title: First-principles quantum molecular dynamics study of TixZr1-xN(111)/SiNyheterostructures and comparison with experimental results.
abstract: The heterostructures of five monolayers B1-TixZr1-xN(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 Si2N3interfacial 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-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 Zr atoms surround the SiyNzinterface 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 3.5μm 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 TixZr1-xN(111)/SiNysystems. 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.%.
authors.affiliation: Institute of Problems of Material Science, NAS of Ukraine, Krzhyzhanovsky Street 3, 03142, Kyiv, Ukraine.
authors.forename: Volodymyr
authors.initials: V
authors.lastname: Ivashchenko
authors.affiliation: Department of Chemistry, Technical University Munich, Lichtenbergstrasse 4, D-85747, Garching, Germany.
authors.forename: Stan
authors.initials: S
authors.lastname: Veprek
authors.affiliation: Sumy State University, Rymsky-Korsakov Street 2, 40007, Sumy, Ukraine.
authors.forename: Alexander
authors.initials: A
authors.lastname: Pogrebnjak
authors.affiliation: Sumy State University, Rymsky-Korsakov Street 2, 40007, Sumy, Ukraine.
authors.forename: Bogdan
authors.initials: B
authors.lastname: Postolnyi
keywords: Compressive stress; First-principles investigation; Interface; Nanocomposite; Nanograins; Quantum molecular dynamics; Superhard; Ti–Zr–N/SiNx nanolayered coatings