Dear Shubhansu Singh,
The molar volume is obtained in Thermo-Calc through the "VM" variable and is given in m3/mol (see for instance p.9 of the TCNI11 Technical Information https://thermocalc.com/content/uploads/Documentation/Databases/Thermodynamic/tcni11-technical-info.pdf).
For the lattice parameters, this information is not really included in the databases, so it can only be calculated for cubic phases (it is mentioned in this brief description of the TCNI8 database https://www.engineering-eye.com/THERMOCALC/details/db/pdf/thermo-calc/02/tcni8.pdf).
There is no variable attributed to the lattice parameter, so you have to enter a custom function to compute it from "VM" by yourself. You can find examples in the FCC and BCC cases p.1535 of the following documentation set: https://www.thermocalc.com/content/uploads/Documentation/Current_Static/thermo-calc-documentation-set.pdf.
To compute the density, you can also enter a used-defined function such as density = VM**(-1).
Maybe it will be easier to simply compute the molar volume "VM" from your database, and then to do the data treatment to obtain the density or lattice parameters using your favorite data analysis software.
Please note that information on the molar volume are rarely included in the thermodynamic databases, and for the TCNI10 database this property is available for “the most important systems” and “for most phases of importance” (i.e. your calculations will not be valid for any composition).
Best regards,
Guillaume
Dear, Guillaume Deffrennes
Thankyou for your response, I would also like to know if calculation of density as a function of temperature can be correctly predicted for superalloys by Thermocalc (database TCNI10).
Best Regards,
Shubhansu Singh
Dear Shubhansu Singh,
Strictly speaking, Thermo-Calc databases that are built using the CALPHAD approach cannot really do predictions.
However, a major strength of CALPHAD lies in the extrapolation possibilities to multicomponent systems.
It means that based mostly on the data available on the binary (Ni-Fe, Ni-Co, …) and ternary (Ni-Fe-Co, …) systems, you can compute accurately properties for complex alloy systems (such as Ni-Fe-Co-Cr-…).
So, in your case of interest, the reliability of your calculations depends on what density data are available in the temperature - composition space.
Usually, density measurements on alloys are scarce, especially on solid phases. I don’t have knowledge of the literature on the density of Ni superalloys, but from a quick search it seems to be no exception. This is probably why on the TCNI10 documentation sets, it is written:
“However, it should be noted that the molar volume data only provides rough estimations […].”
https://thermocalc.com/content/uploads/Documentation/Databases/Thermodynamic/tcni10-technical-info.pdf
So, it really depends on which particular alloys you are working with, and what accuracy you need. Once you established that, I would suggest you to contact Thermo-Calc technical support to ask them if TCNI10 can work for your specific purpose.
Kind regards,
Guillaume
Dear Dr. Guillaume Deffrennes,
According to your answer to Mr. Shubhansu Singh, one question that comes to me is that for the molar volume calculation of the different steel grades ( multicomponent steels) Termo-calc database could be reliable or not?
If not, could you please suggest other methods or software for the calculation of Molar volume and density, especially for multicomponent steels, which are reliable in this matter?
Dear Tahereh Zargar ,
I don't know how reliable the TCFE database is for molar volume calculations.
In the TCFE12 database manual, it is simply written that "all necessary volume data (including molar volume and thermal expansion) has been updated for all phases" since the 2015 release.
The Thermo-Calc support team will know best if there are domains where the calculations are less reliable.
I believe it is a good practice to start by comparing the calculations with some data on the alloys you are interested in before you start using the database.
The CALPHAD method used in Thermo-Calc database is very adequate to model the molar volume of mulicomponent alloys, the problem is whether or not there is data. If you are looking for an introduction : Article CALPHAD modeling of molar volume
TCFE database may very well be reliable for your purpose, but if you are looking for another software, Pandat by Computherm could also work for you (https://computherm.com/docs/pandat-database-manual/molar-volume-database-manual/molar-volume-database-of-fe-alloys).
Best regards,
Guillaume
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