Theoretical study on the influence of Cr, Mo, and W alloying additions on the helium behavior in nickel

Abstract

In nuclear reactors, the helium (He) production and retention from intensity particle irradiation can degrade the physical and mechanical properties of Ni-based alloys. Understanding the fundamental behaviors of He in metals is a critical issue in the development of nuclear materials. In this research, the influence of Cr/Mo/W additions on the stability, migration, and clustering of He in face-centered cubic (fcc) nickel were systematically studied by using density functional theory (DFT). The formation and binding energies show that Cr and Mo/W atoms affect the occupying priority of tetrahedral interstitial He in Ni lattice. The interstitial He prefers to occupy the first nearest neighbor octahedral site with the presence of Cr, while it would locate far away from Mo/W addition. For He migration around alloying elements, the barrier of interstitial He in NiCr is slightly higher than that of pure Ni, while NiMo and NiW systems have a relatively lower barrier. The effective diffusivity of interstitial He atom in Ni-based alloys significantly decreases with the increase of the temperature and Cr/Mo/W concentration. Moreover, when He aggregates at vacancy, the Cr/Mo/W can weaken the formation energy of He clusters and hamper their growth to larger sizes. All these results provide microscopic insights into Cr/Mo/W alloying effect on helium behaviors in Ni-based materials.