Atomistic investigation of the annihilation of non-screw dislocation dipoles in Al, Cu, Ni andγ-TiAl

Abstract

Annihilation of vacancy-type non-screw dipolar dislocations is studied with molecular dynamics in fcc metals Al, Cu and Ni, and intermetallic γ-TiAl. Contrary to common belief, dipoles do not simply disappear. Instead, they transform into a series of defects depending on their height, orientation and temperature. At low temperatures, hollow structures, reconstructed configurations and faulted dipoles are formed. At high temperatures, with the help of short-range diffusion, isolated or interconnected vacancy clusters and stacking-fault tetrahedra are formed within a simulation time of 1 ns. Employing saddle-point-search methods, the formation of the above by-products is explained by accelerated diffusion paths along the dipole cores.

Autonomous basin climbing method with sampling of multiple transition pathways: application to anisotropic diffusion of point defects in hcp Zr

“…Therefore, such a breadthfirst search algorithm can easily become very expensive computationally. For example, in a recent study on the annihilation of a dislocation-dipole [22], Wang et al showed that the ART could not drive the system to the final state due to the 'very high computational load', and had to employ the ABC method to observe the dipole dissociation processes.…”

“…Recently, Cao et al further optimized the ABC method by introducing a self-learning algorithm [24], which can significantly reduce the computational cost. The implementation of the ABC algorithm is technically straightforward, and has been demonstrated to accurately capture the mechanism and kinetics of a series of unit processes, including the unfaulting of a self-interstitial atom (SIA) cluster in bcc Fe [25], the structure of a vacancy cluster in fcc Al [26], and the dislocation motion and structure [22,27] and interaction of dislocation with obstacles in both hcp Zr and bcc Fe [28,29]. However, when there are multiple competitive processes simultaneously, because of the 1D nature of the system evolution, the original ABC method overestimates the system evolution time [30][31][32].…”

Atomistic modeling at experimental strain rates and timescales

“…However, the additional computational expense entailed in cataloging multiple transition pathways can be prohibitive. For example, in recent studies of the annihilation of dislocation dipoles, the ART method was unable to complete the simulations, while ABC was able to observe the dislocation dissociation processes [74,75]. These issues again illustrate the need for more efficient ways to perform ABC-based explorations of the PES.…”

Abnormal Strain Rate Sensitivity Driven by a Unit Dislocation-Obstacle Interaction in bcc Fe

“…We would like to stress that although the present study focuses on the non-monotonic variation of CRSS in a BCC Fe system, the underlying principle-namely the complex interplay between thermal activation and mechanical loading-is rather general and applicable to many different materials. For example, it has been found in a large variety of materials (including Al, Cu, Ni, Zr, and intermetallic γ-TiAl) [16,17,36] that the microstructural evolutions of dislocations can be qualitatively different at different timescales. And the transitions between various mechanisms have been viewed as an underlying competition of strain rate and thermal activation, corroborating the spirit of the present study.…”