A comparison of grain size determination by light microscopy and EBSD analysis

The characterization and measurement of grain structures is of great importance to materials scientists because not only does grain size strongly affect the mechanical properties, but it also has an influence on physical properties, surface properties and phase transformations [1]. The ability to locate the grain boundaries in materials is critical for a wide number of applications, e.g. process control and property optimization. The mechanical and physical properties of metallic materials are frequently related to grain size, e.g. via the Hall-Petch relationship where strength is inversely dependent on the square root of grain size [2]. The sizes and shapes of grains are generally determined through optical or scanning electron microscopy of etched samples. Recent developments in the use of electron backscattered diffraction (EBSD) have made it an excellent tool for quantitative metallography. In addition to grain size determination, there are a number of important microstructural parameters available from EBSD not obtainable from conventional methods of grain characterization, in particular parameters relating to the grain orientations and boundary characters [3,4,5,6,7]. In most cases, it is assumed that the microstructure features, especially the grain size obtained from light microscopy and EBSD are the same. However, there is very little information available in literature related to the