Recrystallization Theoretical & Practical Aspects - Materials Science ...

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Intro <strong>Recrystallization</strong> Lab 1 Grain Boundaries Nucleation Issues • Nucleation in recrystallization must be a heterogeneous nucleation process because the driving force is too small to sustain homogeneous nucleation. • Estimate of driving force, E: – Energy per unit length of dislocation ≈ Gb 2 – Thus energy/volume, E ≈ Gb 2 ρ – Typical cold worked dislocation density, ρ = 10 15 .m -2 – For Al, G = 27GPa, b =0.28nm,E ≈ 2 J.m -3 ( = 2MPa) – For a boundary energy σ = 0.5 J.m -2 , the critical nucleus size, r crit = 2σ/Ε 2 ≈ 0.25µm, which is a very large (too large!) critical radius. • Therefore nucleation in recrystallization must be heterogeneous. 18
Intro <strong>Recrystallization</strong> Lab 1 Grain Boundaries Heterogeneous Nucleation • Nucleation of recrystallization therefore occurs on defects in the material. • Sites for nucleation: – Prior grain boundaries (strain induced boundary migration, SIBM) – Deformation bands or shear bands, i.e. regions of nonuniform rotation of the lattice – Coarsening (recovery) of a subgrain structure – Coarsening (recovery) of dislocation structure near to coarse particles; this is called Particle Stimulated Nucleation (PSN). 19
Page 1 and 2: Intro Recrystallization Lab 1 Grain
Page 9 and 10: Grain size as a function of prior d
Page 13 and 14: Intro Recrystallization Lab 1 Tempe
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Recrystallization Theoretical & Practical Aspects - Materials Science ...

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