Seed-density and seed-undercooling models

dendritic solidification, eutectics, peritectics,....
mauvec
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Re: Seed-density and seed-undercooling models

Post by mauvec » Fri Apr 09, 2021 6:34 pm

Hi Bernd,

Is there any example file relevant to thermal-cycle simulations that I could use for guidance in MICRESS? Otherwise, may I ask you on what steps shall I follow to perform this?

Best regards,

Mauro

Bernd
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Re: Seed-density and seed-undercooling models

Post by Bernd » Fri Apr 09, 2021 7:01 pm

Dear Mauro,

Which kind of cycling do you mean? Something like a virtual DSC experiement, or something like SLM or welding which includes melting and resolidification?

Bernd

mauvec
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Re: Seed-density and seed-undercooling models

Post by mauvec » Sat Apr 10, 2021 8:44 pm

Hi Bernd,

I meant SLM and/or welding but actually DSC type of simulation would be actually interesting to perform likewise.

Many thanks,

Mauro

Bernd
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Re: Seed-density and seed-undercooling models

Post by Bernd » Sun Apr 11, 2021 8:21 pm

Dear Mauro,

No, there is not yet a standard MICRESS example existing for these types of temperature cycling. Basically, thermal cycling is achieved in MICRESS by using time-dependent temperature boundary conditions. Depending on the type of process, they can be applied in different ways.

In case of the simulation of a DSC experiment, one would directly define a linear temperature cycle for the bottom temperature as a function of time by use of a piece-wise linear definition using "connection points".

For welding and additive processes like SLM more complex boundary conditions should be used. One option is the use of time-dependent temperature profiles which can be read from an ASCII file (again using "connection points") and which should be provided by macro- or meso-simulation tools. Another option would be using the 1d-temperature field built in in MICRESS as a thermal boundary condition. Then, the laser energy is applied as a heat flux over time at the upper boundary of the 1d-temperature field, and the temperature cycle is calculated implicitly.
However, still no standard way of doing temperature cycling has been established for this type of process.

Bernd

mauvec
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Re: Seed-density and seed-undercooling models

Post by mauvec » Wed Apr 21, 2021 11:24 pm

Dear Ralph,

I have been looking at several existing examples to explore more on how to implement the '1d_temp' field (A002_AlCu_Temp1d) and 'connecting points' (T014_Gamma_Alpha_Stress and T021_Grain_Growth_Profiles) tools. Furthermore, I also read through the great work published by Kumara et al. (2019) on the implementation of MICRESS to predict the microstructure evolution of a single deposited layer of IN718 material during direct laser energy deposition, and subsequent heat treatment. From all these, several questions arise.

From the list of examples, the 'connecting points' option is implemented so far in two different 'types of coupling' such as a) 'phase' and b) 'concentration stress', which from the context of my setup I am not sure if as an instance the 'concentration' and 'phase' types of coupling can be implemented together. The former because I would expect further formation of secondary-phases at the inter-dendritic regions after a thermal-cycle and/or during heat-treatment (DSC experiment), and the latter for coarsening effects.

Hence,

1) May I ask you if this assumption of coupling 'concentration' and 'phase' is possible?

2) If so, how would the input file should be rearranged when departing from an already predicted microstructure, considering that this encompasses liquid and solid phases? The latter because within the cross-isothermal domain that I am implementing, I am also not assisting further nucleation as in the example A006_CMSX4 (nucleation of seeds type 2 and 3) since I intentionally want to keep an inter-dendritic region of liquid/gamma.

3) From all the set of outputs generated after every simulation, there is a '.rest' file which I assume is a 'restart output' and that should be indicated somewhere in the input file (I have no idea on how to restart from a former simulation). Therefore, may I ask you on how to utilise predicted microstructures as initial input for a subsequent simulation?

4) Finally, may I ask you if the latent heat data was obtained from Thermo-calc for the example A002_AlCu_Temp1d?

Thank you for your support and taking the time to read all of these.

Best regards,

Mauro

Bernd
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Re: Seed-density and seed-undercooling models

Post by Bernd » Thu Apr 22, 2021 6:53 pm

Dear Mauro,

As Ralph is on holidays, and your questions are not too specific for him. So I will try to give you answers along your questions:

1.) Essentially, "phase" coupling means no coupling, because this means that the phase-field solver is used without coupling to any other field. So, "concentration" coupling already implicitly contains "phase" coupling.

2.) Starting a MICRESS simulation form an already simulated microstructure is possible in different ways. In earlier versions, we used the same method for reading in graphical MICRESS results (.phas or .korn output) and for reading experimental microstructures. There has been e.g. discussions of the format requirements and specific problems in the forum.
However, the preferred method nowadays is reading initial microstructures from restart-files (see below).

3.) The original idea of the restart file (.rest) was to be able to continue a simulation in case of a computer crash. To be able to continue identically as far as possible, the whole fields and numerical information required needs to be stored in the .rest file, which makes it very big. For that reason, and in view of the original purpose, we store it only for the latest output time step.
But soon the idea grew that restart can also be used for other purposes, e.g. debugging errors which appear after long simulation time, or making parameter variations for the further development of an already grown microstructure.
However, when directly restarting a simulation, only few parameters can be changed without getting compatibility issues, because the .rest-file is just a binary dump of all required data fields. The first step to get more freedom was to have the "restart reset_time" option, which disregards time and all the specific timer and temperature history informations and thus increases the number of parameters which can be modified.
Finally, the restart functionalities were further widened with "restart structure_only", which has the idea that we actually do not restart but read in an initial microstructure. In order to prevent confusion, from version 7 on we restructured the input such that this new functionality is separated from the restart functionality. Now, continuing a simulation is offered at the top of the input file ("Restart"), while reading an initial microstructure from one or more restart files is possible in section "Initial Microstructure".

4.) No, it was not, although this is well possible. Instead, data was iteratively obtained from the .dTLat output, which is written always if latent heat is requested. As a starter, a simulation without couling to latent heat but with latent heat output ("no_lat_heat_dsc") can be performed for getting a .dTLat file with approximated start values.

Bernd

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