Twin identification and discrepancies with CHANNEL5

[Matteo Demurtas]

Hi everyone,

I'm having problems on some newly collected EBSD maps, more specifically regarding the identification of twins in calcite. I have a MTEX script that is working perfectly on older maps, but seems not to do its job on the new ones (see attached script).
In particular, I've also noticed that in some cases the grain boundary angles within twinned calcite grains correspond to the angle that appears if I do a misorientation profile in CHANNEL5, but in other cases is different, which makes no sense to me (see attached figured as an example).

Does anyone has an idea on why that change in the grain boundary angle, and why the script is not recognizing the twin boundary even if it is at 78 degrees as it should be?

Cheers,

Matteo

%Define the misorientation axis
twindir_cal = Miller(2,0,-2,1,ebsd('Calcite').CS,'UVTW')
%Define the twinning misorientation
twin_cal = orientation('axis',twindir_cal,'angle',78*degree,ebsd('Calcite').CS,ebsd('Calcite').CS)
%Check the angle between boundary misorientations and twinning
%misorientation is small
gbcal = grains.boundary('Calcite','Calcite');
istwinning_cal = angle(gbcal.misorientation,twin_cal) < 5*degree;
%Isolate twins boundary
twinboundary_cal = gbcal(istwinning_cal);

[ruediger Kilian]

Hi Matteo,
have you checked that your crystal symmetry is correct? Could you post two of the affected orientations (one of each domain should be fine) and the CS.
Cheers,
Rüdiger

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[Matteo Demurtas]

Hi Ruediger,

they crystal symmetry that I use is always the same both for the old and new maps, which for calcite is

% crystal symmetry
CS = {...
  'notIndexed',...
  crystalSymmetry('-3m1', [4.99 4.99 17.064], 'X||a', 'Y||b*', 'Z||c', 'mineral', 'Calcite', 'color', 'light blue');

In the image attached I inserted the orientation in Euler angles of both the host and the twin for the two grains.

Cheers
Matteo

[Thomas Simm]

Hi,

Just a thought but have you double checked your settings when importing to MTEX are correct? See below and the pdf in this thread from Jessica https://groups.google.com/forum/#!topic/mtexmail/9mGJ92pD-8U

Thomas

Validate your settings
Note that the above are settings I have used for our system and verified to be accurate.
I strongly suggest you compare the mtex results to those from the EBSD acquisition
system (which should hopefully be right). To do this, save an image of a map (say IPF in
x) from Brucker, and compare it to one plotted with Mtex which can be seen by
clicking the 'plot' button during the import process (select plot) or by using the
commands

AND THEN check that a few selected grains have the same euler angles as in the
acquisition system by clicking on these points with the data cursor (mouse over the
icons on top of the figure until you find it). Check these against the values from the
Bruker system. If either the map orientation or the Euler angles are not identical, you've
got a problem

[grandr...@gmail.com]

Another fun point, I found that our first copy of the Bruker software (Esprit) was using DIFFERENT x-y axes for the spatial information and for the Euler orientations.  In one case x was positive to the right, in the other positive to the left.  A somewhat questionable programming decision I feel.  It was changed in the next edition of the software, so if you did scans both before and after the update you had some surprises to sort out in your data.