Al代位合金化对D88-Ti5Si3力学性能与电子结构影响的第一性原理研究

摘要

采用基于密度泛函理论(DFT)的第一性原理赝势平面波方法,计算了不同数量的Al原子代位六方D88结构的Ti5Si3晶体中的Si原子后的形成能(ΔHf)、结合能(ΔEcoh)、体模量(B)、剪切模量(G)、泊松比(ν)、Cauchy压力参数(C12―C66,C13―C44)、金属性(fm)和派-纳力(τP-N)等参数,表征了Al合金化对D88-Ti5Si3的结构稳定性和力学性质的影响。结合态密度、差分电荷密度图和Mul iken布居等电子结构分析,揭示了Al原子的添加量对D88-Ti5Si3的韧/脆性变化的影响机制。研究表明, D88-Ti5Si3晶体中强的Ti6g―Si6g方向共价键是导致其室温脆性的主要原因。当1个和2个Al原子占据D88-Ti5Si3晶体中Si6g位置时,形成了键强较弱的Al6g―Si6g键、Ti6g―Al6g键和Ti4d―Al6g键,同时降低了D88-Ti5Si3中Ti6g―Si6g键的强度和数量,从而提高了D88-Ti5Si3的韧性。当D88-Ti5Si3晶体中Si6g位置被3个Al原子所占时, Al6g―Si6g键消失,而Ti6g―Si6g键的强度增加,导致Ti5(Si1-xAlx)3的脆性增加。%The influence of the substitution of Al for Si on the structural stability and mechanical properties of D88-Ti5Si3 was determined using first-principles pseudopotential plane-wave methods based on density functional theory. Several parameters including formation enthalpies ((ΔHf), cohesive energies (ΔEcoh), bulk modulus (B), shear modulus (G), Poisson′s ratio (ν), Cauchy′s pressure (C12-C66,C13-C44), metal icity (fm), and Peierls stress (τP-N) were calculated. To develop a better understanding of the effects of substitutional Al al oying on the toughness/brittleness of D88-Ti5Si3 from an electronic structure point of view the density of states, charge density differences and Mul iken population were determined. The results show that the intrinsic brittleness of D88-Ti5Si3 comes from strong covalent bonding between Ti6g and Si6g. When one or two Ti atoms occupy Si sites in the D88-Ti5Si3 crystal the intensity of covalent bonding between Ti6g and Si6g is reduced and the metal icity increases. This is accompanied by the presence of low intensity Al6g―Si6g, Ti6g―Al6g, and Ti4d―Al6g bonds. However, when three Ti atoms occupy Si sites in the D88-Ti5Si3 crystal the Al6g―Si6g bonds disappear and the intensity of covalent bonding between Ti6g and Si6g increases leading to an increase in brittleness.