【摘要】 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(Eform)、价电子浓度(VEC)、弹性常数(Cij)、剪切模量(G)与体模量(B)的比值(G/B)以及派-纳力(τP-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Nb4c、Nb4c、Si4a和Si8h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.更多还原

【Abstract】 The structural stability and mechanical properties of α-Nb5 Si3 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-Nb5 Si3 alloys retain the stable D81 structure, in which the alloying elements Ti, Cr, Al and B prefer to occupy the Nb4c, Nb4c, Si4aand Si8hsites of α-Nb5 Si3, respectively. The addition of Ti, Al and B increase the brittleness of D81 structured α-Nb5 Si3, while Cr addition is beneficial to the toughness of α-Nb5 Si3. Moreover, the influence of the alloying elements on the ductility/brittleness of α-Nb5 Si3 was investigated based on analysis of the electronic structure, density of states and Mulliken population. The increased brittleness of α-Nb5 Si3 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.更多还原