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Dislocations + GB/Interfaces

Dislocations + GB/Interfaces. Stress at heterointerfaces can be relieved by dislocations Other dislocations interact with GBs & Interfaces In general, these are barriers Classic Hall-Petch effect. Boundaries as Barriers. GB+dislocation Dislocations in GB interact with dislocation

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Dislocations + GB/Interfaces

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  1. Dislocations + GB/Interfaces • Stress at heterointerfaces can be relieved by dislocations • Other dislocations interact with GBs & Interfaces • In general, these are barriers • Classic Hall-Petch effect

  2. Boundaries as Barriers • GB+dislocation • Dislocations in GB interact with dislocation • Attractive or repulsive, does not matter • Dislocation traversing GB creates jogs/kinks in GB dislocations (energy) • New dislocation at GB (b=bout-bin) • Charge effects as well • GBs can be charged, also dislocations

  3. Effective Superdislocation Hirth & Lothe, 21-2

  4. Dislocation Density

  5. Hall-Petch Effect • Pileup effectively increases the stress on the leading dislocation • Maximum stress scales as 1/L1/2 • Hence, as grain size decreases more external stress is needed

  6. Dislocation Pileup

  7. Dislocation Pileup

  8. Grain Boundary Barrier 1

  9. Grain Boundary Barrier 2

  10. Al Indentation ExperimentsNucleation at surfaces Courtesy Oden Warren (Hysitron) & Andy Minor (NCEM)

  11. Summary • Different types of GBs/Interfaces • Note the similarities • Low Angle • CSL • Low Index Faces • Co-incidence of Reciprocal Lattice

  12. Summary, continued • FK/FVdM • Simpler harmonic + periodic model • Captures most of the important aspects • Strain localization • Dissociation of dislocations • Model is imperfect, nowadays atomistic models used • Note: atomistic models are as good (or bad), they have their own approximations

  13. Some Properties • Enhanced Diffusion • Separate Phase (Thermodynamic) • Barriers to most things (not all) • Current, dislocations etc • Classic Hall-Petch effect • Source of dislocations (as are surfaces)

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