First-principles calculations on bonding characteristic and electronic property of TiC (111)/TiN (111) interface

Highlights

• For all TiC(111)/TiN(111) interfaces, the TL site stacking shows the largest adhesion energy, which is 5.56 J/m²;

• The C-terminated TiC contacting with Ti-terminated TiN structure with TL site shows ionic and covalent characteristics;

• The electronic transition at the most stable interface is smooth;

• At the most interface structure, the charge increased for N in TiN is more than that for C in TiC.

Abstract

The bonding characteristic and electronic property of TiC (111)/TiN (111) interface were investigated by first-principles calculations in this work. 12 geometry structures of TiC (111) /TiN (111) interfaces with TiC or TiN terminations and three stacking sequences were established. The most stable interface configuration (C-terminated structure of TiC contacting with Ti-terminated structure of TiN with TL site) was selected to investigate the bonding nature and the electronic characteristic by the partial density of state (PDOS), charge density, charge density difference, charge density difference and Mulliken population analysis. The results show that the bonding nature at the interface is extremely similar to that in bulk materials, which shows both ionic and covalent characteristics. The PDOS of interfacial atoms of the most stable interface configuration is also extremely similar to those of their homologous bulks, which demonstrates that the electronic transition at the interface is smooth. The results of charge density and charge density difference indicate that the charge increased for N in TiN side is more than that for C in TiC side, which means the ionic bond in TiN is stronger than that in TiC coinciding with the result of Mulliken population analysis.

Introduction

Transition-metal nitrides and carbides, TiC and TiN [1], [2], are widely used as coating materials for their excellent properties, such as low density, high melting point, high hardness, good thermal conductivity, outstanding corrosion and wear resistance [3], [4], [5], [6]. Especially, compared with TiN or TiC monolayer, the microhardness and wear resistance of TiC/TiN multilayer coatings can be improved obviously [7], [8]. Moreover, the pores and other defects, which always occur in a single-layer film, can be decreased by more interfaces of multilayer coatings [9], [10], [11]. It is a problem that TiN monolayer coating was easily oxidized above 500 °C, however, the TiC/TiN multilayer coatings reveal excellent oxidation resistance because TiN coating can be covered by TiC coating [12]. Compared with TiC coating, multilayer coatings also show the larger adhesion properties on steel substrate [13]. Therefore, it is greatly significant to research TiC/TiN multilayer coatings.

Recently, many studies have been reported to obtain better TiC/TiN multilayer thin coatings or films. Azadi et al. [10] investigated TiN/TiC multilayer coatings prepared by plasma assisted chemical vapor deposition (PACVD) on tool steel, which showed that the microhardness, wear resistance and fracture toughness of the coatings can be improved with the increasing of layers. Meanwhile, Devia et al. [14] discussed the influence of substrate temperature on the structural properties of TiN/TiC films, and found that the crystallinity is increased by increasing the substrate temperature. To further optimize the properties of TiN/TiC coatings, Zhang and Han et al. [15], [16] added some function-providing elements including Nickel and Boron in the coatings. Apart from the experiments research, Yang et al. [17] realized the importance of the relationship between the electronic structure and properties of the coatings.

First-principles investigation on TiN or TiC has been tested as an effective method [18], [19], [20]. Yang et al. [17] studied the mechanical properties of TiN and TiC by first-principles calculation and found that the ultra-hardness of TiN and TiC is caused by hybridization between Ti-3d and non-metal 2p electrons. Wang et al. [21]found that the strong TiC covalent bonding and its relaxation resulted in the changes for the outmost three layers. On the other hand, Ilyasov et al. [22] considered the effect of vacancies on the structural and electronic property of TiC (111) surfaces and obtained that chemical activity of (111) surface is higher than that of (001) surface. Knight et al. [23] employed some methods to study TiC (111) and TiN (111) microstructure, which indicate that the coating hardness of TiC and TiN is affected by temperature. Ruberto et al. [24] studied the chemisorption on TiC (111) and TiN (111) surfaces and found the chemisorption of (111) surface is stronger than that of (001) surface. Although many studies on TiC and TiN coatings have been carried out and some results have been obtained. However, few articles reported about the bonding characteristic and electronic property of the interface of TiC (111)/TiN (111). Therefore, it is meaningful to study the relationship of TiC (111)/TiN (111) interfaces.

In this work, the TiC (111)/TiN (111) interface was selected. Subsequently, the interfacial atomic structure, interfacial ideal work of adhesion and their charge distribution were calculated using density functional theory, which can investigate the interfacial properties of TiC (111)/TiN (111) interfaces effectively.