Point defects and hydrogen-permeation behavior of MAX phase Cr2AlC coating by first-principles studies

Because any fuel assembly material will be exposed to extensive irradiation during reactor operation, understanding the effects of irradiation on the microstructure of coatings and structural materials is critical to improving nuclear reactor safety and performance. In the present work, the point defect and behavior of H in the MAX phase Cr2AlC coating are investigated using first-principles calculations. It is found that the electronic structure of MAX phase Cr2AlC material determines its special properties. The formation of Frenkel pairs leads to the expansion of interlayer spacing along the c-axis, which is the initial cause of the phase transition of the MAX phase structure caused by irradiation damage. Meanwhile, the relationship between the energy of intrinsic defect formation and the chemical potential was analyzed, which showed that sufficient C content was conducive to the structural stability of Cr-Al bonds. Additionally, the obtained a lower energy barrier of the H atom moving parallel to the Al plane, indicating that the H-bubble tends to aggregate near the Al atomic panel. This study provides a fundamental understanding of the point defect properties and the behavior of impurities in the MAX phase and provides theoretical support for the study of anti-radiation performance in nuclear applications.