Determining Deformation, Recovery and Recrystallization Fractions from Orientation Imaging Microscopy (OIM) Data

Abstract

While orientation imaging microscopy (OIM) via automatic analysis of electron backscatter diffraction patterns (EBSPs) has become routine, methods for analyzing results obtained by OIM are still maturing. Interrogating the OIM data to distinguish between deformed, recovered and recrystallized material in a polycrystalline sample is one example. An advantage for using OIM data in such a case is that the corresponding textures can also be determined providing more information regarding these processes. This work reports on two different approaches for distinguishing between these structures from OIM data on a sample of partially recrystallized low-alloy steel.The first approach is, in a sense, patterned after that used in optical microscopy; where, deformed material can be identified because it is more deeply etched than recrystallized material. A similar approach Can be used in OIM by considering the quality of EBSPs. EBSPs from deformed material are more diffuse than patterns obtained from recovered or recrystallized material. At each measurement point in an OIM scan an image quality (IQ) parameter is determined for the corresponding EBSP. The IQ is mapped onto a gray scale and an image is formed from the OIM data as shown in Fig. 1. In this image the measurement points are shaded so that points with associated EBSPs of high IQ receive a lighter shade of gray than points with a lower IQ. The deformed regions can then be identified by the darker regions in the OIM map. However, this method has some drawbacks. The first is that the IQ parameter is not sensitive enough to distinguish recovered material from recrystallized material.