GRAIN REFINEMENT

'Grain refinement' is a set of techniques used in metallurgy to ensure that the crystallites (''grains'') that make up a metallic object are sufficiently small, so as to increase its strength. The gained strength is caused by the increase of grain boundaries surfaces in the same volume, which act as obstacles for the movement of dislocations. Dislocation propagation is impeded because of the stress field of the grain boundary defect region and the lack of slip planes and slip directions and overall alignment across the boundaries
One common technique is to induce a very small fraction of the melt to solidify at a much higher temperature than the rest; this will generate seed crystals that act as a template when the rest of the material falls to its (lower) melting temperature and begins to solidify. Since a huge number of minuscule seed crystals are present, a nearly equal number of crystallites result, and the size of any one grain is limited.
An - intermetallic with a very high melting temperature serves this role in most titanium alloys.
TiB2 is a common grain refiner for Al alloys; however, novel refiners such as Al3Sc have been suggested.

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See also

See also

★ supercooling