Elsevier

Computational Materials Science

Volume 127, 1 February 2017, Pages 244-250
Computational Materials Science

Adhesion strength and stability of TiB2/TiC interface in composite coatings by first principles calculation

https://doi.org/10.1016/j.commatsci.2016.11.009Get rights and content

Highlights

  • Properties of TiC (1 1 1)/TiB2 (0 0 0 1) interfaces were investigated by first-principles.

  • The Wad of HS interfaces is larger than that of the CS and TS interfaces.

  • The C-HS-T interface exhibits the largest adhesive strength and stability.

  • The C-HS-T interface consists of polar covalent bonding and metallic bonding.

Abstract

Properties of the TiC (1 1 1) surface, TiB2 (0 0 0 1) surface, and TiC (1 1 1)/TiB2 (0 0 0 1) interfaces were investigated by first-principles calculations. Additionally, the work of adhesion (Wad), interface energy (γint), and electronic structure of the TiC/TiB2 interfaces were studied. The calculated results show that the Wad of the hollow-stacked interfaces is larger than those of the center- and top-stacked interfaces. Among the interfaces of C/Ti-terminated hollow-stacked (C-HS-T), Ti/Ti-terminated hollow-stacked (Ti-HS-Ti), and Ti/B-terminated hollow-stacked (Ti-HS-B), the C-HS-T interface exhibits the largest Wad (11.43 J/m2), the smallest interfacial separation d0 (1.208 Å) and thus is the most stable. For the entire range of Ti chemical potential, the interfacial energy of the Ti-HS-Ti supercell was 1.04–4.59 J/m2, while the interfacial energy was 0.54–0.58 J/m2 and 0.45–0.49 J/m2 for Ti-HS-B interface and the C-HS-T interface respectively. Furthermore, the C-HS-T interface consists of strong polar covalent bonding and weak metallic bonding, while the Ti-HS-B and the Ti-HS-Ti interface consists of primarily covalent and metallic bonding, respectively.

Introduction

Owing to the high melting point and hardness, the excellent wear-resistance and stability, the ceramics of titanium compounds, such as cermet coatings, metal matrix composites, and cemented carbide, have been widely investigated for the further industrial applications [1], [2], [3]. Due to the excellent strength, hardness, and ductility of the matrix/TiB2 coherent interfaces, titanium diboride (TiB2) has received considerable attention [3], [4], [5], [6], [7], [8], [9]. For example, Zhu [3] studied the microstructure and mechanical properties of plasma sprayed TiB2–Ni cermet coatings, and concluded the coatings obtained by agglomerated powder exhibited a better abrasive wear resistance than that obtained by clad powder. Similar works have also been conducted for the coatings of Ni60–TiB2 [5] and Ni(Cr)–TiB2 [6], which are obtained by high velocity oxy-fuel spraying. With the dual-cathode magnetron sputtering, a Ti–TiB2 nanocomposite coating was produced [8], and the “flatter” hardness-toughness relationship of the coatings was observed. Wu [10] found that a defect-free TiB2/Fe coating could be produced by the plasma transferred-arc technique with an optimal energy density and heat input.

To improve the properties of TiB2-containing multilayered coatings, such as TiB2/c-BN [11], TiB2/Fe1−xMnx [12], TiB2/TiN [13], and TiB2/TiC, several studies have been conducted [14], [15], [16], [17], [18]. Work by Tang [14] indicated that the hardness of the TiC-TiB2 coating prepared by electro spark deposition was four times, and the wear resistance was five times, higher than that of the substrate. Huang [17] found that TiB2-TiC composites exhibited greater hardness, flexural strength, and fracture toughness than those of single TiC and TiB2 ceramics. Yang [16] proposed that the optimal content of TiB2 was 10 vol.% such that TiB2-TiC composite with finer micro-tissue and good mechanical properties could be made. Moreover, Luo [15] found that the mechanical properties of TiB2–TiC coatings deposited on electrodes under argon atmosphere were far superior to those manufactured in air. All of the studies indicated that the characteristics of the interface has significant impact on the properties of these coatings. However, it is difficult to clearly understand the interaction of the TiB2/TiC interface at the atomic or even electronic scale through experimental methods.

First-principles calculations, which are capable of revealing the atomic and electronic structures of interfaces as well as the interfacial stability and adhesion strength, are used extensively to study solid–solid interfaces [19], [20]. Jin [21] used a first-principles method to investigate the atomic structure, stability, and electronic properties of the W/WC interface. The study revealed that the C-terminated interfaces have a larger adhesion energy than the other interfaces, and thus are the most stable structure. Yin [22] used a first-principles method to investigate the tensile and fracture process of the TiN/VN interface and found that fracture typically occurs between the second and third layers of the VN side. Studies using first-principles calculations concluded that Ti and Fe can improve the stability of the Al/TiC interface while Zn and Mg present negative effects [23]. And the misfit dislocation could decrease the adhesion strength of the Al/TiC interface [24]. In addition, Ce could reduce the interfacial energy of Al/TiB2 interfaces and improve dispersion of TiB2 particles in composite melt [25].

The TiC/TiB2 interface relationship has a significant effect on the adhesion strength of the TiC-TiB2 composite coating, and hence the purpose of this works is to investigate TiB2/TiC interfaces with the help of first-principles calculations. Additionally, the work of adhesion, interfacial energy, electronic structure, and bonding characteristics of the TiC (1 1 1)/TiB2 (0 0 0 1) interface were investigated.

Section snippets

Calculation method and details

The calculations in this work were all performed with the Cambridge Serial Total Energy Package Code (CASTEP) [26], [27], which is based on the density functional theory (DFT). The interaction between the ionic core and the valence electrons was described by the plane-wave ultra-soft pseudopotential method [28]. Furthermore, the 3s23p63d24s2 for Ti, 2s22p2 for C, and C2s22p1 for B were chosen as the valence electrons of the atoms. The local density approximation (LDA) of the

Bulk properties of TiB2 and TiC

To guarantee the rationality and accuracy of the calculation, the lattice constant, volume, bulk modulus and formation enthalpy for TiB2 and TiC were calculated by two different functions (LDA-CAPZ, GGA-PBE). The formation enthalpy of bulk TiB2 and TiC is obtained from [31], [32]:ΔrH(MxNy)=Etot(MxNy)-xEbulk(M)-yEbulk(N)/(x+y)where ΔrH(MxNy) and Etot(MxNy) are the formation enthalpy and the total energy of TiB2 or TiC, respectively, Ebulk(M) is the cohesive energy of pure α-Ti, Ebulk(N) is the

Conclusions

To reveal the bond strength and stability of different TiC/TiB2 interfaces, the work of adhesion, interfacial energy, electronic structure and bonding characteristics of TiC/TiB2 interfaces have been studied by first principles calculation. Nine (Ti-HS-Ti, Ti-HS-B, and C-HS-Ti) interfaces were investigated in this work. The results are as follows:

  • (1)

    The nine-layered TiB2 (0 0 0 1) and TiC (1 1 1) surfaces exhibited bulk-like interior characteristics. For a small value of ΔμTi, the B-terminated TiB2 (0 0 0

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