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O. M. Berdnikova, Yu. M. Tyurin, O. V. Kolisnichenko, О. S. Kushnarova, Ye. V. Polovetskiy, E. P. Titkov, and L. Т. Yerеmyеyevа
Nanoscale Structures of Detonation-Sprayed Metal–Ceramic Coatings of the Ni–Cr–Fe–B–Si System
0097–0109 (2022)

PACS numbers: 61.72.Lk, 61.72.Qq, 62.20.mt, 62.23.Pq, 81.05.Je, 81.15.Rs, 81.65.Lp

Metal–ceramic composite coatings are widely used to improve the reliability and durability of the products, whose operational properties are determined by the properties of their working surfaces. It allows using them in extreme conditions like high temperature and pressure, intensive wear, alternating loads, etc. A promising way to improve the performance properties and durability of products is the application of functional coatings on their surface by multichamber detonation spraying, technology and equipment for which were developed at the Paton Electric Welding Institute of the N.A.S. of Ukraine. A characteristic feature of the structure formed by high-speed modes of detonation spraying of various materials (Al₂O₃–Al/Ti, ZrSiO₄, WC–Co–Cr, Cr₃C₂–NiCr, Cr₃C₂–TaC–NiCr) on various substrates (steel, copper, aluminium, titanium) is the presence of the fragmented substructure and nanoparticles of hardening phases. The formation of the nanostructures increases strength, toughness and fracture toughness of coatings. One of the areas of application of the multichamber detonation technique is spraying of the alloys based on the Ni–Cr system to increase the wear resistance of products operating in high temperatures and chemically active environments. The goal of this work is to establish the patterns of formation of the structural–phase composition of detonation metal–ceramic coatings of the Ni–Cr–Fe–B–Si system and its influence on the strength and crack resistance. Studies of the coatings are performed using a methodological approach that includes light, scanning and transmission electron microscopies and x-ray diffraction phase analysis. The sprayed powder consists of a solid solution based on nickel and chromium containing the boride, silicide and carbide phases in pure form, as well as intermetallides and carboborides in small quantities. Significant differences in phase composition between coatings sprayed on different modes are not detected. The presence of solid solution phases based on Ni–Cr, nickel and chromium borides, as well as small amounts of nickel silicide and chromium carbide is revealed. As established, the increase in heat input and powder size provides the formation of the largest coating thickness with the maximum proportion of lamellae with increasing microhardness and minimum porosity, formation of dispersed substructure with uniform distribution of phase nanoparticles and gradient-free dislocation density. The correlation between the structure and properties of strength, level of local inner stress and localized deformation formed in the coatings is established. A high level of strength and crack resistance of coatings are provided by the fine-grained grain and subgrain structures with uniform distribution of reinforcing phases and dislocation density. It is shown that high speeds of detonation spraying cause the formation of a nanostructured state in coatings, which increases their strength and crack resistance. The formation of the substructure and nanoparticles of the phases with their uniform distribution in the matrix of coatings contributes to the increase of substructural and dispersion hardening. The gradient-free distribution of dislocation densities during the formation of the dispersed structure prevents the formation of concentrators of local internal stress and zones of deformation localization in the coatings.

Key words: metal-ceramic coatings, detonation spraying, microstruc-ture, phase nanoparticles, dislocation density, strength, crack resistance.

https://doi.org/10.15407/nnn.20.01.097