Can the average particle section size in a metallographic plane be larger than the true average particle size in a three-dimensional microstructure?

Abstract

It is shown that the average particle section size observed in a metallographic plane can be larger or smaller than the true average particle size in the three-dimensional (3-D) microstructure. The ratio of the average particle section size in a representative metallographic plane to the true average particle size in the 3-D microstructure is linearly related to the square of the coefficient of variation (CV) of the size distribution function in the 3-D microstructure. For most of the size distributions encountered in material microstructures, the average particle section size in a metallographic plane is expected to be larger than the true average particle size in the 3-D microstructure. Experimental data on hollow spherical carbon particles in a polymer matrix composite are presented to illustrate the theoretical results.