Correction of step size dependency in local misorientation obtained by EBSD measurements: Introducing equidistant local misorientation

Abstract

The local misorientation, known as KAM, is affected by both the step size (representing the spacing of measurement points applied in orientation measurements) and the point distance (indicating the distance between the points used in the misorientation calculation). The point distance can be increased by selecting surrounding points that are far from the target point. This study proposed the concept of an equidistant local misorientation, for which surrounding points at the same point distance from the target point were selected to calculate misorientation. An arbitrary point distance can be set for the equidistant local misorientation regardless of the step size. The changes in equidistant local misorientation for various point distances were calculated for the crystal orientation datasets obtained with different step sizes and measurement grids (square or hexagonal) using Type 316 stainless steel specimens, in which plastic strain of about 5 % was induced. It was shown that the equidistant local misorientation was identical regardless of the step size and measurement grid when the same point distance was used. Then, it was concluded that the difference in the local misorientation which emanated from the difference in step size could be corrected by employing the equidistant local misorientation. Increasing the point distance improved the signal-to-noise (S/N) ratio in the mapping data of the equidistant local misorientation. However, the results suggested that the maximum point distance for enhancing the S/N ratio should be within 30 % of the average grain size. On the other hand, decreasing the step size by keeping the point distance constant was found not to improve the S/N ratio, while it enhanced the spatial resolution of the mapping data.