Statistical distribution of spontaneous recombination radii of Frenkel pairs in FCC and BCC metals

The recombination radius of Frenkel pairs induced by incident high-energy particles represents a critical determinant of irradiation-induced microstructure evolution. A better understanding of the atomistic processes controlling recombination can help us determine more accurately the average recombination radius, an essential input parameter of mesoscale models of radiation damage evolution. This work used the kinetic activation relaxation technique—an off-lattice, self-learning kinetic Monte Carlo algorithm in conjunction with molecular dynamics simulations—to study the statistical distribution of the recombination radii in six FCC (nickel, copper, silver, gold, palladium, and platinum) and one BCC (iron) metals. We found that recombination can occur from the 2 ^nd nearest neighbor site to as far as the 15 ^th neighbor site. Long-range recombination is realized via crowdion formation along <110> directions. Vacancies were found to diminish the recombination energy barrier, yet no correlation was found between energy barriers and the average recombination radius. Instead, the average recombination radius increases linearly with elastic constants. Although the atomic displacement fields near self-interstitials are identical in different metals, metals with higher elastic constants exhibit larger local stresses and broader stress distribution, facilitating long-range recombination. Similarly, hydrostatic pressure enhances the average recombination radius by rising elastic constants of the compressed structure. Thus, it is the elastic constants that determine the average recombination radius, not energy barriers.