Understanding the effect of grain boundary solute segregation on the creep behaviour of thermally stable nanocrystalline materials: a theoretical approach

In this work, we provide a theoretical framework to evaluate the beneficial effect of solute segregation on the creep behaviour of nanocrystalline materials. We choose copper as the model system and employ the Murdoch and Schuh model to identify Cu-3Zr as a binary system with high thermal stability in its nanocrystalline state. The effect of the segregation of Zr on the grain boundary diffusivity was evaluated using the Hondros and Henderson model. The effect of solute segregation on threshold stress for vacancy emission and absorption at the grain boundaries was evaluated using the Mohamed model. Using these in conjunction with the Bird Mukherjee Dorn equation for creep allowed us to compare the diffusional creep behaviour of nc copper and nc Cu-3Zr. The nc Cu-3Zr system with a grain size of 49 nm demonstrated a higher creep resistance compared to nc Cu bearing a similar grain size. However, the creep resistance of both systems was found to be significantly inferior when compared to the conventional coarse-grained Cu bearing a grain size of 1 mu m.