Behaviors of helium in Cr₂AlC from first principles

Abstract

The properties of helium incorporation and transport in Cr2AlC have been investigated using first principles method. The results of calculation show that a single helium atom is preferred to reside at an interstitial position near the Al plane in perfect Cr2AlC crystal, attributing to the low predicted formation energy. Helium atoms are expected to aggregate in Al layers. The interaction between helium and lattice atoms is primarily elastic due to the closed‐shell electronic structure of helium. The Doping of helium leads to a weakening of the Cr–Al bonds. Furthermore, an interstitial helium atom is likely to migrate along an indirect migration pathway from the hexahedral interstitial position on Al plane (IAlC), passing by the nearest tetrahedral interstitial position near Al plane (IAlCr), and finally reach to another hexahedral interstitial position (IAlC) with an activation energy of 1.21 eV. The high activation energy suggests a relatively low migration for helium atoms in Cr2AlC as well as a slow growth rate of helium bubbles for the early stage of helium irradiation.

Annealing effects on the structure and hardness of helium‐irradiated Cr2AlC thin films

“…Comparing with the as implanted sample, the He depth profile annealed at 430℃ exhibits a slight decrease in concentration and shift toward the area of damage peak due to the diffusion of He, including dissociated single He atoms from the various He complexes with lower binding energy, along paths with lower migration energies 45 . According to the calculation, 46 the diffusion coefficient of He atom in Cr 2 AlC along the Al plane at 430℃ is 1.67 × 10 −12 cm 2 ·s −1 for an activation energy of 1.3 eV. For an annealing temperature up at 600℃, it seems that the He distribution does not change visibly relative to 430℃ and the further release of He does not occur over this temperature interval.…”

Sintering behavior of Cr2AlC MAX phase synthesized by Spark plasma sintering

“…Due to the high potential of this MAX phase in high temperature applications, this MAX phase has been significantly investigated in power generation and nuclear reactors 9–10 . Among the 60 MAX phases discovered, aluminum‐based MAX phases, such as Cr 2 AlC, Ti 2 AlC, and Ti 3 AlC 2 , are most commonly used in the temperature range of 1000–1300°C 11 .…”