Grain size characterization in metallic alloys using different microscopy and post-processing techniques

In this work, an image analysis procedure which enables an estimation of grain size distribution from optical and scanning electron micrographs is detailed. Two applicative cases (a face centered cubic austenitic stainless steel and a hexagonal close packed zirconium alloy, both with fully recrystallized equiaxed microstructure) are considered. Grain size definition is discussed both in terms of mean grain size and of grain size distribution. Classical methodologies as well as standardized definitions are recalled and compared to each other. Results obtained by electron backscattered diffraction analysis are compared to the ones obtained after image analysis based on backscattered electron or optical micrographs. The effect of data processing parameters on grain size results is also examined. Image analysis based on optical or scanning electron micrographs proves to be suitable to obtain accurate grain size distribution information with shorter acquisition and processing times compared to EBSD orientation mapping of the same analyzed area.