## How grain boundary diffusion works

technical aspects of .dri file generation (e.g. debug mode ) etc...
Hamid
Posts: 15
Joined: Fri Feb 27, 2009 1:47 am

### Re: How grain boundary diffusion works

Then, the value for f is 1/8 not 8 as you mentioned above Am I right?
Hamid

Bernd
Posts: 1042
Joined: Mon Jun 23, 2008 9:29 pm

### Re: How grain boundary diffusion works

No,

=
therefore f must be 8 to compensate!

Bernd

Hamid
Posts: 15
Joined: Fri Feb 27, 2009 1:47 am

### Re: How grain boundary diffusion works

Agree.

Thank you again,
Hamid

CharMIC
Posts: 183
Joined: Mon Aug 21, 2017 5:01 pm
anti_bot: 333

### Re: How grain boundary diffusion works

Bernd wrote:Dear all,

Grain boundary diffusion is available in MICRESS since more than 2 years, but nearly nobody used it up to now. It also has never been documented in detail. (but in the new manuals we are working on, it will of course be included!)

Grain boundary diffusion in MICRESS is implemented as an increased diffusivity of a phase in the interface region to other phases. This increase is expressed as a reduction of the activation energy, leading to a temperature-dependent factor on the diffusion coefficients. The user has to specify this activation energy correction in J/mol as well as the physical interface thickness which is needed to scale to some real thickness. Thus, grain boundary diffusion is only possible for elements in phases which have also diffusion in the bulk and not e.g. for stoichiometric intermetallics without solubility range!

The input works only in the terse mode, i.e. if each diffusion term is defined with a proceeding element and phase number. First, bulk diffusion has to be defined for this contribution. Afterwards, for the same contribution, grain boundary diffusion can be added by using the keyword "+b", followed by a string with length <number of phases +1> consisting of "n" or "b". This string defines for each phase whether in grain boundaries to the actual phase enhanced diffusion is to be considered. For each "b" character, an actication energy difference and a physical interface thickness has to be entered in extra lines, e.g.(ternary alloy, 3 solid phases):

# How shall diffusion of component 1 in phase 1 be solved?
1 1 multi gg
# How shall diffusion of component 2 in phase 1 be solved?
2 1 multi gg
# How shall diffusion of component 1 in phase 1 be solved?
1 1 +b nnbn
# Grain boundary diffusion settings for component
# 1 at boundary of phases 1 and 2:
Correction for activation energy? [J/mol]
1.8E3
Physical width of the interface? [nm]
2.5
...
end_diffusion_data

Bernd

Hej Bernd,

I did not understand the meaning of syntax "nnbn" could you bit explain what does this order mean.

BR
Chamara

Bernd
Posts: 1042
Joined: Mon Jun 23, 2008 9:29 pm

### Re: How grain boundary diffusion works

Dear Chamara,
# How shall diffusion of component 1 in phase 1 be solved?
1 1 +b nnbn
means the following:

For diffusion of component 1 in phase 1, the following boundary diffusion is added ("+b"):
Interfaces with phase 0: no ("n")
Interfaces with phase 1: no ("n")
Interfaces with phase 2: yes ("b")
Interfaces with phase 3: no ("n")

That means, in effect, enhanced diffusion of component 1 in phase 1 inside 1/2-Interfaces is considered. The amount of the enhancement is specified in the following 2 lines (for each "b").
As you see, an interface cannot have an extra diffusivity without reference to a phase (here: phase1)!

Bernd