Issue with merging grains in a twinning analysis

[apedgaon]

Hi,

I am trying to compute twin area fractions based on the example provided in the MTEX documentation. There is a step in which grains are merged across the twin boundaries. In my specific case, I am observing grains with very different orientations merge. I tried setting thresholds but couldn't avoid it. Can someone help with this?

disc.zip

[zmichels]

What about a slightly different approach?

%% Setup

% load data
ebsd = EBSD.load('c3p1.ctf', 'convertSpatial2EulerReferenceFrame');

% phase info
phase = 'Ti-Hex';
cs = ebsd(phase).CS;


%% Compute grains
grains = calcGrains(ebsd);

figure,
plot(ebsd, ebsd.rotations.angle./degree, 'figSize', 'huge')
hold on
plot(grains.boundary, 'LineWidth',2)
mtexColorMap(cool)
hold off
saveas(gcf, 'initialGrains.png')

%% all boundaries
gB = grains.boundary;

%% Ti-Ti boundaries
gbTi = gB(phase,phase);

%% boundary misorientations
gbMori = gbTi.misorientation.project2FundamentalRegion;

%% Dominant boundary-misorientation axis
moriAxDens = calcDensity(gbMori.axis, 'halfwidth',5*degree);
[~,maxMoriAx] = max(moriAxDens);

figure,
scatter(maxMoriAx,'MarkerSize',10,'MarkerFaceColor','k','MarkerEdgeColor','k','fundamentalRegion');

%% grain boundary indices with axis near maxMoriAx
gbMoriInd = angle(gbMori.axis, maxMoriAx)<2*degree;

%% twin bounadries?
isTwinning = gbMoriInd; 
twinBoundary = gbTi(isTwinning);

% plot the twinning boundaries
figure
plot(twinBoundary,'linecolor','k','linewidth',2,'displayName','twin boundary', 'figSize', 'huge')


%% try merging
[mergedGrains,parentId] = merge(grains,twinBoundary);

% plot the merged grains
figure
plot(ebsd(phase), ebsd(phase).rotations.angle./degree, 'figSize', 'huge')
mtexColorMap(cool)
hold on
plot(mergedGrains.boundary,'linecolor','k','linewidth',2,'linestyle','-',...
  'displayName','merged grains', 'figSize','huge')
hold off
saveas(gcf, 'mergedGrains.png')

[apedgaon]

@zmichels I'm sorry, but I don't think this resolved the issue. This is just another approach to identifying the twin boundaries, but the merging process still merges grains of very different orientations along twin boundaries. You can locate a few in your merged grain plot on the bottom right.

This leads to an incorrect twin area since it marks some grains as twins because of orientation change at an unidentified grain boundary inside the merged grain.

[zmichels]

makes sense.
what do you ultimately need to compute from the merged grainset?

[apedgaon]

@zmichels I am trying to compute twin area fraction by merging grains based on the example provided in https://mtex-toolbox.github.io/GrainMerge.html. Check my Matlab script originally attached.

This works well whenever merging grains goes correctly but if merging is incorrect then it identifies some grains as twins and gives incorrect area of twin.