Atomic-scale investigation of creep behavior and deformation mechanism in nanocrystalline FeCrAl alloys

FeCrAl alloys have been proposed as nuclear fuel cladding materials in hope of offering great potential in accident tolerance for light water reactors. However, only a limited amount of data has been published on their creep properties. This work aims to provide an atomic-scale insight into the creep behavior and deformation mechanism for nanocrystalline FeCrAl alloys, using molecular dynamics method. Both primary and steady state creeps are observed in all creep curves, and tertiary creep occurs at stresses above 2.5 GPa in the time period of the present simulation. As stress increases, the creep mechanism transits from Coble creep to grain boundary sliding, and then to the synergy of grain boundary sliding and dislocation creep. The turning points are about 0.8 GPa and 1.8 GPa, respectively. The dislocation motions are controlled by viscous gliding at low temperature, and then by climbing when temperature exceeds 1000 K. Moreover, the grain size and alloy composition have little impact on the transition of creep mechanism within the present research scope. The proposed creep mechanisms are further analyzed not only from the comparison between activation energies for diffusion and creep, but also from the representative atomic snapshots.