中文摘要：

利用基于密度泛函理论的第一性原理方法研究了金属元素X（X分别表示V,Nb,Ta,Cr,Mo和W）掺杂对TiAl合金性能的影响.研究发现,掺杂可以有效减小合金的各向异性,增强Ti-Al原子间的相互作用,同时增强金属键性,减弱共价键性,有利于塑性变形.在相同的压力下,不同的掺杂浓度和掺杂元素对体积的影响不同.通过计算不同掺杂体系的弹性常数、体弹模量和剪切模量可知：当掺杂浓度为6.25%时,相对于V,Nb和Ta,Cr,Mo和W掺杂能较好地改善TiAl金属间化合物的韧性;当掺杂浓度为12.5%时,相对其他掺杂元素Mo的韧化作用最强.从Mo掺杂后Ti Al体系的分波态密度和电荷密度图,发现Mo和Ti原子发生强烈的s-s,p-p,d-d电子相互作用,有效地束缚了合金中Ti和Al原子的迁移,有助于提高合金的稳定性和强度.

英文摘要：

TiAl alloy has attracted significant attention as a candidate material with high melting temperature, low density,relatively high hardness and excellent corrosion resistance, good oxidation and creep resistance at high temperatures.The inherent brittleness at low temperatures is by far the greatest hurdle that prevents it from being widely used in industries. Doping has long been considered as an effective way to improve the performance of alloy. The properties of Ti Al alloy are highly dependent on the third alloying element. Although the mechanical properties of Ti Al alloy are improved to a certain extent by adjusting the composition, to date the physical mechanism has been still unclear. In this paper, from the microscopic electronic structure the influence of metal element X（X represents V, Nb, Ta, Cr, Mo and W） doping on the mechanical properties of Ti Al alloy is studied by first-principle method.The first-principle calculations presented here are based on electronic density-functional theory framework. The ultrasoft pseudopotentials and a plane-wave basis set with a cut-off energy of 350.00 eV are used. The generalized gradient approximation refined by Perdew and Zunger is employed for determining the exchange-correlation energy.Brillouin zone is set to be within 8 × 8 × 8 k point mesh generated by the Monkhorst-Pack scheme. The self-consistent convergence of total energy is at 5.0 × 10~（-7）eV/atom. The supercell（2 × 2 × 2）,（2 × 2 × 1） and（1 × 2 × 1） are selected as a computational model.According to the calculated structural parameters of the doped systems, we find that the lattice constant ratio c/a decreases with the increase of doping ratio, correspondingly the anisotropy of crystal reduces. The interactions between Ti and Al atoms are enhanced. Under the same pressure, the influences of doping concentration and type of doping element on volume are different. According to the obtained elastic constants, bulk moduli and shear moduli of doping systems, we find that with a do