Large-scale molecular dynamics simulations reveal length-dependent dislocation mobilities in Fe-Cr-Ni austenitic stainless steel

We present a systematic study of edge dislocation mobility in random, austenitic Fe_0.7Ni_0.11Cr_0.19 alloys over a range of temperatures, stresses, and dislocation line lengths. Our results reveal that, below a minimum dislocation line length, solid solution strengthening is intrinsically line-length-dependent. Below the minimum length, the dislocation mobility is reduced and strengthening is increased. We show that the minimum line length is both stress- and temperature-dependent, and anticipate that it is also sensitive to solute type and concentration. Furthermore, analysis of the dislocation line configurations in the solute drag regime reveals that dislocation lines adopt large amplitude (>50b), wavy configurations during glide. Our findings present evidence that the characteristic segment length invoked by the recent solute strengthening model of Leyson and Curtin (LC) is a real feature of dislocation-solute interactions. Using solute, phonon, and wave-speed-induced drag parameters extracted from the MD data, we develop a kinetic Monte Carlo (kMC) model inspired by the LC model that rationalizes the length dependence of the mobility. The kMC model cannot reproduce the large bowing that is observed in the MD simulations, however, unless the dislocation line tension adopts unphysically small values.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.