Experimental and simulation study of grain boundaries in UO2

Abstract

EBSD measurements performed on polycrystalline UO2 samples were analyzed to obtain the linear fraction distribution of grain boundaries as a function of their Coincidence Site Lattice (CSL) indexes. In parallel, molecular dynamics simulations of 26 CSL grain boundaries were performed to calculate their formation energies using four different empirical potentials. Comparing calculated formation energies and measured linear fractions allowed us to select the best suited empirical potential for the study of grain boundaries and to evidence a decrease in the formation energy of a given grain boundary when its length fraction increases. Cleavage energies were calculated using the selected potential and the toughness of a grain boundary was estimated, since this property corresponds to the energy needed to open it. An interesting relation is observed: the cleavage energy seems to decrease when the misorientation angle of the boundary increases. Finally, a first step towards the study of non-CSL (i.e. general) grain boundaries was taken by simulating three semi-general grain boundaries built by sticking two halves of CSL boundaries.