Investigations on the microstructure and hardening mechanism of TiN/Si₃N₄nanocomposite coatings

Abstract

A detailed TEM investigation on the microstructure of TiN/Si3N4 nanocomposite coatings, which is believed to be responsible for the coatings' remarkable mechanical properties, was carried out. Parallel simulation utilizing two-dimensional TiN/Si3N4 nanomultilayered coatings was further performed to study whether the variation of Si3N4 interlayer thickness has an influence on the coatings' microstructure and mechanical properties. The results revealed that, in nanocomposite coatings with high hardness, Si3N4 tissue has a thickness of about 0.5–0.7 nm and exists in the crystalline state. Low-energy coherent interfaces are formed between Si3N4 and neighbouring elongated TiN grains. For TiN/Si3N4 nanomultilayered coatings, Si3N4 modulation layers with thicknesses less than 0.7 nm were also found to crystallize and form coherent interfaces with the neighbouring TiN layers; at the same time, the hardness of the coatings is remarkably enhanced. When its thickness exceeds 1.0 nm, Si3N4 transformed its growth mode into amorphous and the coherent interfaces were damaged; as a consequence, hardness enhancements in the coatings vanished. The similarity of the microstructure and the mechanical properties response between nanocomposites and nanomultilayered coatings indicates that the crystallization of Si3N4 as well as the formation of coherent interfaces between TiN and Si3N4 is the main reason for the hardening of the nanocomposites.

Electronic structure, stability, and mechanism of the decohesion and shear of interfaces in superhard nanocomposites and heterostructures

“…1 and 3 of Ref. 17. This is a significant difference when compared to the perfectly isotropic morphology with random orientation of 3-4 nm size nanocrystals in nanocomposites deposited by plasma chemical vapor deposition at 550°C ͑Refs.…”

“…12 The fcc͑NaCl͒-SiN 1-3 ML thin interface, pseudomorphically stabilized between several nm thick TiN layers, has been recently reported in TiN/SiN/TiN heterostructures deposited by reactive sputtering, [13][14][15][16] and it has been suggested to be the prototype of the interface in the "Ti-Si-N nanocomposites." 17 However, a variety of different ͑hkl͒ interfaces, possibly also faceted, have to coexist in superhard nanocomposites deposited at sufficiently high pressure of nitrogen and temperature. These must have randomly oriented TiN nanocrystals, fully segregated, stable Si 3 N 4 -like interfaces and show perfect stability up to Ն1100°C without any internal friction signal.…”

“…3,18 Because the coatings reported in Ref. 17 were deposited at much lower temperature ͑see Refs. 17 and 19͒ than those reported in our papers, [1][2][3]20 they had a pronounced columnar structure and strong preferential orientation of the relatively large ͑Ն10 nm͒ TiN crystals, as seen in Figs.…”

The Electronic and Elastic Properties of Si Atom Doping in TiN: A First-Principles Calculation

“…In 2005, 2006 and 2007 Söderberg et al reported a transmission electron microscopy examination that showed a transition from epitaxially-stabilized growth of crystalline SiN x to amorphous growth as the layer thickness increased from 0.3 nm to 0.8 nm [7][8][9]. In 2007, and in accordance with the HRTEM and ab initio studies, Kong et al and Hultman et al respectively denoted that the interface in superhard TiN-SiN nanocomposites is crystalline [10,11]. In 2009 and 2010, Zhang et al found that a small distortion of the Si-N bond could stabilize the SiN interface sandwiched between fcc (001)-TiN crystallites with their ab initio DFT studies [12,13].…”

Structure characterization and tribological study of magnetron sputtered nanocomposite nc-TiAlV(N,C)/a-C coatings

“…Up to now, polycrystalline multilayer nitride coatings have been successfully developed to show excellent mechanical properties, wear resistance and good performance in various industrial applications [6][7][8]. Another model of superhard structure, comprising TMN nano-crystallites and a grain boundary phase of resin-like SiNx, was first proposed by Veprek and co-workers in the Ti-Si-N system [9][10] and then extended to other systems, such as CrSiN [11] and TiBN [12]. Subsequently comprehensive studies have been carried out on the nanocomposite structure, interface and the hardening mechanisms e.g.…”