Evolution pattern of collision cascades in bcc V with different grain boundary structures: an atomic scale study

Abstract

In this paper, by means of atomic-scale simulations, we investigate modifications of the evolution pattern of collision cascades in bcc vanadium (V) with different grain boundary (GB) structures on picosecond (ps) timescale. In primary damage state, in agreement with previous results of bcc and fcc bi-crystals, we find that the GBs in V are biased towards interstitials. The biased absorption of interstitials over vacancies reduces the in-cascade annihilation of vacancy-interstitial pairs and leads to aggregation of more number of vacancies in the grains interiors. The sessile vacancies accumulate in the bulk and form immobile vacancy clusters; in contrast, the glissile interstitials disperse in the damage zone and mostly diffuse in the form of single self-interstitial atoms (SIAs)/di-interstitials towards the GB region. Moreover, meanwhile, as we discuss the mechanisms that reduce (or increase) the concentration of defects in bi-crystal structures on picosecond timescale, we study the energetics of defects in close vicinity of pristine GBs, as an alternative driving force that facilitates formation and accumulation of defects in the GB regions. Finally, in a prolonged irradiation, we examine stability and sink properties of the damaged GBs. The results reveal that, irrespective of GB structure, the presence of grain boundaries leads to aggregation of more number of vacancies in the grain interiors in continuous bombardment. Overall, based on the results obtained in the primary damage event and the prolonged irradiation, we conclude that the GBs in bcc V act as efficient defect sinks on the simulated time frame.

Keywords:

• Primary cascade
• prolonged irradiation
• grain boundary
• atomic scale simulations