ENTER_PHASE_IN_REGION - Lamellar Prompts

The following are the ENTER_PHASE_IN_REGION subprompts for Lamellar.

For a LAMELLAR type of phase, the pearlite calculation model is invoked. The following is displayed:

eutectoid reaction is "gamma" ==> "alpha" + "beta"

This is to clarify what is meant with GAMMA, ALPHA and BETA in the specific sub-prompts that display as follows.

Subprompts

LAMELLAR
 

Enter name of "alpha" phase

Enter the GES phase name for the ALPHA phase of the eutectic/eutectoid decomposition product.
 

Enter name of "beta" phase

Enter the GES phase name for the BETA phase of the eutectic/eutectoid decomposition product.
 

Enter name of "gamma" phase

Enter the GES phase name for the GAMMA matrix phase.
 

Enter "alpha"/"beta" surface tension:

Enter function for the surface tension between the ALPHA and BETA phases, sigma function for the surface tension between the ALPHA and BETA phases
 

Enter "alpha"/"gamma" surface tension:

Enter function for the surface tension between the ALPHA and GAMMA phases,sigma function for the surface tension between the ALPHA and GAMMA phases
 

Enter "beta"/"gamma" surface tension:

Enter function for the surface tension between the BETA and GAMMA phases,sigma function for the surface tension between the BETA and GAMMA phases
 

Optimum growth condition factor /2/:

Enter the Optimum-growth-rate-factor. Due to Zener's maximum growth rate criteria this factor has a value of 2 for volume controlled growth and 3/2 for boundary controlled growth. Due to Kirkaldy's extreme in entropy production criteria the values are 3 and 2, respectively.
 

Name of dependent element

Enter the name of the substitutional element to consider as the dependent one.
 

Growth model (Volume/Boundary/Kirkaldy) for element x

Select growth model to be used for element X. Choose between:

  • Volume diffusion model
  • Boundary diffusion model
  • Kirkaldy's mixed mode diffusion model. Implies MIXED, see below.

 

df(x) = /Value/Automatic/Mixed/TDB/

Either input a numerical value on the pre-exponential factor DF or select one of the keywords:

  • AUTOMATIC
  • MIXED
  • TDB

AUTOMATIC is only available for element Carbon. It implies a mixed type of calculation where the volume diffusion part is calculated due to J. Ågren “A revised expression for the diffusivity of carbon in binary Fe-C austenite”. Scr. Metall. 20, 1507–1510 (1986) (volume diffusion of C in Austenite) and the boundary diffusion part due to J. Ågren “Computer simulations of the austenite/ferrite diffusional transformations in low alloyed steels” Acta Metall. 30, 841–851 (1982) (boundary diffusion of C is assumed to be the same as C diffusion in Ferrite).

The k' or k'', as appropriate, are given by B. Jönsson (1992)1. MIXED means a mixed mode calculation using an effective diffusion coefficient. Coefficient k' or k'' is asked for, see below. TDB means calculate the diffusion coefficient for volume diffusion for element X from the parameters stored in the database.

DQ(X)=

Input a numerical value on the activation energy DQ for element X.

k'=

k''=

Input a numerical value on the k coefficient used to calculate the effective diffusion coefficient, use in MIXED mixed mode calculations, see B. Jönsson, 1992Closed“On the Lamellar Growth of Eutectics and Eutectoids in Multicomponent Systems.” Trita-Mac 478 (January): 27.
 

DF_boundary(x)=

Input a numerical value on DF for boundary diffusion of element X in a mixed mode calculation.
 

DQ_boundary(x)=

Input a numerical value on DQ for boundary diffusion of element X in a mixed mode calculation.
 

DF_volume(x)=

Input a numerical value on DF for volume diffusion of element X in a mixed mode calculation. N.B. key word TDB may also be used, see TDB above.
 

DQ_volume(x)=

Input a numerical value on DQ for volume diffusion of element X in a mixed mode calculation.
 

Automatic start values for the s0 determination /Y/:

Enter Y if you want automatic start values for the unknown parameters in the S0 determination else enter N. S0 is the critical lamellar spacing for which the growth rate is zero.
 

Critical thickness of "alpha" lamella:

If you answered N this prompt displays. The critical thickness of ALPHA is about 0.9 of S0, which in turn is about 1/3 to 1/2 of the observed lamellar spacing S.  For binary Fe-C alloys the observed pearlite lamellar spacing is approximately given by

For binary Fe-C alloys the observed pearlite lamellar spacing is approximately given by this

The equation may be used as a start value approx. for alloyed steels. However, use the A1e temperature of the steel.
 

Critical thickness of "beta" lamella:

The critical thickness of BETA is about 0.1 of S0, see above.
 

Automatic start values on potentials /Y/:

By default, automatic start values for the unknown potentials are used. Choose N to enter your own start values.

 

Give potentials for "alpha"/"gamma" equil.

Enter start values for the unknown potentials, MU, at the ALPHA/GAMMA phase boundary.
 

Give potentials for "beta"/"gamma" equil.

Enter start values for the unknown potentials, MU, at the BETA/GAMMA phase boundary.
 

Growth rate v:

Enter a start guess on the growth rate. As a hint on what value to choose we recognize that for binary Fe-C alloys the pearlite growth rate is approximately given by:

for binary Fe-C alloys the pearlite growth rate is approximately given by this

The equation may be used as a start value approx. for alloyed steels. However, use the A1e of the steel.
 

Automatic start values on other variables /Y/:

By default there are automatic start values for the unknowns in the determination of the growth rate.
 

Fraction of "alpha" phase:

Enter a guess on the fraction of the ALPHA phase. For pearlite it is about 0.9.
 

Give potentials for "alpha"/"gamma" equil.

Enter start values for the unknown potentials, MU, at the ALPHA/GAMMA phase boundary.
 

Give potentials for "beta"/"gamma" equil.

Enter start values for the unknown potentials, MU, at the BETA/GAMMA phase boundary.