Segregation

Definition - What does Segregation mean?

Segregation is the separation of materials. More specifically, it may refer to:

  • Material segregation - Enrichment of a material constituent at a free surface or an internal interface of a material

  • Particle segregation - Tendency of particulate solids to segregate by size, density, shape and other properties

In metallurgy, the process in which a component of an alloy or solid solution separates in small regions within the solid or on the solid's surface is called segregation.

Corrosionpedia explains Segregation

Segregation refers to non-uniformity of chemical composition. In cast products, segregation of solutes can occur upon freezing of alloys. The basic cause of segregation is that the liquid rejects solutes during freezing because the solid has less solubility as compared to the liquid.

In a polycrystalline solid, a segregation site can be:

  • Dislocation
  • Grain boundary
  • Stacking fault
  • Interface with a precipitate or secondary phase within the solid

Segregation of a solute to surfaces and grain boundaries in a solid produces a section of material with a discrete composition and its own set of properties that can have often deleterious effects on the overall properties of the material. For example, segregation at grain boundaries can lead to grain boundary fracture and affects sinterability as well as the grain boundary diffusivity.

Segregation of free surfaces also has important consequences involving the purity of metallurgical samples. Because of the favorable segregation of some impurities to the surface of the material, a very small concentration of impurity in the bulk of the sample can lead to a very significant coverage of the impurity on a cleaved surface of the sample. In an application where surface interactions are important, the result of segregation could be disastrous.

Segregation occurs because alloys, unlike pure metals, crystallize within a range of temperatures rather than at a certain fixed temperature. Segregation usually produces an adverse effect on the quality of metal, since it leads to irregularity of its properties. Intragranular corrosion is usually associated with chemical segregation effects or specific phases precipitated on the grain boundaries. Such precipitation can produce zones of reduced corrosion resistance in the immediate vicinity.

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