Data for further nucleation

dendritic solidification, eutectics, peritectics,....
Bernd
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Re: Data for further nucleation

Postby Bernd » Fri Oct 12, 2018 7:23 pm

Hi Chamara,

The classical method (which you should know from the Basic MICRESS Training ;) ) is to use different seed types for bulk, interfaces and triple junctions, and then assign different critical undercooling (using the "seed_undercooling" model).

The only alternative I can imagine would be to spatially resolve the critical nucleus (e.g. seed particle). Then, while nucleating at the interface of the seed particle, a grain boundary would help the seed to overcome the critical curvature. However, I don't know how this could work in solid state, where nucleation probably occurs on defects or dislocations...

Bernd

CharMIC
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Re: Data for further nucleation

Postby CharMIC » Fri Oct 12, 2018 8:40 pm

Hi Bernd,

Actually I thought about the classical method you have mentioned. But was not sure if its the right path to take. I thought may be there might be other special models in MICRESS for this.

BR
chamara

CharMIC
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Re: Data for further nucleation

Postby CharMIC » Thu Jan 10, 2019 11:01 am

Hi Bernd,

Consider the following case.

I want to set nucleation r distance to each other. The nucleation will be checked at dt intervals. Initial nucleation will be checked at t0. When the nucleation is checked at t0, the average distance of the seeds will be around r. However when the nucleation checked at t0+dt, the new seeds will nucleate at an average distance of r to each other. However they will also nucleate close (< r) to the seeds that were precipitated at t0.

If I want the seeds that nucleate at t0+dt to nucleate at an average distance r to the previously nucleated seeds at t0, how should I do it.

BR
Chamara

Bernd
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Joined: Mon Jun 23, 2008 9:29 pm

Re: Data for further nucleation

Postby Bernd » Fri Jan 11, 2019 12:30 am

Hi Chamara,

For this purpose you would use a shield distance equal to r, and a shield time > dt. The optional parameter "nucleation distance", if set to a value < r would increase the number of checked points, but never override the shield distance, even at t0.

Bernd

CharMIC
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Re: Data for further nucleation

Postby CharMIC » Fri Jan 11, 2019 10:41 am

Hi Bernd,

Thanks for your input. I did as you told. I put shield time 5000s and nucleation checking for 20s. And I set shield distance for 50nm and nucleation distance for 10nm. However, when the nucleation happens, distance between particles become around 10nm. see the image. It seems like it override the shield distance?
Attachments
nucleation distance.PNG
nucleation distance.PNG (60.76 KiB) Viewed 4 times

Bernd
Posts: 978
Joined: Mon Jun 23, 2008 9:29 pm

Re: Data for further nucleation

Postby Bernd » Fri Jan 11, 2019 1:23 pm

Hi Chamara,

Yes, you are right! I looked it up in the code, and nucleation in the same time step only recognizes the nucleation distance and not the shield distance. This is reasonable in the sense that the shield is some physical (thermal or solutal) effect which would not exist if nuclei really would form simultaneously.
Thus, as in reality exactly simultaneous nucleation is rare anyway, one should in most cases use the nucleation distance equal (=default) or bigger than the shield distance. A reasonable strategy is to increase the nucleation distance but at the same time decrease the checking interval dt such that a sufficiently high "checking density" is reached without increasing the calculation time too much.

Bernd


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