The microstructures of two MAX phases, Ti₂AlN and Ti₄AlN₃, irradiated at room temperature with 70 keV He ions over a wide fluence range have been studied to reveal the dependence of MAX phase irradiation tolerance on structure. Grazing incident x-ray diffraction (GIXRD) reveals that a new set of diffraction peaks appears after ion irradiation for both MAX phases and the positions of diffraction peaks gradually shift towards lower 2θ values with increasing fluence. Transmission electron microscope characterizations show both MAX phases experience a similar structure transformation at low fluences, forming an intermediate structure. The d-spacings derived from electron diffraction analysis of intermediate structures are basically consistent with that of new peaks in GIXRD. At high fluences a nano-twinned microstructure is found in Ti₂AlN, but no such microstructure is observed in Ti₄AlN₃. Based on the simulation results of electron diffractions and the irradiation responses of other MAX phases, the structure characteristics and formation mechanisms of the intermediate structure are derived and the discrepancy in the phase stability of both MAX phases at high fluences is discussed.

研究了在宽通量范围内在室温下用70 keV He离子辐照的两个MAX相Ti ₂ AlN和Ti ₄ AlN ₃的微观结构，以揭示MAX相辐照耐受性对结构的依赖性。掠入射X射线衍射（GIXRD）揭示了一组新的衍射峰的两个MAX相和衍射峰的位置离子照射后会出现逐渐朝向较低2个移θ值随通量。透射电子显微镜的表征表明，两个MAX相在低注量下都经历了相似的结构转变，形成了中间结构。该d从中间结构的电子衍射分析得出的-间距与GIXRD中新峰的间距基本一致。在高通量下，在Ti ₂ AlN中发现了纳米孪晶的微观结构，但在Ti ₄ AlN _3中未观察到这样的微观结构。根据电子衍射的模拟结果和其他MAX相的辐照响应，推导了中间结构的结构特征和形成机理，并讨论了高通量下两个MAX相的相稳定性差异。