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Ch9 Vocab (Askeland)
Vocabulary Study Guide for MEE312
21
Mechanical Engineering
Undergraduate 3
03/06/2015

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Term
Chill Zone
Definition
a region of small randomly oriented grains that form at the surface/mold wall of a casting as the result of heterogeneous nucleation
Term
Columnar Zone
Definition
a region of elongated grains having a preferred orientation that forms as a result of competitive growth during solidification of a casting
Term
Critical Radius
Definition
the minimum size that must be formed by atoms clustering together in the liquid before the solid particle is stable and begins to grow
Term
Dendrite
Definition
the treelike structure of the solid that grows when an undercooled liquid solidifies
Term
Embryo
Definition
a tiny particle of solid that forms from the liquid as atoms cluster together, it may grow into a stable nucleus or redissolve
Term
Equiaxed Zone
Definition
a region of randomly oriented grains in the center of a casting produced as a result of widespread nucleation
Term
Grain Refinement
Definition
the addition of heterogeneous nuclei in a controlled manner to increase the number of grains in a casting
Term
Heterogeneous Nucleation
Definition
formation of critically sized from the liquid on an impurity surface
Term
Homogeneous Nucleation
Definition
formation of critically sized solid from the liquid by the clustering togehter of a large number of atoms at a high undercooling
Term
Innoculation
Definition
the addition of heterogeneous nuclei in a controlled manner to increase the number of grains in a casting
Term
Lamellar
Definition
a plate like arrangment of crystals within a material
Term
Latent Heat of Fusion
Definition
the heat evolved when a liquid solidifies, is related to the energy difference between the solid and the liquid
Term
Local Solidification Time
Definition
the time required for a particular location in a casting to solidify once nucleation has begun.
Term
Nucleation
Definition
the physical process by which a new phase is produced in a material, for solidification, the formation of a tiny stable solid
Term
Nuclei
Definition
tiny particles of solid that form from the liquid as atoms cluster together, because these particles are large enough to be stable, nucleation has occurred and growth of the solid can begin
Term
Planar Growth
Definition
growth of a smooth solid/liquid interface when no undercooling of the liquid is present
Term
Recalescence
Definition
the increase in temeprature of an undercooled liquid as a result of the liberation of latent heat of fusion
Term
Superheat
Definition
the pouring temperature minus the freezing temp
Term
Thermal Arrest
Definition
a plateau on the cooling curve during solidification of a material caused by the evolution of the latent heat of fusion during solidification
Term
Total Solidification Time
Definition
the time required for the casting to solidfy compeltely after the casting has been poured
Term
Undercooling
Definition
the temperature below which the liquid metal must cool below the equilibrium freezing temperature before nucleation can occur
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