Theoretical Calculation Of High Pressure Physical Properties And Toughening Modification Of Nb₅Si₃

With the rapid development of aerospace technology,high temperature structural materials with high temperature resistance,corrosion resistance,oxidation resistance and creep resistance have attracted more and more scholars'attention.Compared with Fe-based,Ni-based,Co-based superalloys,Nb-Si alloys with high melting point,low density and high temperature strength are considered as one of the most potential ultra-high temperature materials.However,the low plasticity and poor oxidation resistance of Nb-Si superalloy limit its wide application in industry.Therefore,its microstructure mechanical properties,fracture toughness and oxidation resistance mechanism,and their internal relations still need to be further studied.In this paper,the response of Nb-Si superalloy to pressure was studied.Secondly,the effect of vacancy concentration on the electronic structure and mechanical properties of?-Nb₅Si₃ alloy was investigated.Finally,the toughening effect of alloying elements Ti?Hf?Ta?Zr?V?Mo?W?Cr?C?S?O?Se?P?N on?-Nb₅Si₃ was studied.The results show that when the pressure increases to 25 GPa,?-Nb₅Si₃ undergoes a transition from brittleness to toughness,and then the toughness increases with the increase of pressure,that is,the pressure effectively improves the toughness of?-Nb₅Si₃.The calculation results of density of states show that the covalence of Nb₅Si₃ is enhanced by the pressure.Different Nb vacancy concentrations were found that the B/G ratio increases with the increase of Nb vacancy concentration,indicating that the increase of vacancy concentration was beneficial to the transition of?-Nb₅Si₃ from brittleness to toughness.When vacancy concentration is 5%,?-Nb₅Si₃ shows toughness.With the increase of vacancy concentration,the position of density of states of peak moves to the lower energy direction,and the Nb vacancy enhances the hybridization of orbitals between neighboring Nb atoms.The above results indicate that the presence of vacancy can effectively enhance the toughness of?-Nb₅Si₃.The mechanical properties of alloyed?-Nb₅Si₃ have been calculated.The results show that the alloyed?-Nb₅Si₃ has mechanical stability,and the alloyed?-Nb₅Si₃shows brittle behavior.It can be seen from the density of states that there is a pseudogap near the Fermi level,and there are both covalent bonds and metal bonds near the Fermi level.The metal element Ti causes the Fermi level of?-Nb₅Si₃ to gradually move towards the lower energy region of the pseudogap.The structure stability of?-Nb₅Si₃ is enhanced by Ti,while the pseudogap width decreases after alloying Zr?Hf?V?Ta?Cr?Mo?W,the Fermi level moves toward the region of the pseudogap,the Fermi level increases gradually and the stability of the system becomes worse.In conclusion,the above alloying elements do not significantly improve the toughness of?-Nb₅Si₃.