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Unformatted text preview: Chapter 6 Diffusion Introduction Diffusion = the phenomenon of material transport by atomic motion Interdiffusion = Impurity Diffusion = diffusion of atoms of one metal into another metal Self-diffusion = atomic migration in pure metals Diffusion Mechanisms For atoms to make such a move, two conditions must be met o There must be an empty adjacent site o The atom must have sufficient energy to break bonds with its neighbor atoms and then cause some lattice distortion during the displacement Vacancy Diffusion = mechanism involving the interchange of an atom from a normal lattice position to an adjacent vacant lattice site or vacancy Interstitial Diffusion = diffusion that involves atoms that migrate from a interstitial position to a neighboring one that is empty o In metal occurs faster than vacancy because interstitial atoms are smaller Steady-State Diffusion Rate of mass transfer, J= M/(At) o M=mass, A=area, t=time o Units: kg/m 2-s or atoms/m 2-s Steady-state diffusion = when diffusion flux does not vary with time...
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This note was uploaded on 01/02/2012 for the course ENME enme382 taught by Professor Bruck during the Spring '10 term at Maryland.
- Spring '10