2, Peking University, Beijing, Beijing, China
3, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, , China
4, Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo, , China
Radiation-induced phase transitions in hcp Mn+1AXn phases (Ti2AlN, Ti2AlC, and Ti4AlN3) by 1 MeV Au+ ion irradiation were investigated, over a wide range of ion fluences from 1×1014 to 2×1016 cm-2., by transmission electron microscopy (TEM) and synchrotron grazing incidence X-ray diffraction (GIXRD). The transformations of the initial hcp phases to the intermediate γ-phases and fcc phases were observed using high-resolution TEM (HRTEM) images and selected area electron diffraction (SAED). Based on phase contrast imaging and electron diffraction pattern (EDP) simulations, the atomic-scale mechanisms for the phase transitions were determined. By comparing the transformation behavior of Ti2AlN with that of Ti2AlC and Ti4AlN3 under the same irradiation conditions, using both the experimental data and first-principles calculations, the role of the X and n parameters in the radiation responses of different Mn+1AXn phases are elucidated. The susceptibility of materials in this system to irradiation-induced phase transitions were determined with respect to the bonding characteristics and compositions of these MAX phases.