpendiculars from intersections to the horizontal comp. axis, which indicates the comp. of each phase
For a given temperature and composition of a binary alloy, can you identify the equilibrium phases using the phase diagram?
For a given temperature and composition of a binary alloy, can you identify the equilibrium weight fractions of each phase? (LEVER Rule)	1. Construct tie line 2. fraction of one phase is computed by taking length of the OTHER phase and dividing by total tie line length 3. If phase percentages are desired, multiply each phase by 100. W_L=[C_a-C_o]/[C_a-C_L) & W_a=[C_o-C_L]/[C_a-C_L]
What is the EUTECTOID reaction?	The EUTECTOID reaction is where one SOLID phase transforms, upon cooling, isothermally and reversibly into 2 NEW SOLID phases which are intimately mixed.
Eutectic Temperature (T_E)	The LOWEST temp. at which there is a liquid present. Eutectic composition (C_E) is perpendicular to T_E line where it intersects lowest point of liquidus line.
What does PEARLITE result from?	PEARLITE results from the transformation of austenite of EUTECTOID comp.
What does PEARLITE consist of?	PEARLITE consists of alternating layers (or lamellae) of ALPHA-ferrite & cementite(e.g., Fe_3C).
EUTECTOID Transformation = ?	SOLID <--> SOLID + SOLID (e.g. gamma (austenite) <--> alpha + Fe_3C)
EUTECTIC Transformation = ?	Liquid <--> solid + solid (e.g., L <--> alpha + beta or L <--> gamma (austenite) + Fe_3C )
PERITECTIC Transformation = ?	LIQUID & one SOLID phase transform to a 2ND SOLID Liquid + solid <--> Solid (e.g., S_1 + L <--> S_2
For the Fe-C phase diagram, can you identify the eutectic and eutectoid points and describe the phase transformations that happen at them?	The EUTECTIC point occurs where the lowest temp. for possible liquids occurs (T_E). Thus, the transf. involves a LIQUID changing into 2 solids. The EUTECTOID point is where 1 SOLID phase (austenite or gamma) transf. -> 2 NEW SOLID phases upon cooling
For the Fe-C phase diagram, can you identify whether a certain composition will form proeutectoid (primary) ALPHA or proeutectoid (primary Fe_3C) cementite?	Proeutectiod (primary) ALPHA (-also pro-euctoid ferrite)is located b/t the ALPHA and GAMMA(austenite) regions. (i.e., it's LEFT of GAMMA region and below T_E) Proeutectoid (primary Fe_3C) CEMENTITE is RIGHT of GAMMA region, and below T_E.
How do you find the composition of PEARLITE in an Iron-Carbon (Fe_3C) alloy phase diagram?	Comp. PEARLITE = comp. of GAMMA (austenite) (i.e., C_pearlite = C_y, should = 0.76 wt%C) PROCEDURE: set tie line just above corresponding T_E of EUTECTOID
What does ALLOYING to produce a solid solution usually do?	1. INCREASES the tensile strength (TS) 2. DECREASES the ductility
What is the difference between a phase and a microconstituent?
What is the phenomenon of coring and why does it occur? What is one undesirable effect of coring?
Some binary alloys (alloys with two species) have only one solid phase such as a Copper and Nickel system. Others have two solid phases such as a Lead and Tin system. Why is this?	Cu and Ni have similar atomic radii, electronegativities, and crystal structures, and so are mutually soluable.
What is the difference between phase composition and phase fraction?	Composition refers to the chemical makeup of a phase (i.e., the composition of the alpha phase is 30 wt%Pb in Sn). The phase fraction is the volume fraction of the material that is a given phase (i.e. the alloy is 30% liquid).

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