Loskutova T.V. Formation of multicomponent coatings with the participation of Ti, Cr, Al with barrier layers on steels, titanium and solid alloys - Qualifying scientific work on the rights of the manuscript.
The dissertation on obtaining of a scientific degree of the doctor of technical sciences on a specialty 05.16.01 - Metallurgy and thermal treatment of metals (05 - Technical sciences). National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute", Kyiv, 2020.
The dissertation is devoted to the solution of an important scientific and technical problem: development of scientific bases of creation of multicomponent coatings with barrier layers which structure includes chromium carbides, titanium carbide, titanium nitride, intermetallics of aluminium, chromium and titanium. The resulting coatings combine the required performance properties of some components (wear resistance, heat and corrosion resistance) with the barrier functions of others.
Theoretical calculations of the equilibrium composition of multicomponent systems with the participation of titanium, aluminium, chromium, iron, tungsten, nitrogen, oxygen, chlorine, which allowed to determine the influence of process parameters (reaction medium composition, temperature, pressure) on the phase and chemical compositions of coatings and set optimal parameters of the process. The temperature range of stable existence of chromium carbides, which can be offered as barriers, has been established.
It is established that on the studied alloys barrier layers can be obtained: by chromium plating, with the formation of chromium carbides layers (U8A steel); physical deposition from the gas phase of TiN (U8A steel, 9HS); nitriding followed by titanium alloying (U8A steel, VK8 hard alloy); formation of the TiN barrier layer during chromium aluminizing on BT6 titanium alloy.
The influence of barrier layers based on chromium carbides, titanium nitride on the structure, phase and chemical compositions of titanium-alloy, chromium-titanium alloy, chromium alloy coatings obtained on the surface of the studied alloys was investigated. The mechanisms of their formation are offered.
The physical-chemical properties of the obtained coatings were studied: micro-hardness, wear resistance, heat and corrosion resistance. The high micro-hardness of the obtained coatings was established due to the presence in their composition of chromium carbides layers, titanium, titanium nitride (13.0-35.6 GPa), intermetallics, oxides (1.9 - 12.6 GPa).
It is shown that the application of the investigated coatings leads to an increase of 1.8-6.9 times the wear resistance of the initial alloys under dry friction. The cutting properties of MNSP from VK8 alloy with coatings increase by 8.3 times.
It is established that the obtained coatings increase the heat resistance of U8A steel in an air atmosphere at 800 ° C and its corrosion resistance in industrially important aggressive environments (technical water, nitric and organic acid solutions). The mechanisms of protective action of coatings are determined. It is shown that the application of chromium aluminized coating leads to increased corrosion resistance of BT6 alloy in solutions of organic acids and hydrogen peroxide.
In the dissertation, new methods of obtaining coatings with a barrier component involving chromium carbides, titanium nitride are proposed. Coatings applied to the surface of VT6 titanium alloy, VK8 hard alloy were tested at Ukrainian enterprises.
Keywords: U8A carbon steel, 9HS alloy steel, VT6 titanium alloy, VK8 solid alloy, diffusion metallization, barrier layers, coatings, aluminizing, chroming, aluminium chroming, chromium-aluminizing, chromium titanium-aluminizing, phase composition, chemical composition, structure, micro-hardness, heat resistance, corrosion resistance, wear resistance in the conditions of friction and sliding.
