Irrational orientation relationship derived from rational orientation relationships using EBSD data

The determination of the orientation relationship (OR) between alpha-Fe matrix (bcc) and gamma-Fe precipitates (fcc) is discussed using orientation data collected by electron backscatter diffraction (EBSD). The comparatively low accuracy of EBSD is compensated by the high number of measurements which gives a general statement regarding to the mean OR existing in a sample. The representation and discussion is realized on a part of the Bain zone in a {001} pole figure. A discussion of some selected rational OR which are commonly used for the phase boundary characterization between a and gamma shows that the pole figures describing a transformation from gamma -> alpha are different to those for alpha -> gamma. A technique is proposed based on at least three misorientation angles between the experimental OR to the rational OR's as reference. For the misorientation angle distribution a refinement is applied to extract the mean values. They are used to detect the mean OR, what is also possible for only a few or even a single precipitate if the number of measurements describing the phase boundary is sufficiently high. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.