The role of grain boundary structure in stress-induced phase transformation in UO2

Recently, we reported on a phase transformation in UO2 aided by the presence of high-energy amorphous grain boundaries (Desai and Uberuaga 2009 Scr. Mater. 60 878). Here, we examine the role that the structure of the grain boundary plays in aiding this phase transformation. By examining three bicrystalline systems with different types of grain boundaries (amorphous, Sigma 5 tilt and Sigma 5 twist), we study the influence on the phase transformation behavior by the critical applied stress to induce the phase transformation, the effects of grain size and the grain boundary type. We find that there is a critical applied stress below which the phase transformation does not occur, and that the phase transformation occurs more readily in systems with smaller grain sizes. Finally, we observe a weak dependence on the applied stress to cause the phase transformation with the grain boundary energy.