Chapter 9 Definitions

Front 1

Argon oxygen decarburization (AOD)

Back 1

A process to refine stainless steel. The carbon dissolved in molten stainless steel is reduced by blowing argon gas mixed with oxygen.

Front 2

Brazing

Back 2

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.

Front 3

Cavities

Back 3

Small holes present in a casting.

Front 4

Cavity shrinkage

Back 4

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

Front 5

Chill zone

Back 5

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

Front 6

Chvorinov’s rule

Back 6

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

Front 7

Columnar zone

Back 7

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

Front 8

Continuous casting

Back 8

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

Front 9

Critical radius (r*)

Back 9

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

Front 10

Dendrite

Back 10

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

Front 11

Directional solidification (DS)

Back 11

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.

Front 12

Dispersion strengthening

Back 12

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.)

Front 13

Embryo

Back 13

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

Front 14

Epitaxial growth

Back 14

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

Front 15

Equiaxed zone

Back 15

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

Front 16

Fusion welding

Back 16

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

Front 17

Fusion zone

Back 17

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

Front 18

Gas flushing

Back 18

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.

Front 19

Gas porosity

Back 19

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.

Front 20

Glass-ceramics

Back 20

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

Front 21

Grain refinement

Back 21

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

Front 22

Growth

Back 22

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.

Front 23

Heterogeneous nucleation

Back 23

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

Front 24

Homogeneous nucleation

Back 24

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).

Front 25

Ingot

Back 25

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

Front 26

Ingot casting

Back 26

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

Front 27

Ingot structure

Back 27

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

Front 28

Inoculants

Back 28

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

Front 29

Inoculation

Back 29

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

Front 30

Interdendritic shrinkage

Back 30

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

Front 31

Investment casting

Back 31

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

Front 32

Lamellar

Back 32

A plate-like arrangement of crystals within a material.

Front 33

Latent heat of fusion (ΔHf)

Back 33

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

Front 34

Local solidification time

Back 34

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

Front 35

Lost foam process

Back 35

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

Front 36

Lost wax process

Back 36

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

Front 37

Microshrinkage

Back 37

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

Front 38

Mold constant (B)

Back 38

A characteristic constant in Chvorinov’s rule.

Front 39

Mushy-forming alloys

Back 39

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.

Front 40

Nucleation

Back 40

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.

Front 41

Nuclei

Back 41

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.

Front 42

Permanent mold casting

Back 42

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

Front 43

Photochromic glass

Back 43

Glass that changes color or tint upon exposure to sunlight.

Front 44

Pipe shrinkage

Back 44

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

Front 45

Planar growth

Back 45

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

Front 46

Preform

Back 46

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

Front 47

Pressure die casting

Back 47

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

Front 48

Primary processing

Back 48

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

Front 49

Rapid solidification processing

Back 49

Producing unique material structures by promoting unusually high cooling rates during solidification.

Front 50

Recalescence

Back 50

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

Front 51

Riser

Back 51

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.

Front 52

Sand casting

Back 52

A casting process using sand molds.

Front 53

Secondary dendrite arm spacing (SDAS)

Back 53

The distance between the centers of two adjacent secondary dendrite arms.

Front 54

Secondary processing

Back 54

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

Front 55

Shrinkage

Back 55

Contraction of a casting during solidification.

Front 56

Shrinkage porosity

Back 56

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

Front 57

Sievert’s law

Back 57

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.

Front 58

Skin-forming alloys

Back 58

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

Front 59

Soldering

Back 59

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

Front 60

Solidification front

Back 60

Interface between a solid and liquid.

Front 61

Solidification process

Back 61

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

Front 62

Solid-state phase transformation

Back 62

A change in phase that occurs in the solid state.

Front 63

Specific heat

Back 63

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

Front 64

Spherulites

Back 64

Spherical-shaped crystals produced when certain polymers solidify.

Front 65

Stainless steel

Back 65

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

Front 66

Superheat

Back 66

The difference between the pouring temperature and the freezing temperature.

Front 67

Thermal arrest

Back 67

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.

Front 68

Total solidification time

Back 68

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

Front 69

Undercooling

Back 69

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