This article presents the results of experimental work on the vacuum–arc deposition of high–entropy monolayer nitride coatings of the (TiZrVCrAl)N system on the surface of substrates made of Ti–6Al–4V structural titanium alloy with an initial coarse–grained and ultrafine–grained structure formed by equal–channel angular pressing. A structural and phase analysis of the formed coatings was performed, and their physical and mechanical properties were assessed. It was found that the formation of an ultrafine–grained structure by methods of severe plastic deformation in the substrate leads to a significant improvement in the characteristics of the monolayer coating compared to the coarse–grained structure: the microhardness of the resulting coating increases from 702.1 to 1283.4 HV, the critical loads of the appearance of the first cracks (Lc1) and local delamination of the coating (Lc2) during the scratch test increase by 33
The paper presents the results of a fractal analysis of model composites with different volume fractions, sizes and shapes of dispersed-phase particles as part of the physicochemical engineering of materials. Models of composites with a random distribution of spherical and rod-shaped particles of various sizes and aspect ratios in the matrix, as well as models with particles segregated along grain boundaries, are proposed and substantiated. Computational experiments were performed to determine the fractal dimension of model composites, and a specific variation in fractal dimension depending on the geometry of the dispersed phase was demonstrated. Characteristic regions in the relationship between fractal dimension and dispersed-phase particle size were identified; these regions are consistent with the conventional classification of particles into ultramicro-, micro-, submicro-, and nanoscale size ranges. The calculated fractal-dimension values for the model composites are consistent with literature data for experimentally obtained composite samples. Optimal dispersed-phase particle sizes required to achieve target fractal-dimension values associated with the performance characteristics of composite materials are proposed. To decrease the fractal dimension of a composite, particles in the micro-size range (0.6–1.5 μm) are preferable, whereas to increase the fractal dimension, particles in the nanoscale range (<0.1 μm) should be used. It is shown that particle segregation along grain boundaries leads to a decrease in fractal dimension. Changes in the aspect ratio of rod-shaped particles were found to cause fluctuations in fractal dimension and, consequently, in composite properties. The numerically obtained results on the effect of dispersed-phase particle size, shape, and concentration on the fractal dimension of composites can be used to describe real composite systems. The results of the computational experiment for different dispersed-phase geometries provide a basis for controlling fractal dimension and properties in the physicochemical engineering and synthesis of new composite materials with desired performance characteristics.
High-entropy alloy (HEA) coatings based on the Cr–Ti–Zr–Nb–Hf system represent a promising class of functional materials intended for application under extreme operation conditions. This study presents a comprehensive investigation of Cr–Ti–Zr–Nb–Hf HEA coatings, both in their as–deposited state and following nitrogen modification. Ion–plasma sputtering of the coatings was conducted in Ar and Ar + N2 atmospheres, respectively. Synchrotron X–ray absorption spectroscopy (XAS) revealed that nitrogen incorporation facilitates the formation of a single–phase high–entropy nitride, designated (Cr, Ti, Zr, Nb, Hf)N, characterized by strong covalent metal–nitrogen bonds and substantial lattice distortion. Nitrogen modification was found to yield more than a twofold increase in hardness and an approximately twofold increase in Young’s modulus in contrast to nitrogen–free sputtering. Tribological tests conducted over a temperature range of –60°C to +150°C demonstrated high thermal stability of the nitride coating. Nitrogen–assisted modification further enhanced wear resistance by nearly an order of magnitude, while the coefficient of friction decreased by a factor of three to four. A model–based description of the structural and mechanical characteristics employing the Miedema model and the Mazhnik–Oganov framework along with an analysis of tribological properties grounded in the Bowden–Tabor and Archard theories, exhibited good agreement with experimental observations. The findings of the study indicate that the (Cr, Ti, Zr, Nb, Hf)N coating represents a stable, high–strength high–entropy compound dominated by covalent interatomic interactions.
The influence of mechanical stresses on the growth process of the perovskite–phase in thin ferroelectric films of lead zirconate–titanate on a silicon substrate, manufactured using a two–stage method of high–frequency magnetron deposition, is investigated. Using X–ray diffraction analysis and scanning electron microscopy, the emergence of a spherulitic grain structure with a linear change in the orientation of the growth anisotropy axes along the spherulite radius was established. The results of an analytical and numerical solution of the boundary value problem for determining the stress state during the growth of periodic perovskite cylindrical inclusions in a pyrochlore matrix are presented. It is shown that a monotonic increase in the configuration force at the interphase boundary with distance from the substrate determines a permanent rotation of growth anisotropy during the film formation. Analytical estimates of the stress state of a two–layer plate (film / substrate) under bending caused by transformational strains during the pyrochlore → perovskite phase transition in the film are also presented. A comparison of the calculation results with the measured data of the deviation angle gradient of the growth anisotropy axes demonstrates satisfactory accuracy.
