MICRESS Forum

Dear Omid,

I don't understand your phase diagram definition. First of all, you should not define component 1 as stoichiometric in 2 phases which you want to interact - that is physically not possible. Secondly, if you define the slopes for solvus and solidus with opposite sign, you define a demixing phase diagram, and you get an according warning. Thirdly, the "-999." values for slopes had been used as dummy for the stoichiometric elements (here the value and the sign do really not matter). However, you should use these values in the place of the stoichiometric elements and not in other places.

For the interface 3:3 the value of the interface energy is missing. MICRESS misinterprets some input for dG options instead which are not required. You got a corresponding warning there...

For the interface 3:3 the value of the interface is much to high - must be a typo

Phase 0 has no interaction to any other phase and hence is treated as an "inert" phase. You cannot define diffusion in inert phases...

If there is experimental evidence of grain boundary diffusion, you might include it in MICRESS using the +b diffusion option (see here).

Dear Bernd,

yes you are right about the stoichiometric definition but I since you said before that in the case of lack of database the stoichiometric definition does not have effect that much I did not care it, but sure I will revise it now.
Regarding the phase diagram I do have some infinite slopes, like when Mo3Si at the junction of Si content it is always at 25 at.% Si. the slope is infinite. I just tried to input -/+999 for the infinite definition and regarding the demixing, it is my real values! by applying this data at first some agitating happens but at the end the phase fractions and microstructures and other values completely fit the experimental observations!
I did not get exactly what you mean by: For the interface 3:3 the value of the interface is much to high - must be a typo
-I will switch off the diffusion in liquid

Regards,
Omid.

Sorry, I meant:

For the interface 3:3 the value of the interface mobility is much to high - must be a typo

Bernd

Dear Bernd,

I am still confused about how to define the super saturated phase. For the initial composition, there is a chance to define but in a liquid phase. In my case when I do have a super saturated solid phase and I need to define the initial composition in the solid domain, how can I do that?

Regards,
Omid.

Dear Omid,

you just set the initial composition of the supersaturated phase like:

# 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 ? [at%]
10.80000000
# Initial concentration of component 2 in phase 1 ? [at%]
14.50000000
...

Bernd

Dear Bernd,

I am trying to define the further nucleation part based on seed density, because I do have further nucleation in the heat treatment process and the temperature is significantly lower than the melting point. The problem is that the further nulei take place at interface but I can not find a way to define it. It seems that nucleation based on concentration is possible only on Bulk. Is there any way to solve this problem?

Regards,
Omid.

Dear Omid,

the seed density model is a special model for heterogeneous nucleation which per definition is only available for bulk nucleation. If you want to implement nucleation at grain or phase boundaries you should use the "seed_undercooling" mode which requires a critical undercooling to be defined and for which the nucleation sites can be set to "interface":

# Type of 'position' of the seeds?
# Options: bulk region interface triple quadruple [restrictive]
interface

If you need something like a density distribution of nucleation sites at interfaces, you could define various such seed types for interface nucleation with different critical undercooling and different nucleation distance or nucleation interval. This way you are able to implement any nucleation behaviour you wish!

Bernd

Dear Bernd,

Thanks for the constructive guide, It seems that defining the seed_undercooling for the interface nucleation approach has a trick! with the way of definition which I use as below, nowhere is asked for the seed type!
# Input for seed type 2:
# ----------------------
# Type of 'position' of the seeds?
# Options: bulk region interface triple quadruple [restrictive]
interface
# Phase of new grains (integer) [unresolved|add_to_grain]?
1
# Reference phase (integer) [min. and max. fraction (real)]?
3 0.9 1
# Substrate phase [2nd phase in interface]?
# (set to 3 to disable the effect of substrate curvature)
3
# maximum number of new nuclei 2?
100000
# Grain radius [micrometers]?
0.00000
# Choice of growth mode:
# Options: stabilisation analytical_curvature
stabilisation
# min. undercooling [K] (>0)?
0.0000
# Determination of nuclei orientations?
# Options: random randomZ fix range parent_relation
random
# Shield effect:
# Shield time [s] [shield phase or group number] ?
0.5
# Shield distance [micrometers] [ nucleation distance [micrometers] ]?
2.0
# Nucleation range
# min. nucleation temperature for seed type 2 [K]
0.000000
# max. nucleation temperature for seed type 2 [K]
2298.000
# Time between checks for nucleation? [s]
# Options: constant from_file
constant
# Time interval [s]
1.00000E-02
# Shall random noise be applied?
# Options: nucleation_noise no_nucleation_noise
no_nucleation_noise
Shall I add any keyword somewhere? Moreover, for the phase which solidify at 2298 K and I suppose it to be nucleated around 1400-1700 K in heat treatment process, what advices do you have to define it in the best way?

Regards,
Omid

Dear Omid,

The "trick" is that for nucleation at interfaces, the "seed_undercooling" model is default, which is the reason that you are not asked!

I do not know which your requirements for nucleation are, and whether you need different nucleation probabilities/frequencies at different critical undercoolings, or whether one fixed value (with perhaps addition of some random noise) is sufficient. Keep in mind that the more complex your nucleation model is, the more you need to know about the system, or calibrate.
Anyway, a critical undercooling of 0 K seems unrealistic because there is always a certain undercooling needed to overcome curvature of the critical seed.

Bernd

Dear Bernd,

I am trying to deal with the dri file so that I could see any movement of Si atoms but still no movement or agitation of the Si happens! Would you please check the file attached to see is there any obvious problem which prevents the movement of the Si? at the initial situation I do have a super saturated Mo solid solution with 10 at% Si, which is preliminary defined as stoichiometric composition with maximum 4 at% Si capacity. It is expected that by this sort of experimental situation like 200 MPa and amore than 1600 Ktemperature, the Si moves to boundary and with the discharged Mo atoms performs the Mo3Si phase! but still I do not see any movement of Si!!

Regards,
Omid.