Multiscale modeling of crowdion and vacancy defects in body-centered-cubic transition metals

Abstract

We investigate the structure and mobility of single self-interstitial atom and vacancy defects in bodycentered-cubic transition metals forming groups 5B ͑vanadium, niobium, and tantalum͒ and 6B ͑chromium, molybdenum, and tungsten͒ of the Periodic Table. Density-functional calculations show that in all these metals the axially symmetric ͗111͘ self-interstitial atom configuration has the lowest formation energy. In chromium, the difference between the energies of the ͗111͘ and the ͗110͘ self-interstitial configurations is very small, making the two structures almost degenerate. Local densities of states for the atoms forming the core of crowdion configurations exhibit systematic widening of the "local" d band and an upward shift of the antibonding peak. Using the information provided by electronic structure calculations, we derive a family of Finnis-Sinclair-type interatomic potentials for vanadium, niobium, tantalum, molybdenum, and tungsten. Using these potentials, we investigate the thermally activated migration of self-interstitial atom defects in tungsten. We rationalize the results of simulations using analytical solutions of the multistring Frenkel-Kontorova model describing nonlinear elastic interactions between a defect and phonon excitations. We find that the discreteness of the crystal lattice plays a dominant part in the picture of mobility of defects. We are also able to explain the origin of the non-Arrhenius diffusion of crowdions and to show that at elevated temperatures the diffusion coefficient varies linearly as a function of absolute temperature.

Comparison of molecular dynamics and binary collision approximation simulations for atom displacement analysis

“…It is known from experiments and simulations that individual ion impacts partially amorphize the crystalline structure [54,55,59]. …”

From materials development to their test in IFMIF: an overview

“…A substantial difference in the spatial distribution of SIAs was, however, found. They are diffusing further away from the cascade core with two of them [20,21], relative to results obtained with the third one [22], which was attributed to the lower migration energy of SIAs obtained with the former two potentials. These potentials also predict a too high melting temperature and a too high formation energy for the 1 1 0 SIAs.…”

“…A strong dependence on the interatomic potential describing the W-W interactions was found. For one of the potential [21] the lowest formation energy is achieved with the 1/2a o 1 1 1 {1 1 1} loop, while in the case of another potential [22] the 1/2a o 1 1 1 {1 1 1} loop for radii smaller than 2a o (0.63 nm, or about 20 SIAs) and the a o 1 0 0 {1 0 0} loop for larger sizes are favourable [23], which is in contradiction with experimental observations, though scarce. MD simulations of 10, 20 and 50 keV atomic displacement cascades at 10 and 523 K in pure tungsten were performed to assess the primary damage due to irradiation, with the dependence on the interatomic potential [24].…”

“…The microstructural features of irradiated tungsten were investigated using MD simulations and three different interatomic potentials [20][21][22]. With two of the most adequate potentials for defects [21,22] the lowest energy SIA in bcc tungsten appears to have a 1 1 1 structure [23].…”

“…With two of the most adequate potentials for defects [21,22] the lowest energy SIA in bcc tungsten appears to have a 1 1 1 structure [23]. Nanometric loops formed by SIA platelets were investigated as a function of their size to find the lowest energy configuration.…”