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[Fizinfo] DE Szilardtest Fizika Tanszek, Szeminarium

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  • From: ERDELYI Zoltan <zerdelyi AT>
  • To: fizinfo AT
  • Subject: [Fizinfo] DE Szilardtest Fizika Tanszek, Szeminarium
  • Date: Tue, 21 Feb 2012 16:42:41 +0100
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  • List-id: ELFT HÍRADÓ <>

* Debreceni Egyetem, Szilárdtest Fizika Tanszék *
* *

Időpont: 2012. február 24., péntek, 11:00 óra

Helyszín: Szilárdtest Fizika Tanszék, Előadó terem
-------- Debrecen, Bem tér 18/b.

------- Reactive diffusion and stresses in spherical geometry


Debreceni Egyetem
Szilárdtest Fizika Tanszék

We have developed a complete set of analytical equations to describe reactive diffusion in spherical core shell nanostructures. [Acta Mater 2012,60:2817] The model takes into account elastic stress, its plastic relaxation, as well as possible non-equilibrium vacancy densities. Furthermore, thermodynamic driving forces are included to model formation of intermetallic product phases in intermediate composition range. The complex model can be considered as Stephenson’s model [[Acta Metal 1988;36:2663] on spherical geometry. Using our derivation, however, even the original equations for the planar case may be deduced in an easier way than in the original work by Stephenson.

We apply the model to the reaction in spherical triple layers A/B/A and B/A/B, for which Schmitz et al. [Acta Mater 2009;57:2673] observed by atom probe tomography that growth rate depends on the stacking order. The inhomogeneous stress field induces an inhomogeneous distribution of vacancies. The resulting vacancy gradient provides an additional driving force that hinders the outward flux of vacancies. As a consequence, diffusion of the faster component towards the center can only proceed by slow Nernst–Planck interdiffusion instead of conventional fast Darken transport.

The model calculations provide evidence that the experimentally observed growth asymmetry can only appear if vacancy sinks and sources are present at the incoherent interphase boundaries but not within the formed intermetallic product layer.

The developed model will presumably also be useful in clarifying the role of stress in today’s popular core shell nanostructures.


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