Simulation of solidification of Gamma prime alloy during SLM process

dendritic solidification, eutectics, peritectics,....
CharMIC
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Re: Simulation of solidification of Gamma prime alloy during SLM process

Post by CharMIC » Wed Jan 08, 2020 3:24 am

Hi Bernd

In MC phase, apart from C, Cr and Al composition reach values that is more than 10 times its usual values. Hf, Ta and Ti do not fluctuate.

However, in fcc phase almost all the element fluctuate. see the attached image. in the image I have defined isolines with values -0.01 and 50 at%.

# 0 -> NI
# 1 -> CR
# 2 -> CO
# 3 -> MO
# 4 -> W
# 5 -> TA
# 6 -> AL
# 7 -> TI
# 8 -> HF
# 9 -> C
Attachments
FCC_composition_at.pct..PNG
FCC_composition_at.pct..PNG (207.51 KiB) Viewed 1496 times

Bernd
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Re: Simulation of solidification of Gamma prime alloy during SLM process

Post by Bernd » Wed Jan 08, 2020 12:07 pm

Hi Chamara,

Like I have outlined recently, MC carbides are one of the most difficult type of precipitates, and many parameter settings affect their behaviour. Maybe the fastest way to get further is that you send me the complete input files so that I can run the simulation myself.

Bernd

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

Re: Simulation of solidification of Gamma prime alloy during SLM process

Post by Bernd » Fri Jan 10, 2020 3:46 pm

Hi Chamara,

I got your files and are running them and to try some ideas what could help. It takes some time for running, so I will tell you about the results on Monday...

Bernd

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

Re: Simulation of solidification of Gamma prime alloy during SLM process

Post by Bernd » Wed Jan 15, 2020 12:06 am

Hi Chamara,

I could not find anything specific which would be wrong in your input file, apart from the general difficulties with MC carbides which I mentioned above. In such cases, there is no other option than to try out what could help. Essentially, I tried several modifications in order to prevent or reduce the error messages. I did not question the general numerical setup (interface mobility, resolution, etc.), because it seems reasonable. What I tried was

1.) Using reasonable limits for fcc (0-20at%) in order to prevent switching of fcc to MC
2.) Using "solubility_on" before defining the stoichiometric condition of the carbide-forming elements Hf, Ta, W. This essentially allows using the composition of these elements in MC as start condition for quasi-equilibrium calculation when the phase fraction of MC is high.
3.) Using "globalG" as relinearisation option for the solid-solid interactions (1/2 and 1/3) in order to prevent numerical difficulties due to interfaces which consist of one or few grid cells
4.) Using diffusion inside MC to prevent gradients inside the precipitates
5.) Using some diffusion in γ'
6.) Remove off-diagonal terms for diffusion in fcc

Although most modifications somehow seem to reduce the number of error messages slightly, only 3.) "globalG" had a strong effect, reducing the number of error messages from over 8000 to 59. With this modification also the negative compositions are removed, and the simulation gets a bit faster, so you probably can live with them. Of course, you can try other things in combination with globalG. I think the specific difficulty here is that MC is rapidly overgrown by γ', which has no solubility at all for carbon while MC has only a small solubility limit for this element...

Bernd

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