Temperature and composition dependent screw dislocation mobility in austenitic stainless steels from large-scale molecular dynamics

Kevin Chu,Ting Zhu,David L Mcdowell,Xiaowang Zhou,Michael E Foster,Ryan B Sills

doi:10.1038/s41524-020-00452-x

Abstract

Extensive molecular dynamics simulations are performed to determine screw dislocation mobility in austenitic Fe0.7NixCr0.3-x stainless steels as a function of temperature ranging from 100 to 1300 K, resolved shear stress from 30 to 140 MPa, and Ni composition from 0.0 to 30.0 at%. These mobility data are fitted to a linear mobility law with a nonzero stress offset, referred to as the threshold stress. We find that both the linear drag coefficient and the threshold stress increase with Ni composition. The drag coefficient increases with temperature, whereas the threshold stress decreases with temperature. Based on these calculations, we determine fitting functions for the linear solute drag coefficient as a function of temperature and composition. The mobility laws determined in this study may serve to inform dislocation dynamics simulations pertinent to dislocation network evolution at elevated temperatures for a wide composition range of austenitic stainless steels.

Highlights

The use of austenitic stainless steels such as 304 and 316 is ubiquitous across applications that demand strength and corrosion resistance at moderate cost
Discrete dislocation dynamics (DDD) is one such method that seeks to describe mesoscale phenomena by evolving microstructures using a set of physics-based heuristic rules[6,7,8]
Dislocation velocities are extracted from molecular dynamics (MD) simulations run for fcc Fe0.7NixCr0.3−x at seven compositions, eight stresses (τ = 30, 40, 60, 80, 90, 100, 120, and 140 MPa), and seven temperatures (T = 100, 300, 500, 700, 900, 1100, and 1300 K)

Summary

INTRODUCTION

The use of austenitic stainless steels such as 304 and 316 is ubiquitous across applications that demand strength and corrosion resistance at moderate cost. The presence of solute–dislocation and solute–solute interactions[21] induces elastic misfit strain fields[29,30], presenting non-negligible pinning barriers[16] that must be overcome to initiate dislocation glide This threshold stress controls the material’s resistance to dislocation glide at low temperatures, where the kinetics of thermally activated obstacle bypass is slow. This suggests a linear dependence on composition This form was derived and validated against a binary alloy within a limited temperature range; the presence of multiple solute atoms may require additional terms or an alternate form altogether, if their relative misfit volumes differ[30]. To the best of our knowledge, the current work offers the most comprehensive analysis to date across both temperature and composition variables in the Fe0.7NixCr0.3−x austenitic stainless-steel alloy system

RESULTS AND DISCUSSION

METHODS

10 COMPETING INTERESTS