The stability, mechanical properties, electronic structures and thermodynamic properties of (Ti, Nb)C compounds by first
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rst principles was carried out studying the properties of (Ti, Nb)C compounds based on density functional theory. The integration of mechanical behavior, electronic structures, and thermodynamic properties can be optimized by mediating the concentration of the titanium alloying element. The results revealed that these transition metal compounds were stable with the negative formation energy. Nb0.5Ti0.5C (29.15 GPa) demonstrated the largest hardness characterized by moduli (B, G) because of the stable shell configuration. NbC exhibited the strongest anisotropy from the universal anisotropic index (AU) and three-dimensional surface contours. TixNb1xC compounds displayed relatively strong stress responses along the [001], [110], and [111] directions. Due to the weakening p–d bonding, the ideal tensile strength gradually decreased with the increasing titanium concentration. The electronic structures revealed that the bonding characteristics of the (Ti, Nb)C compounds were a mixture of metallic and covalent bonds. On the other hand, NbC and TiC exhibited a minimum (740.55 K) and maximum (919.29 K) Debye temperature, indicating the stronger metalic bonds of NbC and covalent bonds of TiC.
I. INTRODUCTION
Laser cladding, as a new surface strengthening and repairing technology, possesses excellent characteristics, such as fine microstructure, little stress deformation, small heat-affected zone, low dilution ratio, and better metallurgical bonding with the substrate.1–4 It shows good application prospects in the aspect of improving the wear resistance and corrosion resistance of materials. Especially in recent years, many researchers at home and abroad combined metal matrix composites with laser cladding. The cladding coating was obtained with both the ductility and toughness of the metal, as well as the high strength and high modulus of the reinforcing phase by adding a high-performance second phase (usually ceramic phase) into the matrix.5–8 At present, there is more research on composite ceramic phases, such as (V, Cr)C, (Ti, V)C, (Ti, Zr)C, (Ti, W)C, (Ti, Nb)C, etc.9–15 Researchers have done extensive experiments to study the mechanical properties of these composite carbides. However, the information obtained was very limited because of the limitation of experimental conditions and the complexity of the experimental methods. In recent years, the investigation of transition metal composite properties with the method of a first-principles Contributing Editor: Susan B. Sinnott Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2017.440
pseudopotential plane wave based on density functional theory (DFT) has attracted the interest of researchers. Some results have been reported. For example, Jang et al.16 investigated the lattice parameters, formation energy, and bulk moduli of (Ti, Nb)C, (Ti, V)C, (Ti, Mo)C, and (Ti, W)C with first-principles calculations. They showed that the replacement at zero Kelvin of Ti by Mo or W was larger than that of TiC, it was energe
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