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

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（ΔH_f）、结合能(ΔE_coh)、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（f_m）和派-纳力(τ_P-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Mulliken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Ti^6g―Si^6g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Si^6g位置时,形成了键强较弱的Al^6g―Si^6g键、Ti^6g―Al^6g键和Ti^4d―Al^6g键,同时降低了D8₈-Ti₅Si₃中Ti^6g―Si^6g键的强度和数量,从而提高了D8₈-Ti₅Si₃的韧性.当D8₈-Ti₅Si₃晶体中Si^6g位置被3个Al原子所占时,Al^6g―Si^6g键消失,而Ti^6g―Si^6g键的强度增加,导致Ti₅(Si_1-xAl_x)₃的脆性增加.

First-Principles Study into the Effect of Substitutional Al Alloying on the Mechanical Properties and Electronic Structure of D88-Ti5Si3

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 ((ΔH_f), cohesive energies (ΔE_coh), bulk modulus (B), shear modulus (G),Poisson's ratio (ν), Cauchy's pressure (C₁₂-C₆₆,C₁₃-C₄₄), metallicity (f_m), and Peierls stress (τ_P-N) were calculated. To develop a better understanding of the effects of substitutional Al alloying on the toughness/brittleness of D8₈-Ti₅Si₃ from an electronic structure point of view the density of states, charge density differences and Mulliken population were determined. The results show that the intrinsic brittleness of D8₈-Ti₅Si₃ comes from strong covalent bonding between Ti^6g and Si^6g.When one or two Ti atoms occupy Si sites in the D8₈- Ti₅Si₃ crystal the intensity of covalent bonding between Ti^6g and Si^6g is reduced and the metallicity increases. This is accompanied by the presence of low intensity Al^6g―Si^6g, Ti^6g―Al^6g, and Ti4d―Al^6g bonds. However, when three Ti atoms occupy Si sites in the D8₈-Ti₅Si₃ crystal the Al^6g―Si^6g bonds disappear and the intensity of covalent bonding between Ti^6g and Si^6g increases leading to an increase in brittleness.