Issues with FA-mode Solidification Simulation and slow-down

[Ku shihyeon]

Hi, I am currently conducting simulations on the development of solidification microstructures for stainless steel alloys,
specifically focusing on F, FA, and A solidification modes.

I am presently working on the FA (Ferritic-Austenitic) mode, but I have encountered several problems
In the attached stainless.dri file, I have included the Austenite (FCC), Ferrite (BCC), and Sigma phases.
I have also configured the nucleation seeds to account for all stages, from F-A solidification and nucleation to sigma precipitation during the post-solidification thermal history.

Specifically, the FA mode solidification is modeled through the following stages;
Stage 1: Growth of primary ferritic dendrites.
Stage 2: Nucleation and growth of austenite at the interface between the liquid and the ferritic dendrite edge
Stage 3: Consumption of the ferritic dendrites by austenite, proceeding from the Austenite / Ferrite interface toward the dendritic core (F to A solid-state transformation), resulting in a vermicular (skeletal) ferrite morphology within an austenite matrix.
Stage 4: Simulation of sigma precipitation by applying a high-temperature thermal history to the final solidified microstructure.

For now, the F-A solidification and solute redistribution are highly unstable(image attached), and simulation is extremely slow.

stainless.png

(image from stainless.dri)

To address this, I have simplified the code to first implement a basic primary ferrite single-phase solidification (stainless4.dri).
I anticipate that stabilizing the complex F-A solidification microstructure can be achieved by optimizing parameters such as interfacial energy, anisotropy, and anisotropic stiffness for the Liquid/F, Liquid/A, and F/A interfaces.
I would greatly appreciate any advice or precautions regarding the implementation of these solidification processes and microstructures.

Furthermore, I am currently struggling even with the simplified single-phase ferrite solidification.
The primary issue is the abnormal simulation time.
Despite adjusting the re-linearization interval, diffusion recalculation interval, and PF solver time step,
the calculation remains extremely slow.

After the initial step, the simulation effectively stalls.
The log outputs the following:

Intermediate output for t = 1.00000E-36 s
CPU-time: 2 s
Current phase-field solver time step = 6.48E-08 s
Average conc. of comp. CR = 20.0383059, Variation = +0.0000000 wt%
Average conc. of comp. NI = 14.8802462, Variation = -0.0000000 wt%
Average conc. of comp. MO = 2.0113571, Variation = -0.0000000 wt%
Temperature at the bottom = 1710.00000 K
Temperature gradient = 0.00000 K/cm

Approximately 10 to 20 minutes after this output, the line "Updating of diffusion data from database..." appears,
but no further progress is made for several dozen minutes.
Could you identify what might be causing this problem?
I have attached the latest simplified file (stainless4.dri) along with the TCM and GESS files used for the calculation.

Thank you for your assistance and looking forward to your advice.

Best regards, Ku