Recovery (metallurgy)

Under crystal recovery is defined as the elimination of the consequences of plastic deformation (eg cold forming) without formation of the microstructure ( recrystallization). Crystal relaxation leads to the reduction of tensions. Grain shape and grain size of the deformed structure are preserved. By raising the temperature, the crystal recovery is favored due to larger atomic mobility. For aluminum occurs a noticeable crystal recovery after cold working at room temperature one, with steel, this is hardly the case.

The crystal recovery is primarily due to two effects occurring in parallel, the healing and the rearrangement of zero - and one-dimensional lattice defects.

The healing of zero-dimensional error occurs by diffusion of interstitial atoms in lattice vacancies. One-dimensional error, so edge and screw dislocations, healing through mutual annihilation sign of other dislocations. In the zero-dimensional rearrangement error to vacancies or interstitials stored in the lattice half-planes of the dislocations, so that the edge dislocations can change their position - they climb. By climbing of stairs and cross slip of screw dislocations can rearrange in an energetically more favorable position, arrange them in regular rows and form so-called small-angle grain boundaries. This Polygonisationsvorgang arise within a crystallite sub-grains with a very low dislocation density in their interior and dislocation- rich, web-like structures on their borders.

Materials show after the crystal recovery a higher ductility. With increasing temperature, recovery operations are increasingly favored in the microstructure. This is reflected in the mechanical properties, for example, by a decrease of hardness and tensile strength down. If temperature and / or degree of deformation increased further, relying in particular on metals with low stacking fault energy increasingly recrystallization processes, coupled with a complete structure formation, a.

Find the rest even during the transformation takes place, it is called dynamic recovery - in all other cases of static recovery.

• Materials Science
• Solid State Chemistry