First-principles quantum molecular dynamics study of Ti x Zr1- x N(111)/SiN y heterostructures and comparison with experimental results

Volodymyr Ivashchenko; Stan Veprek; Alexander Pogrebnjak; Bogdan Postolnyi

doi:10.1088/1468-6996/15/2/025007

First-principles quantum molecular dynamics study of Ti _x Zr_{1- x} N(111)/SiN _y heterostructures and comparison with experimental results

Sci Technol Adv Mater. 2014 Apr 30;15(2):025007. doi: 10.1088/1468-6996/15/2/025007. eCollection 2014 Apr.

Authors

Volodymyr Ivashchenko¹, Stan Veprek², Alexander Pogrebnjak³, Bogdan Postolnyi³

Affiliations

¹ Institute of Problems of Material Science, NAS of Ukraine, Krzhyzhanovsky Street 3, 03142, Kyiv, Ukraine.
² Department of Chemistry, Technical University Munich, Lichtenbergstrasse 4, D-85747, Garching, Germany.
³ Sumy State University, Rymsky-Korsakov Street 2, 40007, Sumy, Ukraine.

Abstract

The heterostructures of five monolayers B1-Ti _x Zr_1-x N(111), x = 1.0, 0.6, 0.4 and 0.0 (where B1 is a NaCl-type structure) with one monolayer of a Si₃N₄-like Si₂N₃ interfacial layer were investigated by means of first-principles quantum molecular dynamics and a structure optimization procedure using the Quantum ESPRESSO code. Slabs consisting of stoichiometric TiN and ZrN and random, as well as segregated, B1-Ti _x Zr_1-x N(111) solutions were considered. The calculations of the B1-Ti _x Zr_1-x N 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 Zr atoms surround the Si _y N _z interface were found to be the 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. Hard and super hard Zr-Ti-Si-N coatings with thicknesses from 2.8 to 3.5 μm were obtained using a vacuum arc source with high frequency stimulation. The samples were annealed in a vacuum and in air at 1200 °C. Experimental investigations of Zr-Ti-N, Zr-Ti-Si-N and Ti-Si-N coatings with different Zr, Ti and Si concentrations were carried out for comparison with results obtained from Ti _x Zr _1-x N(111)/SiN _y systems. During annealing, the hardness of the best series samples was increased from (39.6 ± 1.4) to 53.6 GPa, which seemed to indicate that a spinodal segregation along grain interfaces was finished. A maximum hardness of 40.8 GPa before and 55 GPa after annealing in air at 500 °C was observed for coatings with a concentration of elements of Si≽ (7-8) at.%, Ti ≽ 22 at.% and Zr ⩽ 70 at.%.

Keywords: Compressive stress; First-principles investigation; Interface; Nanocomposite; Nanograins; Quantum molecular dynamics; Superhard; Ti–Zr–N/SiNx nanolayered coatings.