  Cr2AlC materials were irradiated with 7 MeV Xe26+ ions and 500 keV He2+ ions
at room temperature. A structural transition with an increased c lattice
parameter and a decreased a lattice parameter occurs after irradiation to doses
above 1 dpa. Nevertheless, the modified structure is stable up to the dose of
5.2 dpa without obvious lattice disorder. The three samples irradiated to doses
above 1 dpa have comparable lattice parameters and hardness values, suggesting
a saturation of irradiation effects in Cr2AlC. The structural transition and
irradiation effects saturation are ascribed to irradiation-induced antisite
defects (CrAl and AlCr) and C interstitials, which is supported by the
calculations of the formation energies of various defects in Cr2AlC. The
irradiation-induced antisite defects and C interstitials may be critical to
understand the excellent resistance to irradiation-induced amorphization of MAX
phases.
