lecture21 - Diffusion in Homogeneous Concentrated Alloys In...

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Diffusion in Homogeneous Concentrated Alloys In a homogeneous concentrated alloy, two tracer diffusion coefficients can be defined, one for each species: AB A D * AB B D * and They can be measured through a thin-film experiments using tracer atoms. By varying the composition of the homogeneous alloy, the dependencies of the tracer diffusion coefficients on the alloy composition can be measured. A B x B A A D * B A D * A B D * B B D * Diffusion Along Extended Defects (Chapter 6 in Shewmon) (a) Cavities (b) Precipitates (c) Surfaces (d) Grain Boundaries Diffusion in a system with extended defects is determined by two effects: (1) the jump frequency difference in the bulk and along the extended defects, (2) segregation or depletion of diffusing species to extended defects. In general, L d Q Q < L d D D >> L dis gb sur D D D D > > >
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A Simple Microscopic Picture i Γ i Γ o Γ o Γ ' Γ ' Γ Γ Grain boundary o i Γ > Γ Segregation of diffusion species onto the grain boundary Γ > Γ ' Short-circuiting diffusion along the
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lecture21 - Diffusion in Homogeneous Concentrated Alloys In...

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