Guten Morgen
Mr. Bernd,
Could you please let us know, how to decide which phases to include in thermocalc and which ones to reject. For eg Alloy AlCu.
Danke im Vorraus
---
original message from Raghav
Selection of Phases for thermocalc (Micress)
Re: Selection of Phases for thermocalc (Micress)
Guten Tag Raghav!
First welcome in the micress forum!
You are raising an interesting question. I will try to give a rather general answer, because there is no single and clear way how to find out the relevant phases for a micress simulation. There are several approaches and considerations about this topic:
1.) If you use all phases in micress which are listed in the database you can be sure not to miss anyone of them! This is trivial but I would not advise to do so. The consequence would be a very large driving file, very poor performance and, probably also numerical problems when nucleation is checked for some special phases which are far from beeing stable, or which definitively contain elements which are not considered in the simulation. If you try this approach you should at least remove the phases which definitively cannot form!
2.) In many cases you will not be interested to put all phases into the simulation which could be formed at some place. If you e.g. are going for an investigation of the DAS (secondary dendrite arm spacing) of the primary phase, there is no need to include all phases which could form in the interdendritic region. One would just stop the simulation at the temperature at which precipitation of the interdendritic phases starts, and evaluate the DAS at this time.
3.) If a solidification simulation is inteded to be performed with micress, the Thermo-Calc Scheil model may be a good approximation for finding out which phases are forming in which temperature range. Strong back diffusion or strong kinetic effects would make this approximation less appropriate.
To increase the probability for finding all relevant phases, additional Scheil simulations with slightly modified composition can be performed.
4.) For simulations including solid-solid reactions (like homogenisation, precipitation of solid phases during life-time, etc.) the equilibrium approximation may be better. A calculation of the phases present in equilibrium in the relevant temperature interval using Thermo-Calc (or, of course some similar software like Pandat, Chemsage, etc. ) would give the set of relevant phases for MICRESS. If solidification is also included in the micress simulation, the phases from the Scheil simulation should also been taken into account.
5.) If there are experiments available at least the phases found in these experiments should be included.
For the case of AlCu and solidification, a Scheil simulation should be sufficient to find out the relevant phases during solidfication, and an Thermo-Calc equilibrium calculation for solid-solid stuff. Probably you can also find them directly in the binary phase diagram!
I hope this answers your question!
Bernd
---
original message from Bernd
First welcome in the micress forum!
You are raising an interesting question. I will try to give a rather general answer, because there is no single and clear way how to find out the relevant phases for a micress simulation. There are several approaches and considerations about this topic:
1.) If you use all phases in micress which are listed in the database you can be sure not to miss anyone of them! This is trivial but I would not advise to do so. The consequence would be a very large driving file, very poor performance and, probably also numerical problems when nucleation is checked for some special phases which are far from beeing stable, or which definitively contain elements which are not considered in the simulation. If you try this approach you should at least remove the phases which definitively cannot form!
2.) In many cases you will not be interested to put all phases into the simulation which could be formed at some place. If you e.g. are going for an investigation of the DAS (secondary dendrite arm spacing) of the primary phase, there is no need to include all phases which could form in the interdendritic region. One would just stop the simulation at the temperature at which precipitation of the interdendritic phases starts, and evaluate the DAS at this time.
3.) If a solidification simulation is inteded to be performed with micress, the Thermo-Calc Scheil model may be a good approximation for finding out which phases are forming in which temperature range. Strong back diffusion or strong kinetic effects would make this approximation less appropriate.
To increase the probability for finding all relevant phases, additional Scheil simulations with slightly modified composition can be performed.
4.) For simulations including solid-solid reactions (like homogenisation, precipitation of solid phases during life-time, etc.) the equilibrium approximation may be better. A calculation of the phases present in equilibrium in the relevant temperature interval using Thermo-Calc (or, of course some similar software like Pandat, Chemsage, etc. ) would give the set of relevant phases for MICRESS. If solidification is also included in the micress simulation, the phases from the Scheil simulation should also been taken into account.
5.) If there are experiments available at least the phases found in these experiments should be included.
For the case of AlCu and solidification, a Scheil simulation should be sufficient to find out the relevant phases during solidfication, and an Thermo-Calc equilibrium calculation for solid-solid stuff. Probably you can also find them directly in the binary phase diagram!
I hope this answers your question!
Bernd
---
original message from Bernd