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Materials > Chapter 9 > Flashcards

Chapter 9 Flashcards

1
Q

Argon oxygen decarburization (AOD)

A

A process to refine stainless steel. The carbon dissolved

in molten stainless steel is reduced by blowing argon gas mixed with oxygen.

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2
Q

Brazing

A

An alloy, known as a filler, is used to join two materials to one another. The composition of
the filler, which has a melting temperature above 450°C, is quite different from the metal being joined.

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3
Q

Cavities

A

Small holes present in a casting.

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4
Q

Cavity shrinkage

A

A large void within a casting caused by the volume contraction that occurs
during solidification

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5
Q

Chill zone

A

A region of small, randomly oriented grains that forms at the surface of a casting as a
result of heterogeneous nucleation.

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6
Q

Chvorinov’s rule

A

The solidification time of a casting is directly proportional to the square of the
volume-to-surface area ratio of the casting

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7
Q

Columnar zone

A

A region of elongated grains having a preferred orientation that forms as a result
of competitive growth during the solidification of a casting.

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8
Q

Continuous casting

A

A process to convert molten metal or an alloy into a semi-finished product
such as a slab.

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9
Q

Critical radius (r*)

A

The minimum size that must be formed by atoms clustering together in the
liquid before the solid particle is stable and begins to grow

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10
Q

Dendrite

A

The treelike structure of the solid that grows when an undercooled liquid solidifies

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11
Q

Directional solidification (DS

A

A solidification technique in which cooling in a given direction
leads to preferential growth of grains in the opposite direction, leading to an anisotropic and an oriented
microstructure.

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12
Q

Dispersion strengthening

A

Increase in strength of a metallic material by generating resistance
to dislocation motion by the introduction of small clusters of a second material. (Also called second-
phase strengthening.)

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13
Q

Embryo

A

A particle of solid that forms from the liquid as atoms cluster together. The embryo may
grow into a stable nucleus or redissolve.

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14
Q

Epitaxial growth

A

Growth of a single-crystal thin film on a crystallographically matched singlecrystal
substrate.

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15
Q

Equiaxed zone

A

A region of randomly oriented grains in the center of a casting produced as a
result of widespread nucleation.

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16
Q

Fusion welding

A

Joining process in which a portion of the materials must melt in order to achieve
good bonding.

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17
Q

Fusion zone

A

The portion of a weld heated to produce all liquid during the welding process.
Solidification of the fusion zone provides joining

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18
Q

Gas flushing

A

A process in which a stream of gas is injected into a molten metal in order to eliminate
a dissolved gas that might produce porosity.

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19
Q

Gas porosity

A

Bubbles of gas trapped within a casting during solidification, caused by the lower
solubility of the gas in the solid compared with that in the liquid.

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20
Q

Glass-ceramics

A

Polycrystalline, ultra-fine grained ceramic materials obtained by controlled crystallization
of amorphous glasses.

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21
Q

Grain refinement

A

The addition of heterogeneous nuclei in a controlled manner to increase the
number of grains in a casting.

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22
Q

Growth

A

The physical process by which a new phase increases in size. In the case of solidification,
this refers to the formation of a stable solid as the liquid freezes.

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23
Q

Heterogeneous nucleation

A

Formation of critically-sized solid from the liquid on an impurity
surface.

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24
Q

Homogeneous nucleation

A

Formation of critically sized solid from the liquid by the clustering
together of a large number of atoms at a high undercooling (without an external interface).

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25
Q

Ingot

A

A simple casting that is usually remelted or reprocessed by another user to produce a more
useful shape.

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26
Q

Ingot casting

A

Solidification of molten metal in a mold of simple shape. The metal then requires
extensive plastic deformation to create a finished product.

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27
Q

Ingot structure

A

The macrostructure of a casting, including the chill zone, columnar zone, and
equiaxed zone.

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28
Q

Inoculants

A

Materials that provide heterogeneous nucleation sites during the solidification of a
material.

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29
Q

Inoculation

A

The addition of heterogeneous nuclei in a controlled manner to increase the number
of grains in a casting.

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30
Q

Interdendritic shrinkage

A

Small pores between the dendrite arms formed by the shrinkage that
accompanies solidification. Also known as microshrinkage or shrinkage porosity.

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31
Q

Investment casting

A

A casting process that is used for making complex shapes such as turbine
blades, also known as the lost wax process

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32
Q

Lamellar

A

A plate-like arrangement of crystals within a material

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33
Q

Latent heat of fusion ((delta)Hf)

A

The heat evolved when a liquid solidifies. The latent heat of fusion
is related to the energy difference between the solid and the liquid.

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34
Q

Local solidification time

A

The time required for a particular location in a casting to solidify once
nucleation has begun.

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35
Q

Lost foam process

A

A process in which a polymer foam is used as a pattern to produce a casting.

36
Q

Lost wax process

A

A process in which a wax pattern is used to cast a metal

37
Q

Microshrinkage

A

Small, frequently isolated pores between the dendrite arms formed by the shrinkage
that accompanies solidification. Also known as microshrinkage or shrinkage porosity

38
Q

Mold constant (B)

A

A characteristic constant in Chvorinov’s rule.

