Three-dimensional grain growth in pure iron. Part I. statistics on the grain level

Abstract

Grain evolution in pure iron is determined in three dimensions using diffraction contrast tomography at a synchrotron source. During annealing for 75 min at 800∘C, the evolution of initially 1327 grains is quantified as a function of 15 time-steps. A comprehensive statistical analysis is provided based on the equivalent radius, the number of faces and the mean width parameters of the grains. We introduce analytical relations between these parameters, validate them, and discuss their physical meaning. While the sample is fully recrystallized, the growth is found not to be self-similar, as evidenced in changes in the distributions of normalized grain size and number of faces per grain. More importantly, a strong decrease in the slope of the growth rate over the mean width of grain faces is observed, indicating a slowdown of grain growth. The data is used to determine the applicability of the isotropic MacPherson-Srolovitz theory to an anisotropic material such as iron. Geometrical properties that are averaged over the entire grain ensemble are well described by the model, but the properties and evolution of the individual grains exhibit substantial scatter.