Follow-up Inquiry on MICRESS Capabilities for Dislocation-Precipitate Studies

[yimi_rui]

Hi,bernd.Sorry to bother you again. I debugged the phase diagram parameters in the driving file and finally simulated the growth process of Cr precipitates. The key parameters I modified are:
T0 [K] ?
1100
c0 of component 1 in phase 1 ? [wt%]
0.1228
c0 of component 1 in phase 2 ? [wt%]
4.8768000E-03
In previous simulations, for the value of "c0 of component 1 in phase 2 ? [wt%]", based on the phase diagrams (see Fig1, Fig2), I assumed that the content of Cr element (component 1) in the Cr precipitate phase (phase 2) should approach 99%, but the simulation failed at this time. When I adjusted the content of Cr element (component 1) in the Cr precipitate phase (phase 2) to a very small value, the precipitation phase simulation proceeded normally. Why is this?

It can also refer to the output after "Beginning of initialisation" in the scr file:
Equilibrium temperature T_Glgew = 1141.2000 K
Phase 1, Component 0: 99.83600
Phase 1, Component 1:0.1640000
Phase 2, Component 0: 99.99924
Phase 2, Component 1:7.5680000E-04
The precipitate phase can only form or grow when "Phase 2, Component 1" is very small (approaching 0). Does this contradict the phase diagram rules?

Thanks for your time and help!

[yimi_rui]

Hi,bernd.I guess the elements for component 1 and component 0 are set mixed up. That is, component 1 is the Cr element. But in this case, the c0 of component 1 in phase 2? [wt%] being 4.8768000E-03 makes sense, while the c0 of component 1 in phase 1? [wt%] being 0.1228 doesn't make sense!

[Bernd]

Dear yimi_rui,

You define yourself which component is which by defining the corresponding slopes and c0 values. Given that you have a material which is rich in Cu it makes sense to define Cu as matrix element (component 0) and Cr as component 1. Then you draw the isotherm line for a temperature where both phases are existing (e.g. 1149 K) and obtain the values of c0 and m at this temperature. I don't understand from where you took your values.

According to your phase diagram, for the case of 1194 K, the values of the Cr composition (component 1) are approximately 0.027 in phase 1 (point A) and 0.9998 in phase 2 (point B). 0.0164 is the eutectic composition which is not of interest for you, because you do not simulate solidification!

Bernd

[yimi_rui]

Dear Bernd，

When setting the phase diagram input, the Cr composition values are approximately 0.0027 (mole fraction) in phase 1 (point A), which converts to 0.22 wt% as the mass fraction, and 0.9998 (mole fraction) in phase 2 (point B), corresponding to 99.98 wt%. The input statements in the driving file were written as:
#c0 of component 1 in phase 1 ? [wt%]
0.22
#c0 of component 1 in phase 2 ? [wt%]
99.98

However, this input failed to simulate the precipitation phase growth process. It was only when the input was adjusted to:
#c0 of component 1 in phase 1 ? [wt%]
0.22
#c0 of component 1 in phase 2 ? [wt%]
0.005 （or a value with three decimal places）—that is, when the Cr content in the precipitated phase was very low, the program successfully simulated the precipitation phase growth.
May I ask why this happened?

yimi_rui

[Bernd]

Dear yimi_rui,

It does not make any sense to set c0 of Cr in phase 2 to 0.005. Thus, any results you may get this way are meaningless.

There must be a reason why your setup with the correct equilibrium compositions does not work. Can you tell me which initial Cr composition you use for the alloy? Maybe it is too small to allow the formation of reasonable amounts of phase 2.

Bernd

[yimi_rui]

Dear Bernd，

The initial Cr content I set in phase1 is 0.14 wt%, and the initial temperature(at the bottom) is 1100K. (The reason for setting the initial Cr concentration at 0.14 wt% is that the maximum solubility of Cr in phase1 is approximately 0.002 mole fraction at 1100K, which converts to approximately 0.16 wt% in mass fraction.) To ensure that the initial Cr concentration falls within the single-phase region of phase1, the initial Cr concentration should be lower than 0.16 wt%, so I used a value of 0.14 wt%. I wonder if my understanding here is correct? The code in the driving file should be input as:

# Input of the phase diagram of phase 1 and phase 2:
# --------------------------------------------------
# Which phase diagram is to be used?
# Options: linear linearTQ
linearTQ
# Please input linearisation data in the TQ format!
# T0 [K] ?
1149.8
# dG [J/cm**3] ?
0
# dSf+ [J/cm**3K] ?
1
# dSf- [J/cm**3K] ?
-1
# dH [J/cm**3] (dummy)?
10
# c0 of component 1 in phase 1 ? [wt%]
0.22
# c0 of component 1 in phase 2 ? [wt%]
99.95
# m of component 1 in phase 1 ? [K/wt%]
1000
# m of component 1 in phase 2 ? [K/wt%]
-10000
# dcdT of component 1 in phase 1 ? [wt%/K]
0
# dcdT of component 1 in phase 2 ? [wt%/K]
0

# Initial concentrations
# ======================
# How shall initial concentrations be set?
# Options: input equilibrium from_file [phase number]
equilibrium 1
# Initial concentration of component 1 in phase 1 ? [wt%]
0.1400000000

# License check
# =============

# Parameters for latent heat and 1D temperature field
# ===================================================
# Simulate release of latent heat?
# Options: lat_heat lat_heat_3d[matrix phase] no_lat_heat no_lat_heat_dsc
no_lat_heat

# Boundary conditions
# ===================
# Type of temperature trend?
# Options: linear linear_from_file profiles_from_file
linear
# Number of connecting points? (integer)
0
# Initial temperature at the bottom? (real) [K]
1100.000

When I checked the scr.txt file, I found that after the undercooling condition was achieved at 10s, phase2 nucleated, but it quickly disappeared at 10.00342 s. Then it nucleated again at 10.100 s and disappeared at 10.10256 s... Why does this happen?

yimi_rui

[Bernd]

Dear yimi_rui,

According to the scr.txt file which you attached, you apply a strong cut on the driving force in the phase interaction data of phases 1/2:

avg 0.5 max 1

As a result, the driving force is cut to a maximum of +/-1 J/cm3, regardless how big is the undercooling. This is not enough to overcome curvature and most probably the reason why the nuclei vanish after short time. Cutting the driving force does not make sense in this context, please remove the bold part of this line in your input file.

Bernd

[yimi_rui]

Hi Bernd,

I deleted "max 1" from the driving file as you suggested (just want to confirm if my understanding was correct). However, after running the driving file, the result remains basically the same: many phase 2 seeds appear at 10s, but phase 2 disappears shortly afterward. I'm really confused and can't figure out where the problem is.

Looking forward to your further guidance!


yimi_rui

[Bernd]

Hi yimi_rui,

I think a further problem could be the sign of the dSf+ and dSf- in the phase diagram description - probably they must be reversed:

# dSf+ [J/cm**3K] ?
-1
# dSf- [J/cm**3K] ?
1

If this is also not solving the problem, please send the input file so that I can try myself.

Bernd

[yimi_rui]

Hi Bernd, I've modified the driving file, but the simulation of precipitate phase still failed. I'm sending you the input file. Would you please help check it? Thank you very much for your assistance!