Search found 84 matches

by zhubq
Wed Dec 07, 2011 2:41 am
Forum: thermodynamics
Topic: thermodymics problem
Replies: 3
Views: 2343

thermodymics problem

Hi, Bernd. I have a fundamental question about thermodymics. Take Fe-C system as an example. How to calculate the driving pressure when the temperature is above the ferrite-to-austenite transition temperature (912C for pure iron)? The reference carbon concentration at the same temperature will be ne...
by zhubq
Mon Jul 18, 2011 9:04 pm
Forum: thermodynamics
Topic: entropy difference between two phases
Replies: 16
Views: 7033

Re: entropy difference between two phases

Ok. Now I see. you use the average molar volume.
by zhubq
Thu Jul 14, 2011 8:14 pm
Forum: thermodynamics
Topic: entropy difference between two phases
Replies: 16
Views: 7033

Re: entropy difference between two phases

Hi, Bernd. the unit of entropy in MICRESS is J/m^3/K. So if we get J/mol/k, we have to transit the unit with molar volume. when I derive the entropy difference from Thermo-Calc, I divided it by the molar volume of the "ENTERED" phase. I think that is also why we have to input the molar volume of eac...
by zhubq
Mon Jul 04, 2011 8:35 am
Forum: pre-processing
Topic: nucleation issues
Replies: 16
Views: 6177

Re: nucleation issues

Hi Ben, This is right. It must be like that, otherwise the mass balance is violated! It is also the reason why we are mostly using the "small grain" model for nucleation: If only a small fraction in one cell is used as initial seed, composition balance can be fulfilled without starting from a compl...
by zhubq
Thu Jun 30, 2011 11:39 pm
Forum: thermodynamics
Topic: entropy difference between two phases
Replies: 16
Views: 7033

entropy difference between two phases

Hi, Bernd How do we get the entropy difference between two phase e.g. austenite and ferrite from Thermo-calc? What I did is : input the steel chemistry, get the equilibrium compositions of the two phases at a specific temperature, and the volumetric entropy of each phase. Then get the difference of ...
by zhubq
Wed Jun 29, 2011 11:18 pm
Forum: pre-processing
Topic: nucleation issues
Replies: 16
Views: 6177

Re: nucleation issues

Hi, Bernd.

when nuclei are put in the domain, does the nuclei have the same solute content as the parent phase in order to keep mass balance?

Thank you.

Ben
by zhubq
Mon Jun 27, 2011 8:23 pm
Forum: phase-field model
Topic: Gibbs-Tompson effect
Replies: 4
Views: 2711

Re: Gibbs-Tompson effect

Hi, Bernd. You are quite right. I made a mistake :oops: Hi zhubq, no, I do not agree at all! Local curvature gives and additional contribution to the total driving force. If the interface is in local equilibrium (total driving force is 0), then the chemical driving force must compensate for thát, an...
by zhubq
Tue Jun 21, 2011 1:32 am
Forum: phase-field model
Topic: Gibbs-Tompson effect
Replies: 4
Views: 2711

Gibbs-Tompson effect

Hi, I am doing carbide precipitation/dissolution. I found that in MICRESS, Gibbs-Tompson effect cannot affect the thermodynamics e.g. the equilibrium concentration at the interface but affect the kinetics. So it is different from the classical theory if the interface is diffusion-controlled. Do you ...
by zhubq
Tue May 24, 2011 11:36 pm
Forum: phase-field model
Topic: mass blance
Replies: 2
Views: 1852

Re: mass blance

Hi zhubq, for exactly this reason, we are using double precision (R8) in MICRESS for the diffusion solver, even if the memory usage is higher! We found the strongest problems when using the 1d extension of the concentration field with long-range diffusion profiles. Of course, one can try to reduce ...
by zhubq
Fri May 20, 2011 9:38 pm
Forum: phase-field model
Topic: mass blance
Replies: 2
Views: 1852

mass blance

Hi, Bernd when I run a diffusional transformation simulation, I find that MICRESS could keep the mass balance accurately during the whole simulation. But in my own codes, I found that the mass balance cannot be kept exactly, there is always accumulated error (maybe quite small every iteration) and t...