Abstract
Cu-Nb layered nanocomposite system can be considered as a prototype system to investigate stability of the fcc-bcc semicoherent metallic interfaces. Theoretical simulations based on density functional theory have been performed in order to investigate the stability of different defects in such interfaces. The calculations find the interfacial misfit dislocation intersections as the preferred site for defects including a vacancy, He-interstitial, and a vacancy-He complex in good agreement with previous works. Our results suggest that the presence of a metallic vacancy may act as a sink for defect and favour the migration of He interstitials leading to their aggregation at the interface. The potential capability of the vacancy to accommodate He atoms was also predicted with a higher affinity towards Nb. This aggregation of He atoms is driven by local density of electron and strain in a region in the neighbourhood of Nb. Finally, we propose a plausible picture of defect energetics in the vicinity of the interface based on the Voronoi volume and Bader’s charge analysis. This analysis may replace the conventional methods used for surface energetics mapping which are extremely tedious for such large systems.
Highlights
The face-centered cubic and the body-centered cubic semicoherent layered metallic nanocomposite systems have engrossed as a viable structural material for the generation of nuclear reactors[1,2,3]
The prominent trapping exerted by the Cu-Nb interface on metallic vacancies and He interstitial atoms were studied with the help of metallic vacancy/He interstitial formation energy and Density functional theory (DFT)-based defect migration barrier calculations
The first step in our procedure consists of the validation of the computational DFT parameters in order to show that the obtained results are not artifacts of the restrictions implemented in our simulations
Summary
The face-centered cubic (fcc) and the body-centered cubic (bcc) semicoherent layered metallic nanocomposite systems have engrossed as a viable structural material for the generation of nuclear reactors[1,2,3]. Demkowicz’s group constructed different DFT-based embedded atom method (EAM) potentials in order to perform extensive MD calculations by considering Cu-Nb as a prototype fcc-bcc nanocomposite system They studied the interface energetics, structure, mechanical properties as well as clustering and migration behavior of vacancies or He interstitials[22,23,24,25,26]. The necessity of a large simulation cell to capture the topology of the non-coherent interface and strain field generated near the interface was the major challenge to perform DFT based calculation on Cu-Nb layered system, which was nicely untangled by Metasanurk et al with the introduction of a quasi unit cell of reasonable size[29] They performed first-principles simulations on the metallic vacancy and self-interstitial formation energy in the Cu-Nb system, showing the most stable sites at the misfit dislocation intersection (MDI), i.e. Cu/Nb atom sites at the top of the other species. Inspired by the study performed by Choudhury et al.[32], we have performed Voronoi volume and Bader charge analysis to understand the point defect energetics at the interface of the fcc-bcc semicoherent metallic system
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