Chapter 9 Flashcards
Argon oxygen decarburization (AOD)
A process to refine stainless steel. The carbon dissolved
in molten stainless steel is reduced by blowing argon gas mixed with oxygen.
Brazing
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.
Cavities
Small holes present in a casting.
Cavity shrinkage
A large void within a casting caused by the volume contraction that occurs
during solidification
Chill zone
A region of small, randomly oriented grains that forms at the surface of a casting as a
result of heterogeneous nucleation.
Chvorinov’s rule
The solidification time of a casting is directly proportional to the square of the
volume-to-surface area ratio of the casting
Columnar zone
A region of elongated grains having a preferred orientation that forms as a result
of competitive growth during the solidification of a casting.
Continuous casting
A process to convert molten metal or an alloy into a semi-finished product
such as a slab.
Critical radius (r*)
The minimum size that must be formed by atoms clustering together in the
liquid before the solid particle is stable and begins to grow
Dendrite
The treelike structure of the solid that grows when an undercooled liquid solidifies
Directional solidification (DS
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.
Dispersion strengthening
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.)
Embryo
A particle of solid that forms from the liquid as atoms cluster together. The embryo may
grow into a stable nucleus or redissolve.
Epitaxial growth
Growth of a single-crystal thin film on a crystallographically matched singlecrystal
substrate.
Equiaxed zone
A region of randomly oriented grains in the center of a casting produced as a
result of widespread nucleation.
Fusion welding
Joining process in which a portion of the materials must melt in order to achieve
good bonding.
Fusion zone
The portion of a weld heated to produce all liquid during the welding process.
Solidification of the fusion zone provides joining
Gas flushing
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.
Gas porosity
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.
Glass-ceramics
Polycrystalline, ultra-fine grained ceramic materials obtained by controlled crystallization
of amorphous glasses.
Grain refinement
The addition of heterogeneous nuclei in a controlled manner to increase the
number of grains in a casting.
Growth
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.
Heterogeneous nucleation
Formation of critically-sized solid from the liquid on an impurity
surface.
Homogeneous nucleation
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).
Ingot
A simple casting that is usually remelted or reprocessed by another user to produce a more
useful shape.
Ingot casting
Solidification of molten metal in a mold of simple shape. The metal then requires
extensive plastic deformation to create a finished product.
Ingot structure
The macrostructure of a casting, including the chill zone, columnar zone, and
equiaxed zone.
Inoculants
Materials that provide heterogeneous nucleation sites during the solidification of a
material.
Inoculation
The addition of heterogeneous nuclei in a controlled manner to increase the number
of grains in a casting.
Interdendritic shrinkage
Small pores between the dendrite arms formed by the shrinkage that
accompanies solidification. Also known as microshrinkage or shrinkage porosity.
Investment casting
A casting process that is used for making complex shapes such as turbine
blades, also known as the lost wax process
Lamellar
A plate-like arrangement of crystals within a material
Latent heat of fusion ((delta)Hf)
The heat evolved when a liquid solidifies. The latent heat of fusion
is related to the energy difference between the solid and the liquid.
Local solidification time
The time required for a particular location in a casting to solidify once
nucleation has begun.
Lost foam process
A process in which a polymer foam is used as a pattern to produce a casting.
Lost wax process
A process in which a wax pattern is used to cast a metal
Microshrinkage
Small, frequently isolated pores between the dendrite arms formed by the shrinkage
that accompanies solidification. Also known as microshrinkage or shrinkage porosity
Mold constant (B)
A characteristic constant in Chvorinov’s rule.
Mushy-forming alloys
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.
Nucleation
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.
Nuclei
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.
Permanent mold casting
A casting process in which a mold can be used many times.
Photochromic glass
Glass that changes color or tint upon exposure to sunlight
Pipe shrinkage
A large conical-shaped void at the surface of a casting caused by the volume
contraction that occurs during solidification.
Planar growth
The growth of a smooth solid-liquid interface during solidification when no
undercooling of the liquid is present.
Preform
A component from which a fiber is drawn or a bottle is made.
Pressure die casting
A casting process in which molten metal is forced into a die under
pressure.
Primary processing
Process involving casting of molten metals into ingots or semi-finished useful
shapes such as slabs.
Rapid solidification processing
Producing unique material structures by promoting unusually
high cooling rates during solidification.
Recalescence
The increase in temperature of an undercooled liquid metal as a result of the liberation
of heat during nucleation.
Riser
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.
Sand casting
A casting process using sand molds
Secondary dendrite arm spacing (SDAS)
The distance between the centers of two adjacent
secondary dendrite arms.
Secondary processing
Processes such as rolling, extrusion, etc. used to process ingots or slabs
and other semi-finished shapes.
Shrinkage
Contraction of a casting during solidification.
Shrinkage porosity
Small pores between the dendrite arms formed by the shrinkage that accompanies
solidification. Also known as microshrinkage or interdendritic porosity.
Sievert’s law
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.
Skin-forming alloys
Alloys whose microstructure shows an outer skin of small grains in the chill
zone followed by dendrites.
Soldering
Soldering is a joining process in which the filler has a melting temperature below 450°C;
no melting of the base materials occurs
Solidification front
Interface between a solid and liquid
Solidification process
Processing of materials involving solidification (e.g., single crystal growth,
continuous casting, etc.).
Solid-state phase transformation
A change in phase that occurs in the solid state
Specific heat
The heat required to change the temperature of a unit weight of the material one degree
Spherulites
Spherical-shaped crystals produced when certain polymers solidify
Stainless steel
A corrosion resistant alloy made from Fe-Cr-Ni-C.
Superheat
The difference between the pouring temperature and the freezing temperature
Thermal arrest
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.
Total solidification time
The time required for the casting to solidify completely after the casting
has been poured.
Undercooling
The temperature to which the liquid metal must cool below the equilibrium freezing
temperature before nucleation occurs
Supercooling is considered (eutectic, eutectoid or peritectic))
eutectic, eutectoid)
superheating is(eutectic, eutectoid or peritectic))
peritectic
T / F Small supercooling - slow nucleation rate
True
T / F Small supercooling - many nuclei
False
T / F Small supercooling - large crystals
True
T / F Large supercooling - rapid nucleation rate
True
T / F Large supercooling - many nuclei
True
T / F Large supercooling - small crystals
True
Strain free grains nucleate a prior Cold Worked grain boundaries is known as
Recrystallization
Grain Size Strengthening takes Take advantage of heterogeneous or homogenous nucleation?
heterogeneous nucleation
__________ plays a critical role in the processing of
metals, alloys, thermoplastics and inorganic glasses
Solidification
______ produces a critical-size solid particle from
the liquid melt.
Nucleation
________ nucleation requires large undercooling
of the liquid and is not commonly observed.
Homogeneous
________ nucleation is always favored andallows a mechanism for generating fine grain sizes.
Heterogeneous
Control of the cooling process allows the generation
of desired internal _____ ________
grain structure
Do you know your cooling curves?
YES!
