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Micrograph of a polycrystalline metal; grain boundaries evidenced by acid etching. Differently-oriented crystallites in a polycrystalline material. In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material.
Figure 1: Hall–Petch strengthening is limited by the size of dislocations. Once the grain size reaches about 10 nanometres (3.9 × 10 −7 in), grain boundaries start to slide. In materials science, grain-boundary strengthening (or Hall–Petch strengthening) is a method of strengthening materials by changing their average crystallite (grain
This is also known as intercrystalline fracture or grain-boundary separation. More rapid diffusion along grain boundaries than along grain interiors; Faster nucleation and growth of precipitates at the grain boundaries; Quench cracking, or crack growth following a quenching process, is another example of intergranular fracture and almost always ...
Intergranular corrosion is generally considered to be caused by the segregation of impurities at the grain boundaries or by enrichment or depletion of one of the alloying elements in the grain boundary areas. Thus in certain aluminium alloys, small amounts of iron have been shown to segregate in the grain boundaries and cause intergranular ...
Grain translations and rotations: [1] in crystalline rock, sliding along grain boundaries can be induced from deviatoric stresses, resulting grain boundary cracks. [1] In clastic rock, the grains may be rotated by neighbor grains, forming cracks in the cement or along the grain boundary.
Grain boundaries disrupt the motion of dislocations through a material, so reducing crystallite size is a common way to improve strength, as described by the Hall–Petch relationship. Since grain boundaries are defects in the crystal structure they tend to decrease the electrical and thermal conductivity of the material.
Another possible mechanism for producing mechanical weakness is grain boundary sliding, where grains slide slightly past each other under stress, lubricated by the traces of volatiles present. [10] Weakening below oceanic plates is partly caused by their motion itself, thanks to the non-linear dislocation creep mechanism. [23]
This sort of partitioning of solute atoms between the grain boundary and the lattice was predicted by McLean in 1957. [3] Non-equilibrium segregation, first theorized by Westbrook in 1964, [4] occurs as a result of solutes coupling to vacancies which are moving to grain boundary sources or sinks during quenching or application of stress. It can ...