Questions about the defineORs using ORTools-Example-3

[maohonghua]

Dear all,
Sorry to bother you. I am a MTEX and ORTools beginner and currently use the latest developer version of ORTools , MTEX v5.11.2 and MATLAB R2024b.
When I fit the two peaks, the orientation relationship results are not consistent with the expected.

job{1}
ans = parentGrainReconstructor
 
 phase   mineral  symmetry  grains  area   reconstructed
 parent  Beta     432       428     0.23%  0%           
 child   Alpha    622       43395   100%                
 
 OR: (103.1°,37.3°,255.2°)
   p2c fit: 12°, 12°, 13°, 13° (quintiles)
   c2c fit: 3.9°, 5.1°, 7.3°, 8.2° (quintiles)
   closest ideal OR: (3-3-1) || (1-10-1)   [110] || [14-5-3] fit: 0.68°`

job{2}
ans = parentGrainReconstructor
 
 phase   mineral  symmetry  grains  area   reconstructed
 parent  Beta     432       428     0.23%  0%           
 child   Alpha    622       43395   100%                
 
 OR: (91°,45.8°,284.3°)
   p2c fit: 11°, 11°, 11°, 12° (quintiles)
   c2c fit: 4.7°, 7.3°, 8.2°, 9.7° (quintiles)
   closest ideal OR: (101) || (41-50)   [010] || [-46-21] fit: 0.41°

This is not the same orientation as I expected.
% - OR1: (110)_beta||(1000)_alpha [1-11]_beta||[-12-10]_alpha
% - OR2: (11-1)_beta||(-1-100)_alpha [0-1-1]_beta||[000-3]_alpha
I want to know where the problem lies.
Any help or guidance would be greatly appreciated!

Best regards,
Honghua Mao

[AzdiarGazder]

Hi @maohonghua,

Thank you for reaching out.
As always, it is never a bother - we are happy to help out.

1. I would advise you to please go through the tutorial videos associated with each example.
   This will help improve your understanding of how MTEX and ORTools work.
   Videos for each example can be found on the ORTools landing page.
   Simply click on the triangle associated with each example to find the link to its tutorial video.
   For example, the tutorial video for Example 3 is located here.

2. The peak fitter does not have any beforehand knowledge of ORs "you expect".
   When you use the peak fitter, it is simply finding the OR corresponding to the peak in the misorientation histogram distribution.
   In all likelihood, and because of the thermo-mechanical history of your sample, the peak(s) in the misorientation histogram distribution will not correspond to any mathematically perfect rational ORs.
   It also follows that because this irrational OR corresponding to the peak in the misorientation histogram distribution is calculated from the EBSD map data - it is a relatively better starting guess for parent grain reconstruction than a rational OR.

3. On the other hand, if you do not want to use the irrational OR from the peak fitter as your starting guess, then do not use the peak fitter. In this case, you will need to define the starting guess OR manually using either of the following 2 methods.

Method 1

% define the parent symmetry for beta
csParent = crystalSymmetry('m-3m', [3.32 3.32 3.32], 'mineral', 'beta');
% define the child symmetry for alpha
csChild = crystalSymmetry('6/mmm', [2.545 2.545 4.14], 'X||a*', 'Y||b', 'Z||c', 'mineral', 'alpha');

% describe the parent beta to child alpha Burgers orientation relationship
% parent beta plane and direction
pPlane = Miller({1,1,0},csParent ,'hkl');
pDirection = Miller({1,-1,1},csParent ,'uvw');
% child alpha plane and direction
cPlane = Miller({0,0,0,1},csChild ,'HKIL');
cDirection = Miller({1,1,-2,0},csChild ,'UVTW');
% define the Burgers OR
job.p2c = orientation.map(pPlane, cPlane, pDirection, cDirection);

Method 2

job.p2c = orientation.Burgers(job.csParent, job.csChild);

Regardless of whether your starting guess OR is from the peak fitter, or if you have manually defined it, you will see that after the refinement step is completed, the best-fit OR is still an irrational OR.
Irrational ORs possess a small deviation from the perfectly parallel set of parent-child planes and directions.

**Lastly, and importantly, if an explanation from the maintainers resolves your issue, please press the "Mark as answer" button on the appropriate response. Your assistance in this regard enables us to close discussions as complete. **

Hope this helps.

Warm regards,
Azdi