Parameter optimization of CET simulation in arc weld

[Kim Hee Eun]

Dear Bernd,

Hello, this is Hee-Eun Kim.

I am currently attempting to simulate the columnar-to-equiaxed transition (CET) behavior in the arc weld of the CMSX-4 alloy. Based on discussions on the MICRESS forum indicating that the nucleation density model better reflects the physical mechanism, I used the default seed_density model without the lognormal option. The nucleation classes were defined to generate a total of ten classes.

Since the actual weld depth is 0.686 mm, I set the geometry z-axis to 1000 µm. Accordingly, the temperature profile along the z-axis as a function of time in the process conditions was also defined over a total depth of 0.1 cm.

When I first ran the simulation, liquid phase appeared even though the temperature was around 300 K. To resolve this, I modified the initial microstructure so that the entire z-domain started as a disordered FCC phase. However, after this modification, liquid no longer formed even when the temperature increased to 1900 K. I would appreciate your advice on this issue.

In addition, since the mushy zone of CMSX-4 is approximately between 1400 K and 1700 K, I set the nucleation temperature range within this interval. Would this be appropriate? I would also appreciate your advice on the nucleation parameters.

I have attached the dri file and the thermal history file for your reference.
Thank you always for your help.

Best regards,
Hee-Eun Kim

[Kim Hee Eun]

Dear Bernd,

I am reattaching the modified .dri file in which the liquid nucleation and initial microstructure settings have been revised.

However, liquid phase formation still does not occur in the simulation.
I would greatly appreciate your advice on this issue.

Thank you very much for your time and support.

Kim

[Bernd]

Dear Kim,

The two versions of input files which you sent have different problems why nucleation of liquid doesn't happen. In the first, there is simply no nucleation type for liquid present. In the second, you have added two further nucleation types for liquid, but they are from an L-PBF simulation and have a completely wrong time and length scale with respect to the checking interval and shield data. Therefore, it would take extremely long to get to the point where nucleation can happen.

Apart, there are at least two further things you should correct:

1.) You have a wrong initial composition because you specify the liquid composition and an "equibrium" initial condition. You should rather assign the alloy composition to the fcc-phase (phase 1) by writing:

# How shall initial concentrations be set?
# Options: input equilibrium from_file [phase number]
equilibrium 1
# ...

2.) You should not use a 1d-extension of the composition field if you plan to nucleate liquid around the top of the domain:

# 1D far field for solute diffusion
# ---------------------------------
# Enable one dimensional far field approximation for solute diffusion?
# Options: 1d_far_field 1d_far_field_EW no_1d_far_field
no_1d_far_field
# Number of cells for the 1D external field?
...

Bernd