Abinitio Study Of Effects Of Al On The Defect Behavior Of Al_xCoCrFeNi

As the world’s demand for energy is increasing,it is necessary to find a sustainable and clean energy source.As a sustainable clean energy with the great potential,nuclear energy is one of the most promising clean energy for mankind in the future.The nuclear reactors will be safer and more economical in the future.However,the structural materials in the advanced nuclear system are exposed to harsh environments,including high irradiation doses,high temperatures,high stresses,etc.,thus,the development of advanced nuclear system requires novel structural materials with great performances.A large number of studies have shown that high-entropy alloys composed of multiple components have better mechanical properties than traditional alloys and their irradiation resistances are also higher than traditional alloys.However,the irradiation resistance mechanisms of high-entropy alloys are still unclear,which restrains the exploration and development of novel high entropy alloys with high performances using in nuclear systems.As an important microstructural characteristic of high-entropy alloys,the high lattice distortion is believed to be related with the great mechanical properties and irradiation tolerance of HEAs.However,the direct evidence correlating lattice distortion and great irradiation tolerance of HEAs has not been achieved to date.Therefore,Al_xCoCrFeNi(0<x<0.3)was employed in this study,the lattice distortion of system can be significantly modified by varying the Al content.The lattice distortion of Al_xCoCrFeNi and defect properties,including formation energies and migration energies of vacancies and interstitials,were calculated by first-principles method to reveal the effects of lattice distortion on the irradiation responses of HEAs.The calculation results in this study show that the lattice distortion of Al_xCoCrFeNi high-entropy alloy increases with the increasing Al content due to the large atomic radius,and the increase of lattice distortion is not limited near Al atoms.Due to the tensile strain induced by the addition of Al atoms,the average formation energies of interstitials and vacancies are decreased with increase of Al content and the corresponding distributions are also significantly broadening.Furthermore,the migration energies of vacancies are decreased while that of interstitials are increased with increasing Al content,the corresponding migration energy distributions of vacancies and interstitials are also broadening.Based on the calculation results,it is deduced that more defects would be formed in the displacement cascades due to the lower formation energies of interstitials and vacancies.However,more defects would be recombined in the annealing process of displacement cascades and subsequent long-range migration.Therefore,the addition of Al introduces two opposite effects for the irradiation responses of Al_xCoCrFeNi,resulting in that the irradiation resistance of Al_xCoCrFeNi is not monotonously varied with Al content.Further investigations of long time simulations are required to determine optimal Al contents for the irradiation resistances.