Atomic origins of dislocation pinning in oxide dispersion strengthened alloys

Recent developments in oxide dispersion strengthened (ODS) alloys have revealed significant improvements in creep and oxidation properties compared to their non-ODS counterparts. The mechanistic origin of such property improvements is not well understood, particularly with regards to creep performance where ODS alloys can exhibit significantly different responses compared to their non-ODS counterparts. Investigation of such effects through simulation has recently been enabled through the development of new computationally efficient charge transfer ionic potential for the Ni-O system. Using this newly developed capability, we performed molecular dynamics simulation to investigate the mechanism of creep strengthening in ODS alloys by simulating oxide-dislocation interactions. These simulations demonstrated that the bypass of the oxide is controlled by the direct dislocation-particle interaction at the oxide-metal interface, rather than repulsion of the dislocation as required for Orowan looping. Therefore, the dislocation interactions must be governed by effects acting on the dissociated dislocation core over the Ni-NiO interface. The ODS strengthening effect is likewise observed to be relatively insensitive to temperature variation, which is in line with experimental measurements demonstrating ODS strengthening at a wide range of temperatures. Finally, this improved understanding of the fundamental oxide strengthening mechanisms indicates that local structure at the metal-oxide interface is critical for strengthening of the ODS alloys.