| 其他摘要 | The transition-metal carbides (TMC) and nitrides (TMN) own extraordinary properties, such as high melting temperature, high hardness, and good in anti-corrosion. Therefore, they are widely used in industry area, such as hard coating, anti-corrosion coating, and metal-ceramic composites materials. The knowledge of ceramic surface and interface are crucial for the design, fabrication and application of ceramic materials. In this study, density functional theory (DFT) calculations are carried out to systematically investigate the surface and interface of carbides and nitrides ceramic.
First, the surface structure, rumpling and electronic structure of IVB and VB transition metal carbides are studied. The linear relationship between the bulk cohesive energy and surface energy is found. And they both increase with the increment of atomic number as the periodicity. In addition, the surface rumpling can decreases the surface energy. Therefore, the bulk cohesive energy and surface rumpling affect the surface energy together.
Next, the rumpling, cleave energy and surface stabilities of ternary ceramic Ti3SiC2 and Ti3AlC2 are investigated. The calculated cleave energies explain the mechanical difference between Ti3SiC2 and Ti3AlC2. The surface rumpling of Ti3SiC2 and Ti3AlC2increases with the surface bond strength. From thermodynamic point of view, the stabilities of Ti3SiC2 and Ti3AlC2 surfaces are dependent on the chemical potential of componential atoms. The most stable surface structure is predicted, which is consistent with available experimental results.
Further, TiN/VN (001) interface, as a typical case of nitrides related interface, is investigated. The fully relaxed structure, interface bonding and work of adhesion of interface system are calculated. The results indicate that the preferred stacking sequence of the TiN/VN (001) interface inherits the NaCl structures of TiN and VN bulk. And TiN/VN (001) is a strong adhesive interface with a relatively large work of adhesion, 2.11 J/m2. The electronic structure analysis shows that there are strong chemical bonds of Ti-N and V-N at the interface.
Finally, the effects of alloy elements (Mg and Zn) on the mechanical properties of Al/TiN (001) interface are investigated. Both Mg and Zn decrease the work of adhesion of Al/TiN (001) interface. For the pure Al/TiN (001) interface, the fracture point is in the metal side. For the Zn and Mg introduced system, the fracture point of is at the interface bond and the ideal tensile strength is less than the pure interface system. In addition, the energy barriers of interface sliding show an increasing relationship with the work of adhesion of interface. These studies provide some basic understandings of the ceramic surface and interface on atomic scale. |
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