New insight into the helium-induced damage in MAX phase Ti3AlC2 by first-principles studies

Abstract

In the present work, the behavior of He in the MAX phase Ti 3 AlC 2 material is investigated using first-principle methods. It is found that, according to the predicted formation energies, a single He atom favors residing near the Al plane in Ti 3 AlC 2 . The results also show that Al vacancies are better able to trap He atoms than either Ti or C vacancies. The formation energies for the secondary vacancy defects near an Al vacancy or a C vacancy are strongly influenced by He impurity content. According to the present results, the existence of trapped He atoms in primary Al vacancy can promote secondary vacancy formation and the He bubble trapped by Al vacancies has a higher tendency to grow in the Al plane of Ti 3 AlC 2 . The diffusion of He in Ti 3 AlC 2 is also investigated. The energy barriers are approximately 2.980 eV and 0.294 eV along the c-axis and in the ab plane, respectively, which means that He atoms exhibit faster migration parallel to the Al plane. Hence, the formation of platelet-like bubbles nucleated from the Al vacancies is favored both energetically and kinetically. Our calculations also show that the conventional spherical bubbles may be originated from He atoms trapped by C vacancies. Taken together, these results are able to explain the observed formation of bubbles in various shapes in recent experiments. This study is expected to provide new insight into the behaviors of MAX phases under irradiation from electronic structure level in order to improve the design of MAX phase based materials. C 2015 AIP Publishing LLC. [http://dx

Aggregation of retained helium and hydrogen in titanium beryllide Be12Ti: a first-principles study

“…[20][21][22] In particular, the early stage of nucleation of He or H bubbles has been widely simulated by rstprinciples calculations. [23][24][25] For pure Be, the calculated formation energy of a monovacancy is consistent with the data deduced from experiment. 26 Divacancies in Be are energetically unstable, 27 but He atoms could stabilize the divacancies when they bind to divacancy clusters, which are in specic orientations.…”

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

“…Generally, He atoms are rarely dissolved in the MAX phases because of high the formation energies for He‐substrate complexes and easy diffusion desorption for He atom diffusion along the A atomic layer due to its very low the activation energy, for example, 0.05 eV for Ti 3 SiC 2 42,43 . Once the energetic He is introduced into the material, in addition to producing displacement damage, it has a strong tendency to precipitate into bubbles, causing the formation of both finite size defects (He bubbles and self‐interstitial atoms) and extended defects such as dislocation networks.…”

Helium-induced damage in U3Si5 by first-principles studies

“…6 A number of theoretical studies on the behavior of ssion products in U-Si compounds has been reported, including H, H 2 , Xe, Zr, Sr, Ba, Nd, and Ce. [6][7][8][9][10][11][12][13][14][15] Helium, one of the main gases in LWR, has a low diffusion barrier within materials, such as metals and even the MAX phase Ti 3 AlC 2 ; 16 thus, it tends to aggregate and form bubbles within these materials. However, the He gas behavior in U 3 Si 5 , which has one of the very important fuel performance behaviors in U 3 Si 5 , are not yet understood.…”