Describe the differences between recovery, recrystallization, and grain growth during heat treatment of metals.

Recovery is the first stage of  annealing process On the one hand, with  higher temperature relief occurs  internal efforts caused by work in  cold, (residual stresses), and on the other hand,  microstructural changes occurs

Recrystallization: If a previously cold deformed metal,  is annealed at a temperature  high enough, (temperature of  recrystallization), new crystals appear  in the microstructure, those that have identical  composition and reticular structure that  old undeformed grains

Grain growth, this  occurs when annealing is continued then  if recrystallization is completed

Explanation:

When a metal is plastically deformed  temperatures well below that of its  melting point, it is said that the metal has been  cold worked Most of the  energy used in this deformation is  dissipates as heat, storing a  small fraction as energy of  deformation. The latter is accumulated in  form of dislocations and defects  punctual, for example: broken links and  vacancies As the density increase of  dislocation is not even, zones occur  of higher density, which leads to  cell generation

Recovery

Comprises a series of  phenomena that occur at more temperatures  very low, with respect to the temperature of  fusion of the material, among which you can  highlight:

 Annihilation of specific defects

 Polygonization

 Drop in electrical resistivity (R)

The annihilation of specific defects  consists of diffusion, by adding  of heat, from vacancies to  dislocations and grain borders, so  manages to decrease its quantity to the number  equilibrium at temperature  correspondent.

Recrystallization

The driving force of recrystallization  comes from the stored energy of  cold work .

Recrystallization temperature  corresponds to the approximate temperature of  which a highly cold worked material  it completely recrystallizes in one hour. Recrystallization is sensitive to changes in  the temperature at which it is performed, rather than at  time to temperature variations  constant.

Grain growth

A process aimed at eliminating surface energy in grain boundaries. This process implies a greater chemical stability since the total energy stored in the material is reduced. If the structure of the grain limits is uniform and the energy of the limits is isotropic, then it has to do with the reduction of the grain limit area. The process is activated by adding heat to the material