Atomistic simulation for deforming complex alloys with application toward TWIP steel and associated physical insights

Abstract

A B S T R A C TThe interest in promoting deformation twinning for plasticity is mounting for advanced materials. In contrast to disordered grain boundaries, highly organized twin boundaries are beneficial to promoting strength-ductility combination. Twinning deformation typically involves the kinetics of stacking faults, its interplay with dislocations, as well as the interactions between dislocations and twin boundaries. While the latter has been intensively studied, the dynamics of stacking faults has been rarely touched upon. In this work, we report new physical insights on the stacking fault dynamics in twin induced plasticity (TWIP) steels. The atomistic simulation is made possible by a newly introduced approach: meta-atom molecular dynamics simulation. The simulation suggests that the stacking fault interactions are dominated by dislocation reactions that take place spontaneously, different from the existing mechanisms. Whether to generate a single stacking fault, or a twinning partial and a trailing partial dislocation, depends upon a unique parameter, namely the stacking fault energy. The latter in turn determines the deformation twinning characteristics. The complex twin-slip and twin-dislocation interactions demonstrate the dual role of deformation twins as both the dislocation barrier and dislocation storage. This duality contributes to the high strength and high ductility of TWIP steels.

Atomistic modeling and analysis of hydride phase transformation in palladium nanoparticles

“…Therefore, the four regions have the features of: (1) a perfect FCC lattice, (2) an intrinsic stacking fault, (3) an extrinsic stacking fault, and (4) a three-layer twin, respectively. This type of stacking fault structure has been observed previously in MD simulations of mechanical twinning (e. g., in aluminum [57] and steel [58]). Nonetheless, our results reveal that, this twinning process can also be driven by the high residual stress due to phase transformation in chemical reactions (specifically, hydrogenation of Pd).…”

Effect of pre-existing defects in the parent fcc phase on atomistic mechanisms during the martensitic transformation in pure Fe: A molecular dynamics study

“…During heating the crystal structure changes from bcc-to-fcc at 1300 K. During simulations with different initial velocities, fcc phase attained three different arrangements of the defects at 1300 K which will be discussed below in detail. The bcc-to-fcc transformation during heating has been discussed in the literature for Fe alloys by MD simulations [20,27,33,34]. The fcc structure is then cooled from 1600 K to 50 K. The cooling rate used is 1 K/ps.…”

A general perspective of Fe–Mn–Al–C steels

“… Molecular dynamics simulations can be very useful to understand the interactions between stacking faults and twins, or dislocations and twins. Recent results elucidate these issues in Fe-Mn-C steels [353]. For this reason, this tool can be used to study and gain a depth insight about the interactions between martensite and dislocations, dislocations and κ-carbides, and to study the effect of variables such as the strain rate, the chemical composition and the test temperature on phase transformations in Fe-Mn-Al-C steels from an atomistic point of view.…”