Atomic simulation of phosphorus segregation in nickel grain boundaries and its impact on deformation mechanisms

The segregation behavior of phosphorus on the grain boundary (GB) structure and mechanical response has been studied in the Ni-P system. Fourteen twist and tilt bi-crystals have been selected from the Olmsted dataset. Then, hybrid Monte Carlo/Molecular dynamics simulations (MC/MD) are used to obtain the equilibrium GB at 300 K and 1000 K, respectively. The present study indicates that solute phosphorus dissolved in the nickel matrix is inhomogeneous segregated to all of the GBs. GB characters including GB free volume and energy are found to correlate with segregation. The participated phase with Ni3P composition was observed only at 1000 K and for the lower energy GBs. Furthermore, we performed simulations of tensile deformation for the GBs with and without segregation. The twist and tilt GBs initially exhibit linear and non-linear elasticity behavior, respectively. The twist GBs demonstrate an increased yield strength with the help of phosphorus segregation. Besides, the thermal annealing process at 1000 K promotes uniform segregation at GB, leading to further strength enhancement. Conversely, the strength is weakened in segregated tilt GBs. This work illustrates the relationships among composition, GB structure, and mechanical properties.