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

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.

The effect of local chemical ordering on dislocation activity in multi-principle element alloys: a three-dimensional discrete dislocation dynamics study

“…Thus, the 3D DDD simulations show that the large increase in flow stress observed in experiments [13] by replacing Mn with Pd in the CrMnFeCoNi MPEA can be explained entirely by the higher misfit of Pd atoms rather than nanoscale composition fluctuation. In addition to using a pure Ni mobility law, these conclusions hold also for the response of the CrFeCoNiPd effective average alloy and the 100 nm lamella LCO simulation using a concentration-dependent mobility law for FeNiCr-based stainless steels recently published in [34] (see Appendix A).…”

“…For simplicity, the simulations shown in this study incorporate a dislocation mobility law for pure Nickel. However, the conclusions of the work do not change when using a concentration-dependent dislocation mobility law for FeNiCr-based stainless steels obtained by molecular dynamics simulations [34] (see Appendix A for more details).…”

The interplay of local chemistry and plasticity in controlling microstructure formation during laser powder bed fusion of metals

“…where µ(T ) is the shear modulus, ν(T ) the Poisson ratio, b is the Burgers vector magnitude, f 1 (w c ) = 0.35 and f 2 (w c ) = 5.70 are core coefficients according to literature [35], and α = 0.5 is the isotropic line-tension parameter close to previous assumptions for screw dislocations [40].…”

“…The effective nodal force f eff is related to nodal velocities v by a dislocation mobility law in the form of v = M (f eff ), where M is a mobility function whose arguments contain the effective nodal force as well as a temperature-dependent dislocation drag coefficient B(T ). For the drag coefficient we apply an estimation for stainless steels which has recently been obtained from molecular dynamics (MD) simulations for Fe 0.7 Ni x Cr 0.3−x [40], where we use x = 0.15.…”

“…In order to investigate this dependency, isothermal 3D DDD simulations have been conducted at 1300K, 1100K, 900K and 700K. We account for a physically meaningful representation of the dislocation evolution in 316L SS via a temperature-dependent dislocation mobility law adapted from molecular dynamics (MD) simulations [40] and a recently developed model for the local composition-dependent critical resolved shear stress (CRSS) [37]. The experimentally observed 100 -aligned and periodic spatial variation in chemical composition (local Mo and Cr enrichment) adapted from [13,14,42] are explicitly incorporated in the simulations, see Fig.…”