Author Topic: twinning  (Read 198 times)

1034572317

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twinning
« on: March 08, 2019, 05:58:05 AM »
Dear everyone,
I want to identify the twinning in the metal Cu,however when I use DXA to identify the defect, only different  atoms were shown,and I can see different dislocations ,i want to know how to use OVITO to find  twinning deformation? Is there any other  tools such as CAT OR grain segmentation algorithm (GSA) to find it? the defect mesh in DXA include twinning?Sincerely hope your reply.

Best wishes!

wang

Alexander Stukowski

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Re: twinning
« Reply #1 on: March 08, 2019, 08:42:39 AM »
Hi Wang,

DXA only identifies the dislocation lines themselves, but it cannot tell you where twinning took place in the crystal (which isn't strictly associated with the presence of dislocations). I would say the most natural way to identify twinning is to do a strain field analysis. In OVITO you can use the Atomic Strain modifier for this. In regions of the crystal that have undergone twinning, you should see a characteristic shear strain level. As an additional criterion, you could use the Common Neighbor Analysis to restrict the selection set to perfect FCC atoms (in order to exclude HCP-like stacking fault atoms, which may exhibit the same atomic shear strain values).

-Alex

leocheng

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Re: twinning
« Reply #2 on: April 06, 2019, 09:22:54 AM »
Hello Alexander,

I want to identify the twinning and transformation in this FCC-HCP crystal after tensile deformation (as attached pictures). But I am not sure how to correctly combine CNA (Ex: Only select FCC particles and delete others ?)and Atomic Strain modifiers (Ex: how to set the Cutoff radius parameters and select the options). Moreover, by using this method, can I get the actual position(x,y,z) of where these defects took place?

many thanks,
Leo

Constanze Kalcher

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Re: twinning
« Reply #3 on: April 08, 2019, 01:38:08 PM »
Hello Leo,

just to clarify, the CNA and Atomic Strain analyses are two independent analysis methods. With the help of the CNA you already revealed that there is HCP ordering in your FCC structure, which are indicators for either a stacking fault (the red double layers) or potential twinning planes. But in order to be sure that twinning occurred, you should also compare these results to the strain field you obtain from the Atomic Strain modifier. As cutoff it is recommended that you use a value between the first and second neighbor shell. To exclude the stacking faults from the strain field color coding, you can create a selection based on the structure type and then apply the Color coding modifier only on FCC like atoms.

-Constanze