Driving force calculation for NPLE with TQ
Posted: Tue Jun 09, 2020 3:50 am
Hi all,
I have a few questions regarding the determination of ΔG for the α-to-γ transformation with the NPLE model. Here are the questions. Say I have Fe, C and Mn:
(1) I assume that ΔG is calculated by χ(C_γ-C*_γ) in MICRESS with TQ where C_γ is the local composition, C*_γ is the "equilibrium C content in γ", and x is a factor calculated through TQ coupling (fitting ΔG vs C_γ). Is this still true for NPLE with TQ?
(2) I am trying to illustrate ΔG on a free energy vs C concentration diagram (or a ternary diagram if possible), and I started to confuse myself.
Because of the extra constraints on μ_C, μ_Mn and μ_Fe, I don't think the "parallel tangent method"* can still be used. In the case of paraequilibrium, it is possible to find the points of C contents which give μ_C,α=μ_C,γ and draw two tangent lines. Their y-intercepts when C=0 gives ΔG (see attached**). I wonder if this is still valid for NPLE even with μ_Mn,α=μ_Mn,γ and μ_Fe,α=μ_Fe,γ.
* For example, as in "Multi-ternary extrapolation scheme for efficient coupling of thermodynamic data to a multi-phase-field model" Fig. 1.
** Free energy curves were taken from B. Zhu's thesis, where "SC" denotes all substitutional elements with no C.
Thanks,
Billy
Btw, I am wrapping up my research work and thesis. I'd like to thank everyone here who has helped me on MICRESS and phase-field models, especially Bernd and Ralph!
I have a few questions regarding the determination of ΔG for the α-to-γ transformation with the NPLE model. Here are the questions. Say I have Fe, C and Mn:
(1) I assume that ΔG is calculated by χ(C_γ-C*_γ) in MICRESS with TQ where C_γ is the local composition, C*_γ is the "equilibrium C content in γ", and x is a factor calculated through TQ coupling (fitting ΔG vs C_γ). Is this still true for NPLE with TQ?
(2) I am trying to illustrate ΔG on a free energy vs C concentration diagram (or a ternary diagram if possible), and I started to confuse myself.
Because of the extra constraints on μ_C, μ_Mn and μ_Fe, I don't think the "parallel tangent method"* can still be used. In the case of paraequilibrium, it is possible to find the points of C contents which give μ_C,α=μ_C,γ and draw two tangent lines. Their y-intercepts when C=0 gives ΔG (see attached**). I wonder if this is still valid for NPLE even with μ_Mn,α=μ_Mn,γ and μ_Fe,α=μ_Fe,γ.
* For example, as in "Multi-ternary extrapolation scheme for efficient coupling of thermodynamic data to a multi-phase-field model" Fig. 1.
** Free energy curves were taken from B. Zhu's thesis, where "SC" denotes all substitutional elements with no C.
Thanks,
Billy
Btw, I am wrapping up my research work and thesis. I'd like to thank everyone here who has helped me on MICRESS and phase-field models, especially Bernd and Ralph!