activity energy of Mn in GB

ripening phenomena, dislocations, grainboundary topology
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Ls_Thu
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activity energy of Mn in GB

Post by Ls_Thu » Wed Jul 07, 2021 4:50 pm

Dear Bernd,

Thank you so much for your previous kind help and they are quit helpful !

And there is a new problem for the activity energy for the boundary-duffusion.

Please check the text in attachment. We want to study the effect of the activity energy of Mn in grain boundary. We think at 720C the austenite transformation is controlled by Mn-diffusion (certified by experiments) . And we changed 'the Correction for activation energy' for Mn (see below 2 files). but the growth rate for both are the same.

We are confused why it is.

This subject is one of the parts for a work, thus we don't wish to change another parameters or as less as we can.

Regards,

Sai
Attachments
low act energy.txt
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high act energy.txt
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Bernd
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Re: activity energy of Mn in GB

Post by Bernd » Thu Jul 08, 2021 5:43 pm

Dear Sai,


Please note that the "mob_corr" option, which modifies the interface mobility in order to mimic diffusion limited growth, is insensitive to boundary diffusion (because boundary diffusion is perpendicular to the interface normal, and thus can influence kinetics only indirectly in special cases like eutectic or eutectoid systems). Thus, using "mob_corr" for Mn will correct always for the low bulk diffusivity of Mn in both cases.
Furthermore, if the Mn diffusion field in normal direction is not sufficiently resolved, then the mobility correction will create a type of kinetic undercooling which can be much higher than the solutal undercooling of Mn. Under these conditions, changing the Mn composition e.g. by grain boundary diffusion will not have any effect anymore. I guess that this is the case in your setup.

Apart from that, your input of modification of activation energy seems reasonable. However please note that your modifications are quite huge, so that diffusion coefficients will be changed by large factors.

Bernd

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