Ti,Cr, Al和B合金化元素对α-Nb5Si3力学性能和电子结构的影响

采用基于密度泛函理论(DFT)的第一性原理方法，通过比较形成能(E_form)、价电子浓度(VEC)、弹性常数(C_ij)、剪切模量(G)与体模量(B)的比值(G/B)以及派-纳力(τ_P-N)等参量的变化，研究了Ti、Cr、Al和B合金化对D8₁结构的α-Nb₅Si₃结构稳定性和力学性能的影响. 研究表明：合金化元素Ti、Cr、Al和B分别优先占据α-Nb₅Si₃中Nb^4c、Nb^4c、Si^4a和Si^8h位置；添加不同含量合金化元素的α-Nb₅Si₃仍保持稳定的D8₁结构；Ti、Al和B合金化使α-Nb₅Si₃的脆性增加，而随着Cr含量的增加，α-Nb₅Si₃的韧性逐渐增强. 此外，态密度(DOS)和Mulliken布居等电子结构的计算结果表明：Ti、Al和B合金化导致α-Nb₅Si₃脆性增加的主要原因是提高了共价键的强度；而Cr合金化的增韧作用主要来源于共价键数量的减少和强度的削弱，以及更多的反键态被占据.

Effects of the Alloying Elements Ti,Cr, Al and B on the Mechanical Properties and Electronic Structure of α-Nb5Si3

The structural stability and mechanical properties of α-Nb₅Si₃ alloyed with Ti, Cr, Al and B were investigated using first- principles methods based on density functional theory (DFT) by comparing the formation energy, valence electron concentrations, elastic constants, the shear modulus/bulk modulus ratio, and the Peierls stress. The results show that the structures of the α-Nb₅Si₃ alloys retain the stable D8₁ structure, in which the alloying elements Ti, Cr, Al and B prefer to occupy the Nb^4c, Nb^4c, Si^4a and Si^8h sites of α-Nb₅Si₃, respectively. The addition of Ti, Al and B increase the brittleness of D8₁ structured α-Nb₅Si₃, while Cr addition is beneficial to the toughness of α-Nb₅Si₃. Moreover, the influence of the alloying elements on the ductility/brittleness of α-Nb₅Si₃ was investigated based on analysis of the electronic structure, density of states and Mulliken population. The increased brittleness of α-Nb₅Si₃ by the addition of Ti, Al and B can be attributed to enhanced orientation of the covalent bonds, whereas Cr addition weakens the number and strength of covalent bonds and more anti-bonding states are occupied, thus improving the toughness.