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Cold work, recovery, recrystallization

Cold work, recovery, recrystallization. Example:Single crystal. State I:Annealed metal. Fairly strong and ductile. r  = 10 6 /cm 2. Low internal energy: stable. Cold worked. State II:Cold worked metal. r  = 10 10-12 /cm 2. Very strong and brittle. High internal energy: not very stable.

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Cold work, recovery, recrystallization

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  1. Cold work, recovery, recrystallization

  2. Example:Single crystal State I:Annealed metal Fairly strong and ductile r= 106/cm2 Low internal energy: stable

  3. Cold worked State II:Cold worked metal r= 1010-12/cm2 Very strong and brittle High internal energy: not very stable

  4. Heated at ~0.5 Tm State III:Recovered metal r= 108/cm2 Dislocation alignment: Polygonization (one recovery process) Strong and less brittle Compared to state II Internal energy is lowered

  5. Recall what a grain boundary is

  6. Heated at ~0.5 Tm State IV:Recrystallization begins r= 106/cm2 New strain free grains are formed by nucleation Stronger than state I and ductile Internal energy is further lowered

  7. Heated at ~0.5 Tm State V:Recrystallization complete r= 106/cm2 Recrystallized Stronger than state I and ductile

  8. In summary • We started with a single crystal and ended with a polycrystal : grain refinement • The driving force for this process is decrease in internal energy

  9. For a polycrystals ( in real life) Cold worked Initial recrystallization

  10. Recrystallized Grain growth

  11. Some facts • Without a minimum amount of cold work (5-15%), there is no recrystallization • After the metal is completely recrystallized, grain growth occurs • Grain growth law at a constant temperature Di2 - D02 = Kt Di = final grain size D0 = initial grain size t = time

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