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Determination of grain size by EBSD - Report on a round robin measurement of equiaxed titanium.

Mingard, K P; Quested, P N; Peck, M S (2012) Determination of grain size by EBSD - Report on a round robin measurement of equiaxed titanium. NPL Report. MAT 56

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An interlaboratory exercise was carried out across 12 laboratories to measure the average grain size of a titanium metal sample with an approximate average grain size of 30 µm using Electron Backscatter Diffraction (EBSD). Participants were asked to follow the proposed draft International Standard, ISO DIS13067 "Microbeam analysis-Electron Backscatter Diffraction-Measurement of Grain Size and Distribution".

Of the initial results submitted the equivalent circle diameter values from 4 of the 12 laboratories reported differed significantly from the overall mean value. Causes of these differences were identified in three cases and corrections made for two after which a full statistical treatment of the data was then used to remove remaining outliers.

The average grain size calculated from equivalent circle diameter measurements gave a value approximately 10% greater than calculated using linear intercept measurements. The results showed much greater variation of the average between laboratories (reproducibility) than between several measurements made by a single laboratory (repeatability). The reproducibility limit for equivalent circle diameter measurements was about 80% greater than that for linear intercept measurements, probably because additional errors from calibration drift and tilt correction perpendicular to the tilt axis contribute only to the former method.

Sources of differences in results are discussed and it is concluded that the choice of smallest grain size to be included in the calculation of the average has the greatest effect on the reported values. Choice of a relatively large cut off size is likely to give the best agreement because the smallest grains can have a significant effect (disproportionate to the area they occupy) and are also the grains most likely to vary in number and size with the step size chosen, the quality of the data and/or the treatment of poorly indexed points.

Item Type: Report/Guide (NPL Report)
NPL Report No.: MAT 56
Keywords: EBSD, Grain size
Subjects: Advanced Materials
Advanced Materials > Microstructural Characterisation
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/5412

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