Theoretical investigation on helium incorporation in Ti3AlC2

Ti3AlC2 known as representing material in MAX phases, has been suggested for next generation nuclear reactor applications for their advantages of thermal/mechanical properties in high temperature and radiation damage resistance. In this paper the helium incorporation properties in Ti3AlC2 are investigated via ab initio methods. The energetically preferred interstitial sites of helium atom in Ti3AlC2 are identified with respect to the chemical potential of each component element. The formation energies of interstitial and substitutional helium atoms are compared to decide the most favorable sites for He in Ti3AlC2 lattice. The calculations show that in most situations helium atom favors the interstitial sites in aluminum layer, whereas it is more likely to substitute on Al sites in the (Ti- and C-rich) environment. Furthermore, the energetics of vacancies were calculated because the presence of single vacancies and bivacancies in the early stage of irradiation damage is thought to modify He behavior in materials to a great extent. These preliminary results lay a solid foundation for further understanding of the underlying mechanisms of helium bubble nucleation and formation in Ti3AlC2.