OIM Analysis

Orientation Image Microscopy (OIM) Anaysis software is used to analyze Electron Backscatter Diffraction (EBSD) data. The data collection and analysis software is a commercial package from EDAX-TSL. One important feature of the analysis is grain size.

Grain Size Analysis

Grain Size Parameters

First off the data can be understood as pixels. Each pixel has an orientation and physical scale associated with it. In order to define a grain, a grain tolerance angle needs to be specified. This angle is the allowable misorientation between neighboring pixels. Secondly in order to avoid counting noise in the data as grains, a minimum grain size is also specified.

The defaults are 5 degrees and 2 microns respectively.

Misorientation

Misorientation refers to the rotation required to bring Grain A into coincidence with Grain B. The description can be made as an axis-angle pair, Rodrigues Vector, or with Bunger-Euler angles. Most times, only the angle from the axis-angle pair is considered, and the minimum angle (multiple axis-angle pairs can accomplish AB coincidence) is used.

Grain Size Formula

The default grain size calculation is to insert the area of the grain into the equation for area of a circle. From this the equivalent diameter can be found. Insert formula here

ASTM Grain Size

Insert formula here

Grain Shape

The most you can do here is treating the grain as an oval. The major and minor axes can be calculated as the max and min chord lengths or through a least squares fit to the equation of an oval.

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References/Resources