Olga V. Krysina

The work is aimed to study the features of the formation of the surface layer of samples after combined treatment, including vacuum-arc deposition of titanium nitride coatings on silumin of eutectic composition and subsequent treatment of the “nitride coating/silumin substrate” system with a pulsed electron beam of submillisecond duration. Detailed studies of samples treated with an electron beam according to optimal modes were carried out by the transmission electron microscopy methods. Peculiarities of the structure and phase composition of the system were revealed depending on the electron beam processing mode. The treatment according to the optimal electron beam treatment modes to obtain the surface layer of the “TiN coating/silumin substrate” system with high wear resistance, adhesion and hardness does not exceed the temperature of 1150°C and does not lead to destruction of the coating according to TEM analysis results. The coating consists of nanosized TiN and Ti₂N crystallites, which are combined into columns with subnanometer transverse dimensions. The electron beam treatment of the “TiN coating/silumin substrate” system leads to the formation of a cellular crystallization structure, where aluminum-based cells are separated from each other by silicon-based particles with nano-sized dimensions. The system has high properties: hardness HV ≈ 2 GPa, wear parameter ≈1 × 10^–4 mm³ N^–1 m^–1 and high adhesion strength (L > 2.5 N).

Сформированы многослойные металлокерамические покрытия на основе высокоэнтропийного сплава элементного состава TiNbZrTaHf путем осаждения на твердотельную подложку в вакууме из многокомпонентной газо-металлической плазмы, созданной вакуумно-дуговым испарением многоэлементного катода в режиме с плазменным ассистированием в среде смеси газов азот-аргон. Показано, что покрытия являются нанокристаллическим (2,5–4 нм) материалом. Методами рентгенофазового анализа показано, что керамический слой является двухфазным (TiNbZrTaHf)N + Ta4N). Нитрид (TiNbZrTaHf)N имеет гранецентрированную кубическую кристаллическую решетку с параметром решетки а = 4,4465 Å (D = 22 нм; Δd/d = 7·10–3).Нитрид Ta4N имеет тетрагональную кристаллическую решетку с параметрами решетки а = 6,8272 и c = 4,1697 Å (D = 10 нм; Δd/d = 7·10–3). Металлический слой имеет объемно-центрированную кубическую кристаллическую решетку (а = 0,33396 нм). Выявлено формирование переходных слоев между подложкой и металлическим слоем, между металлическим и керамическим слоями. Твердость покрытия составила 36,7 ГПа, модуль Юнга 323 ГПа, параметр износа покрытия k = 2,9·10–5 мм3/Н·м, коэффициент трения μ = 0,71. Стоит отметить перспективность использования покрытий на основе ВЭС в качестве защитных покрытий для инструмента и деталей широкого круга применений.

Multilayer cermet coatings based on a TiNbZrTaHf high-entropy alloy were produced on solid substrates by plasma-assisted vacuum-arc deposition. The assisting multicomponent metal-gas plasma was generated by evaporating TiNbZrTaHf cathodes in a gas mixture of nitrogen and argon. It was found that the coatings were nanocrystalline in structure (with nanocrystal sizes ranging from 2.5 to 4 nm). The metallic layer had a body-centered cubic lattice (a = 0.33396 nm), and the ceramic layer had a face-centered cubic lattice (a = 0.44465 nm). Transition layers formed between the substrate and the metallic layer and between the metallic and the ceramic layers were revealed. The hardness of the coatings was 36.7 GPa and their Young’s modulus was 323 GPa.

The paper analyzes the structure and properties of metal, cermet, and ceramic NbMoCrTiAl high-entropy alloy (HEA) coatings formed on solid substrates by plasma-assisted vacuum arc deposition (from multicomponent gas-metal plasma through Nb, Mo, Cr, and TiAl cathode evaporation in argon and/or a mixture of argon and nitrogen). The analysis shows that all coatings represent a nanocrystalline (3–5 nm) multilayer film. The metal coating has a bcc lattice (a = 0.3146 nm). The ceramic coating has an fcc lattice (an uncertain lattice parameter due to highly smeared diffraction peaks). The coating hardness increases in the order of metal, cermet, and then ceramic, reaching 43 GPa at Young’s modulus equal to 326 GPa. When heated in air, the metal and cermet coatings start to oxidize at 630–640 °C, and the ceramic coating at 770–780 °C.

Complex alloying, combining in a certain sequence the saturation of surface layer of material with atoms of metals and gases, is now widely used in most industrialized countries of the world. The present work is devoted to the revelation and analysis of dependences of element and phase composition, defect substructure, mechanical (microhardness) and tribological (wear resistance and friction coefficient) properties changes of alloying carbon steel subjected to combined treatment including the saturation of the sample surface layer by aluminum and subsequent nitriding. The material used for the study was AISI 5135 steel, which in the initial state has a structure represented by ferrite grains and pearlite grains of lamellar morphology. The combined modification was carried out in a single vacuum space on the TRIO setup with the chamber dimensions of 600×600×600 mm³ equipped by switching unit for realization of elion (electron and ion) mode of treatment. Aluminizing was carried out at the temperature of 963 К during 4 h. The cathode of electroarc evaporator was made of A7 grade aluminum alloy (98.8 % Al). Subsequent nitriding of aluminized layer was carried out at the temperature of 803 К during 2 h. It was established that the modified layer with the thickness of 70 μm is formed as a result of the combined treatment. It is demonstrated that the combined steel modification is accompanied by the formation of multiphase submicro- and nanostructure state including aluminum nitrides, iron and chromium nitrides and aluminides. It is revealed that the steel hardness is maximal on the modification surface and it exceeds by 3 times that of the initial steel. Wear resistance under the dry conditions decreases after the combined modification.

This paper presents a study of a combined modification of silumin, which included deposition of a ZrN coating on a silumin substrate and subsequent treatment of the coating/substrate system with a submillisecond pulsed electron beam. The local temperature on the samples in the electron-beam-affected zone and the thickness of the melt zone were measured experimentally and calculated using a theoretical model. The Stefan problem was solved numerically for the fast heating of bare and ZrN-coated silumin under intense electron beam irradiation. Time variations of the temperature field, the position of the crystallization front, and the speed of the front movement have been calculated. It was found that when the coating thickness was increased from 0.5 to 2 μm, the surface temperature of the samples increased from 760 to 1070 °C, the rise rate of the surface temperature increased from 6 × 10⁷ to 9 × 10⁷ K/s, and the melt depth was no more than 57 μm. The speed of the melt front during the pulse was 3 × 10⁵ µm/s. Good agreement was observed between the experimental and theoretical values of the temperature characteristics and melt zone thickness.