The Search for New Super- and Ultrahard Materials: Go Nano!

Super- (H ≥ 40 GPa) and ultrahard (H ≥ 80 GPa) nanostructured and nanocomposite thin films, which have been developed during the last two decades, are finding an increasing number of applications, such as wear-protective coatings on tools, hard and self-lubricant coatings for harsh and variable environment, for corrosion protection and others. Increasing interest receive materials with a high ratio of hardness to Young's modulus as mechanically adaptable coatings on machine parts, where their high compliance combined with high hardness reduce the wear. After a brief overview of the the recent search for new super- and ultrahard materialds I shall concentrate on the progress achieved in the understanding of the properties, preparation and industrial applications of hard and superhard nano-structured coatings on tools for machining (drilling, milling, turning), forming, stamping, injection moulding and the like

Comparative first-principles molecular dynamics study of TiN(001)/SiN/TiN(001) and TiN(001)/SiC/TiN(001) interfaces in superhard nanocomposites

Heterostructures TiN(001)/SiN/TiN(001) and TiN(001)/SiC/TiN(001), with one monolayer (ML) of interfacial SiN and SiC, respectively, inserted between five monolayer thick B1-TiN, were investigated using first-principles quantum molecular dynamics (QMD) calculations. The temperature dependent QMD simulations at 300 K in combination with subsequent variable-cell structural relaxation revealed that the TiN(001)/SiN/TiN(001) interface exists as pseudomorphic B1-SiN layer only at 0 K, and as a superposition of distorted octahedral SiN6 and tetrahedral SiN4 units aligned along the (110) direction at a finite temperature. Thus, at 300 K, the interfacial layer is not epitaxial. Instead it consists of aggregates of the B1-SiN-like and Si3N4-like distorted clusters. However, in the the TiN(001)/SiC/TiN(001) heterostructures, the interfacial layer remains epitaxial B1-SiC at 0 K as well as at 300 K, with only a small shift of nitrogen atoms on both sides of the interface towards the silicon atoms. A comparison with the results obtained by earlier "static" ab initio DFT calculations at 0 K shows the great advantage of the QMD calculations that allow us to reveal structural reconstructions caused by thermal activation. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2054

First-Principles Quantum Molecular Dynamics Study of TixZr1-xN(111)/SiNy Heterosrtructures

Heterostructures with 1 monolayer of Si3N4-like Si2N3 interfacial layer between five monolayers thick B1-TixZr1-xN(111), x 1.0, 0.6, 0.4 and 0.0, slabs were investigated by means of first-principles quantum molecular dynamics and structure optimization procedure using the Quantum ESPRESSO code. Slabs consisting of stoichiometric TiN and ZrN and random, as well as segregated B1-TixZr1-xN(111) solutions were considered. The calculations of the B1-TixZr1-xN solid solutions as well as of the heterostructures showed that the pseudo-binary TiN-ZrN system exhibits a miscibility gap. The segregated heterostructures in which the Zr atoms surround the SiyNz interface were found to be most stable. For the Zr-rich heterostructures, the total energy of the random solid solution was lower compared to that of the segregated one, whereas for the Ti-rich heterostructures the opposite tendency was observed. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3518

Study on the influence of the magnetron power supply on the properties of the silicon nitride films

Silicon nitride (Si3N4) films were deposited by magnetron sputtering of silicon target in (Ar+N2) atmosphere with refractive index 1.95 - 2.05. The results of Fourier transform infrared (FTIR) spectrophotometry showed Si-N bonds in the thin films with concentration 2.41·1023 - 3.48·1023 cm-3. Dependences of deposition rate, optical characteristics and surface morphology on rate of N2 flow and properties of magnetron power supply

The high-pressure phase of boron, {\gamma}-B28: disputes and conclusions of 5 years after discovery

{\gamma}-B28 is a recently established high-pressure phase of boron. Its structure consists of icosahedral B12 clusters and B2 dumbbells in a NaCl-type arrangement (B2){\delta}+(B12){\delta}- and displays a significant charge transfer {\delta}~0.5- 0.6. The discovery of this phase proved essential for the understanding and construction of the phase diagram of boron. {\gamma}-B28 was first experimentally obtained as a pure boron allotrope in early 2004 and its structure was discovered in 2006. This paper reviews recent results and in particular deals with the contentious issues related to the equation of state, hardness, putative isostructural phase transformation at ~40 GPa, and debates on the nature of chemical bonding in this phase. Our analysis confirms that (a) calculations based on density functional theory give an accurate description of its equation of state, (b) the reported isostructural phase transformation in {\gamma}-B28 is an artifact rather than a fact, (c) the best estimate of hardness of this phase is 50 GPa, (d) chemical bonding in this phase has a significant degree of ionicity. Apart from presenting an overview of previous results within a consistent view grounded in experiment, thermodynamics and quantum mechanics, we present new results on Bader charges in {\gamma}-B28 using different levels of quantum-mechanical theory (GGA, exact exchange, and HSE06 hybrid functional), and show that the earlier conclusion about significant degree of partial ionicity in this phase is very robust

Experimental study and critical review of structural, thermodynamic and mechanical properties of superhard refractory boron suboxide, B6O

In the present paper we performed the analysis of available data on structural, thermodynamic and mechanical properties of B6O. Although the compound is known for half a century and has been extensively studied, many properties of this boron-rich solid remain unknown or doubtful. Semi-empirical analysis of our experimental and literature data allowed us to choose the best values of main thermodynamic and mechanical characteristics among previously reported data, to predict the thermoelastic equation of state of B6O, and dependence of its hardness on non-stoichiometry and temperature