Size effects in stress propagation and dynamics of dislocations: Fe-Ni-Cr steel

摘要

Movement of line dislocations in fcc steel 310S is found to depend on the size of nanometer sized structures, based on modeling within molecular dynamics (MD). The effect is attributed to time (and size) dependencies of pressure propagation into the medium interior. The observation is crucial in interpreting any MD studies of pressure effects since these are governed by time-dependent internal virial stresses. In particular, velocity of dislocations scales better with value of local internal shear component of virial stress S ( xy ) than with external shear pressure applied. Dynamics of stress penetration is described well within the model of damped harmonic oscillator, where characteristic oscillation frequency depends on number of crystallographic layers in direction along the wave propagation while the speed of stress propagation is the speed of sound. The minimal stress required for dislocation movement (Peierls stress) is determined to be 0.75 GPa. Pressure and temperature effects on dislocation movement are systematically investigated.