钨硅二元体系化合物稳定性,力学性能和电子结构的理论计算研究

Due to high melting point, high strength, strong oxidation resistance and deformation resistance at elevated temperature, refractory metal silicides have attracted extensively attention. In the refractory metal silicides, the tungsten-silicon binary compounds, where tungsten has the highest melting point, not only have the similar mechanical and physical properties compared to other metal silicides, but also show many other excellent performance characteristics. The theoretical investigation of tungsten-silicon binary compounds was presented by first-principles calculation to fully exploit the potential performance of tungsten-silicon binary compounds. Two prototype structures of WSi₂ compounds and three prototype structures of W₅Si₃ compounds had been taken into account: α-WSi₂ (C40), β-WSi₂ (C11_b), W₅Si₃-prototype structure (D8_m), Cr₅B₃-prototype structure (D8_l) and Mn₅Si₃-prototype structure (D8₈). The formation enthalpies were calculated to analyze the stabilities, and the elastic constants, bulk modulus, shear modulus, tensile modulus, Poisson's ratio, anisotropy factor and Vickers hardness were calculated to obtain the mechanical properties. Otherwise, the total and partial density of states were also calculated to obtain the bonding mechanisms of tungsten-silicon binary compounds. The stability calculation indicated that the stability sequence of the five tungsten-silicon compounds forms the following order: β-WSi₂>α-WSi₂>W₅Si₃-prototype structure>Mn₅Si₃-prototype structure>Cr₅B₃-prototype structure, and the results of density of state further verified it. The calculation results of mechanical properties showed that the five stable phases of WSi₂ and W₅S₃ with good shape, toughness and hardness are agreement with the mechanical stability. Among them, the shape, toughness and hardness of β-WSi₂ are the highest, while those of Cr₅B₃-prototype structure are the lowest. The calculation of elastic constants showed that for α-WSi₂, Mn₅Si₃-prototype structure, W₅Si₃-prototype structure and Cr₅B₃-prototype structure, the bondings along [100] and [010] directions are stronger than that along [001] direction, and the [100](010) shear is easier than [100](001) shear. On the contrary, for β-WSi₂, the bondings along [100] and [010] directions are weaker than that along [001] direction, and the [100](010) shear is similar with the [100](001) shear. The results of total and partial density of states exhibited that the bonding mechanisms of these five compounds are all the mixture of strong covalent and certain metal bonds. In this paper, a new idea and theoretical foundation of new materials based on tungsten-silicon binary compounds will be provided.