The studies of electronic structure, mechanical properties and ideal fracture behavior of U3Si1.75Al0.25: first-principle investigations

Abstract

As one of the accident-tolerance nuclear fuels with potential application prospects, U3Si2 shows its merits of high melting point, high thermal conductivity and high uranium density. However, the mechanical brittleness is one major problem for its practical applications. The strategy of Al-alloying could effectively improve the ductility of U3Si2, yet the intrinsic mechanism is not clear. In this work, the mechanisms for the ductility enhancement of U3Si2 via substituting Al into Si site (i.e. U3Si1.75Al0.25) is studied from two aspects: 1) the interatomic bonding characteristics that are responsible for the ductility enhancement are analyzed in detail; 2) the tensile-shear tests of U3Si1.75Al0.25 are carried out via first-principle calculations, and then the ductility-enhancing mechanism is analyzed. It is found that the increasing number of bonding electrons in U–U layer results in the enhancement of the d-σ interactions between U–Si and U–Si–Al six-membered rings, while the decreasing number of bonding electrons within U–Si layer corresponds to the weakening of the d-s interactions. Finally, one electronic structure model is proposed to picture the interactions of bonding electrons during the tensile-shear tests; providing a novel and inspiration logic of mechanical property modification for alloying-U3Si2.