Pearlite-to-austenite transformation

solid-solid phase transformations, influence of stresses and strains
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Pearlite-to-austenite transformation

Post by pmecozzi » Thu Oct 27, 2022 4:00 pm

Dear Bernd,

We are currently simulating the pearlite to austenite transformation during heating at 10 °C/s.
We set both the ferrite and the cementite as anisotropic phases and the ferrite/austenite and cementite/austenite interface mobility not null for special misorientation. Our aim is to let austenite grow in the ferrite and the cementite within a given colony.
However, we discovered some anomalies during the austenite growth. The austenite nucleated at the ferrite /colony 1 interface grows in both ferrite and cementite (see the picture), consistently with the input mobility.
On the contrary, the austenite nucleated at the boundary between the two colonies grows only into the ferrite. We do not understand why the mobility of the cementite/austenite interface is zero in this case, although we set for that misorientation a mobility not null.
I attach the driving file and the orientation, mobility and interface output showing the different behaviour of the austenite grains growing in colony 1 and in colony 2.
Please let me know if you need other results files.

Kind Regards,

Austenite_in_colony_2.png (64.56 KiB) Viewed 3949 times
Austenite_in_colony_1.png (68.99 KiB) Viewed 3949 times
Entire_domain.png (29.21 KiB) Viewed 3949 times
(39.22 KiB) Downloaded 138 times

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Re: Pearlite-to-austenite transformation

Post by janin » Fri Nov 04, 2022 10:07 pm

Dear Pina,
great to see you working on such interesting simulations! I couldn't run your simulation without the input structure, but I guess the critical point is that you defined austenite with tetragonal symmetry. This means, it can nucleate in two different variants with special orientation relation (SPO) to the parent cubic ferrite. (Micress uses a random number to consider both variants with equal probablility). The SPO that you defined for misorientation with cementite (33°,57°) only only holds for one of the two austenite variants. In one variant it will interact with cementite, but in the other not.
The most straightforward and natural solution should be to change the symmetry of austenite to cubic. In case that you need the tetragonal symmetry for some special reason, you could alternatively define SPOs for all possible austenite-cementite misorientations (i.e. 33°,57°,123°,147°).
I hope this will solve your problem, if not, please let me know.
With best regards,

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