Difference in grain area calculated by Mtex and OIM analysis

[King Peter]

Dear all

I am trying to calculate the average grain size of my ebsd data. But there is a large difference between the results from Mtex and TSL OIM Analysis. Could you kindly help me?

{

% crystal symmetry

CS = {... 

  'notIndexed',...

  crystalSymmetry('m-3m', [3.56 3.56 3.56], 'mineral', 'Nickel', 'color', 'light blue')};

% plotting convention

setMTEXpref('xAxisDirection','north');

setMTEXpref('zAxisDirection','outOfPlane');

%% Specify File Names

% path to files

pname = 'D:\';

% which files to be imported

fname = [pname '\try.osc'];

%% Import the Data

% create an EBSD variable containing the data

ebsd = EBSD.load(fname,CS,'interface','osc',...

  'convertEuler2SpatialReferenceFrame','setting 2');

cs=crystalSymmetry('m-3m'); % for fcc

oM=ipfHSVKey(cs);  % Or: oM=ipfHSVKey(ebsd('Nickel')); 

% oM=ipfTSLKey(cs);% oM=ipfTSLKey(ebsd('Nickel'));% plot(oM)

%setting the inverse pole figure direction

oM.inversePoleFigureDirection=zvector;

% smooth

ebsd=ebsd('indexed'); % this removes all not indexed data

grains=calcGrains(ebsd, 'threshold',15*degree); 

grains=smooth(grains,5); %smooth the grains

plot(ebsd('Nickel'),oM.orientation2color(ebsd('Nickel').orientations), 'micronbar', 'on')

dlmwrite('try.dat',grains.area)

average_grainsize=mean(grains.equivalentRadius*2)

average_grainsize =

    2.1442

}

Thank you

[Rüdiger Kilian]

Hi,

comparing the images you provided, it looks like the segmentation is not identical. It seems you have some more smaller grains in your OIM derived image. The numeric average of grain radii isn't a good representation for the volume/area and very susceptible to the number of tiny grains, hence any sort of filtering.

There might be some other reasons for differing results: In mtex, you decided to compute grains only on an indexed subset, hence all non-existent area -if any-  will be attributed to grain areas. I have no idea how this is handled in OIM, but as far as I can see, your map looks quite complete.

Another very minor alteration of the grain area will also originate from smoothing grains in mtex.

So, unless your grain boundaries do not perfectly agree, I'd be surprised if you'd get identical results.

I hope this help.

Cheers,

Rüdiger

[King Peter]

Thank you for your kind reply. It is very helpful.
I calculated the diameter by area fraction method based on the grain
area data from Mtex. The result is 15.3. The OIM diameter is 12.25.

Thank you again.

'Rüdiger Kilian' via MTEX <mtex...@googlegroups.com> 于2019年12月9日周一 下午10:23写道：

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[Rüdiger Kilian]

The difference is for one and the same grain which apparently exactly overlaps?
Cheers,
Rüdiger

[King Peter]

No. The difference is for the average grain size.

I am using the following equation.

average grain size=sum((grain area(i)/total area)*2*(grain area(i)/3.14)^0.5)

在 2019年12月10日星期二 UTC+9下午6:06:57，Rüdiger Kilian写道：

[Rüdiger Kilian]

In that case, it's not suprising that you get different results.
Cheers,
Rüdiger