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Materials Science > Chapter 9 (Phase diagrams) > Flashcards

Chapter 9 (Phase diagrams) Flashcards

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1
Q

What are the components?

A

the elements or compounds which are mixed initially

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2
Q

what are the phases?

A

the physically and chemically distinct material regions

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3
Q

what is the solubility limit?

A

maximum amount of solute that can go into solution in solvent. Also the maximum concentration for which a single phase can occur

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4
Q

what happens after the solubility limit is exceeded?

A

we have now created a 2 phase mixture

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5
Q

what is equilibrium

A

the state of lowest free energy, also the most stable one

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6
Q

what is particular about equilibrium phase diagrams

A

there are no rapid changes in state

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7
Q

what is a binary alloy?

A

a mixture of 2 metals

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8
Q

what is a ternary alloy?

A

a mixture of 3 metals

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9
Q

what characteristics should 2 metals have to become an alloy? (4)

A
  1. Both FCC
  2. similar size
  3. similar valence
  4. they should be good solubility
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10
Q

how do we determine the composition of a mixture of phases from a phase diagram?

A

from the point we draw a line across to each phse a down from those points to the x-axis, those values will give us the respective compositions

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11
Q

describe how to use the tie line?

A

the numerator will always be the distance AWAY from the phase youre trying to determine

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12
Q

what is the liquidus line

A

the line ABOVE which ONLY LIQUID is present

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13
Q

what is the solidus line

A

the line BELOW which ONLY SOLID is present

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14
Q

what can be said about solid state diffusion

A

takes more time and temperature

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15
Q

what can be said about the grain structure during equilibrium cooling

A

the grains would be uniform

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16
Q

what would happen if the material was cooled very quickly?

A

the final grain composition would not be uniform, aka “CORED” grains

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17
Q

what are cored grains

A

when we cool a materials very quickly, the inner layer has a different composition from the outer layer

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18
Q

what is a eutectic reaction?

A

when a liquid is transformed into 2 different solid phases

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19
Q

how many phases are there at the eutectic line?

A

3

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20
Q

how are fixed compositions represented?

A

by vertical lines on phase diagrams

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21
Q

what is eutectic?

A

a liquid in equilibrium with two solids (L alpha + Beta)

22
Q

what is eutectoid

A

solid phase in equilibrium with 2 other solids phases

a –» Beta+gamma

23
Q

what is peritectic

A

liquid+solid 1 —> solid 2

24
Q

in the Iron carbon system what is alpha?

A

ferrite. an interstitial solid solution of carbon in BCC iron

25
Q

in the Iron carbon system what is gamma?

A

austenite, an interstitial solid solution of carbon in FCC iron

26
Q

in the Iron carbon system what is Fe3C

A

cementite

27
Q

in the Iron carbon system what is delta

A

ferrite, an interstitial solid solution of carbon in BCC iron

28
Q

what is the eutectic temperature in the iron carbon phase diagram?

A

1147 C

29
Q

what is the eutectoid temperature in the iron carbon phase diagram

A

727 C

30
Q

what type of steel is less than 0.76 weight percent

A

HYPO-eutectoid

31
Q

what type of steel is 0.76 wt% C

A

eutectoid steel

32
Q

what type of steel is >0.76 wt% C

A

HYPER-eutectoid

33
Q

what is pearlite and in what type of reaction is this formed

A

alpha + Fe3C, Eutectoid reaction

34
Q

how can we increase the solubility limit

A

by increasing the temperature

35
Q

what do equilbrium diagram basically show us

A

what phases are present at equilibrium

36
Q

what has to be the case for solid state diffusion to take place

A

it requires a lot of time and temperature, so we must cool it very slowly to allow diffusion to take place

37
Q

what can be said about the percent composition of phase if we cool a solid with non-equilibrium cooling

A

we know there must be a greater percentage of liquid than for equilibrium cooling

38
Q

what process can we use to remove coring

A

homogenization

39
Q

True of false, the eutectic composition freezes at a higher temperature than other composition

A

false, lower

40
Q

how can we describe the grain diagram at the eutectic temperature

A

alternating layers of alpha and beta crystals (hatched bars)

41
Q

if there is more of the L+alpha phase than the L+beta phase when the eutectic temperature is reached, then will it be hypo or hyper eutetectic

A

hypo

42
Q

which type of structure are favored eutectic reactions

A

ones that have higher interfacial areas, eg: lamellar, rod-like, globular. They aren’t usually equiaxed grains

43
Q

graphically, what is the effect of solid solution strengthening on tensile strength and ductility respectively

A

upward parabola for tensile strength, and downward parabola for ductility

44
Q

List the number of single phase regions and 2-phase regions in Binary Eutectic phase diagrams

A

single phase: 3

2-phase: 3

45
Q

what are the solid solutions at the sides of the phase diagram called?

A

Terminal Phases

46
Q

How do intermetallic compounds appear on phase diagrams?

A

AS VERTICAL LINES

47
Q

Furthermore, what can be said about intermetallic compounds in terms of their composition?

A

they have FIXED composition

48
Q

what is the peritectic temperature?

A

1493 deg C

49
Q

true of false, eutectoid reactions don’t involve liquids

A

true

50
Q

name the 2 important points for the IRON-CARBON phase diagram

A
  1. Eutectic: L -» gamma +Fe3C
    @1147 deg C
  2. Eutectoid: gamma -» alpha +Fe3C
    @ 727 deg C
51
Q

which structure is the easiest for Pearlite?

A

Lamellar structure

52
Q

if we add other elements to the Fe-Fe3C diagram what can happen?

A
  • eutectoid temp can move up or down

- eutectoid can move to higher or lower carbon concentrations

Materials Science (13 decks)

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