39
Q

Mushy-forming alloys

A

Alloys with a cast macrostructure consisting predominantly of equiaxed
grains. They are known as such since the cast material seems like a mush of solid grains floating in
a liquid melt.

40
Q

Nucleation

A

The physical process by which a new phase is produced in a material. In the case of
solidification, this refers to the formation of small, stable solid particles in the liquid.

41
Q

Nuclei

A

Small particles of solid that form from the liquid as atoms cluster together. Because
these particles are large enough to be stable, growth of the solid can begin.

42
Q

Permanent mold casting

A

A casting process in which a mold can be used many times.

43
Q

Photochromic glass

A

Glass that changes color or tint upon exposure to sunlight

44
Q

Pipe shrinkage

A

A large conical-shaped void at the surface of a casting caused by the volume
contraction that occurs during solidification.

45
Q

Planar growth

A

The growth of a smooth solid-liquid interface during solidification when no
undercooling of the liquid is present.

46
Q

Preform

A

A component from which a fiber is drawn or a bottle is made.

47
Q

Pressure die casting

A

A casting process in which molten metal is forced into a die under
pressure.

48
Q

Primary processing

A

Process involving casting of molten metals into ingots or semi-finished useful
shapes such as slabs.

49
Q

Rapid solidification processing

A

Producing unique material structures by promoting unusually

high cooling rates during solidification.

50
Q

Recalescence

A

The increase in temperature of an undercooled liquid metal as a result of the liberation
of heat during nucleation.

51
Q

Riser

A

An extra reservoir of liquid metal connected to a casting. If the riser freezes after the casting,
the riser can provide liquid metal to compensate for shrinkage.

52
Q

Sand casting

A

A casting process using sand molds

53
Q

Secondary dendrite arm spacing (SDAS)

A

The distance between the centers of two adjacent

secondary dendrite arms.

54
Q

Secondary processing

A

Processes such as rolling, extrusion, etc. used to process ingots or slabs
and other semi-finished shapes.

55
Q

Shrinkage

A

Contraction of a casting during solidification.

56
Q

Shrinkage porosity

A

Small pores between the dendrite arms formed by the shrinkage that accompanies
solidification. Also known as microshrinkage or interdendritic porosity.

57
Q

Sievert’s law

A

The amount of a gas that dissolves in a metal is proportional to the square root of
the partial pressure of the gas in the surroundings.

58
Q

Skin-forming alloys

A

Alloys whose microstructure shows an outer skin of small grains in the chill
zone followed by dendrites.

59
Q

Soldering

A

Soldering is a joining process in which the filler has a melting temperature below 450°C;
no melting of the base materials occurs

60
Q

Solidification front

A

Interface between a solid and liquid

61
Q

Solidification process

A

Processing of materials involving solidification (e.g., single crystal growth,
continuous casting, etc.).

62
Q

Solid-state phase transformation

A

A change in phase that occurs in the solid state

63
Q

Specific heat

A

The heat required to change the temperature of a unit weight of the material one degree

64
Q

Spherulites

A

Spherical-shaped crystals produced when certain polymers solidify

65
Q

Stainless steel

A

A corrosion resistant alloy made from Fe-Cr-Ni-C.

66
Q

Superheat

A

The difference between the pouring temperature and the freezing temperature

67
Q

Thermal arrest

A

A plateau on the cooling curve during the solidification of a material caused by
the evolution of the latent heat of fusion during solidification. This heat generation balances the heat
being lost as a result of cooling.

68
Q

Total solidification time

A

The time required for the casting to solidify completely after the casting
has been poured.

69
Q

Undercooling

A

The temperature to which the liquid metal must cool below the equilibrium freezing
temperature before nucleation occurs

70
Q

Supercooling is considered (eutectic, eutectoid or peritectic))

A

eutectic, eutectoid)

71
Q

superheating is(eutectic, eutectoid or peritectic))

A

peritectic

72
Q

T / F Small supercooling - slow nucleation rate

A

True

73
Q

T / F Small supercooling - many nuclei

A

False

74
Q

T / F Small supercooling - large crystals

A

True

75
Q

T / F Large supercooling - rapid nucleation rate

A

True

76
Q

T / F Large supercooling - many nuclei

A

True

77
Q

T / F Large supercooling - small crystals

A

True

78
Q

Strain free grains nucleate a prior Cold Worked grain boundaries is known as

A

Recrystallization

79
Q

Grain Size Strengthening takes Take advantage of heterogeneous or homogenous nucleation?

A

heterogeneous nucleation

80
Q

__________ plays a critical role in the processing of

metals, alloys, thermoplastics and inorganic glasses

A

Solidification

81
Q

______ produces a critical-size solid particle from

the liquid melt.

A

Nucleation

82
Q

________ nucleation requires large undercooling

of the liquid and is not commonly observed.

A

Homogeneous

83
Q

________ nucleation is always favored andallows a mechanism for generating fine grain sizes.

A

Heterogeneous

84
Q

Control of the cooling process allows the generation

of desired internal _____ ________

A

grain structure

85
Q

Do you know your cooling curves?

A

YES!

Materials (8 decks)

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