In this work, bioceramic coatings were formed on Ti6Al4V titanium alloy using a combined technique of plasma electrolytic oxidation followed by gas detonation spraying of calcium phosphate ceramics, based on hydroxyapatite. Plasma electrolytic oxidation was carried out in electrolytes with various chemical compositions, and the effect of electrolytes on the macro and microstructure, pore size and phase composition of coatings was estimated. Three types of electrolytes based on sodium compounds were used: phosphate, hydroxide, and silicate. Plasma electrolytic oxidation of the Ti–6Al–4V titanium alloy was carried out at a fixed DC voltage (270 V) for 5 min. The sample morphology and phase composition were studied with a scanning electron microscope and an X-ray diffractometer. According to the results, the most homogeneous structure with lower porousness and many crystalline anatase phases was obtained in the coating prepared in the silicate-based electrolyte. A hydroxyapatite layer was obtained on the surface of the oxide layer using detonation spraying. It was determined that the appearance of α-tricalcium phosphate phases is characteristic for detonation spraying of hydroxyapatite, but the hydroxyapatite phase is retained in the coating composition. Raman spectroscopy results indicate that hydroxyapatite is the main phase in the coatings.

This article analyzes the effect of electrolytic plasma nitriding on the performance of medium-carbon steel 45 under increased mechanical loads and in aggressive environments. Nitrided samples in carbamide electrolytes, both with and without the addition of ammonium nitrate, were compared to the initial material. SEM with EDX and XRD analysis was used to examine the microstructure and phase composition of nitrided samples. Wear resistance was studied using the ‘ball-on-disk’ method and Vickers microhardness testing, while corrosion resistance was studied using potentiodynamic polarization curves. The study results show that the sample without ammonium nitrate demonstrated better mechanical and corrosion properties due to a more homogeneous and denser nitride layer, approximately 10 µm thick, containing phases FeN and Fe₄N. Its wear resistance doubled compared to that of the initial sample. The sample treated in an electrolyte with the addition of ammonium nitrate demonstrated a higher current density (2.8672 × 10⁻⁵ A/cm²) and a lower corrosion potential (−0.565 V) compared to the initial sample (i_corr = 1.8971 × 10⁻⁵ A/cm², E_corr = −0.480 V) and the sample without ammonium nitrate (i_corr = 1.7315 × 10⁻⁵ A/cm², E_corr = −0.376 V). This is due to the formation of an uneven nitride layer and the presence of microcracks on the surface.

This study is aimed at obtaining a coating of aluminum oxide containing α-Al₂O₃ as the main phase by detonation spraying, as well as a comparative study of the structural, tribological and mechanical properties of coatings with the main phases of α-Al₂O₃ and γ-Al₂O₃. It was experimentally revealed for the first time that the use of propane as a combustible gas and the optimization of the technological regime of detonation spraying leads to the formation of an aluminum oxide coating containing α-Al₂O₃ as the main phase. Tribological tests have shown that the coating with the main phase of α-Al₂O₃ has a low value of wear volume and coefficient of friction in comparison with the coating with the main phase of γ-Al₂O₃. It was also determined that the microhardness of the coating with the main phase of α-Al₂O₃ is 25% higher than that of the coatings with the main phase of γ-Al₂O₃. Erosion resistance tests have shown (evaluated by weight loss) that the coating with α-Al₂O₃ phase is erosion-resistant compared to the coating with γ-Al₂O₃ (seen by erosion craters). However, the coating with the main phase of γ-Al₂O₃ has a high value of adhesion strength, which is 2 times higher than that of the coating with the main phase of α-Al₂O₃. As the destruction of coatings by the primary phase, α-Al₂O₃ began at low loads than the coating with the main phase γ-Al₂O₃. The results obtained provide the prerequisites for the creation of wear-resistant, hard and durable layered coatings, in which the lower layer has the main phase of γ-Al₂O₃, and the upper layer has the main phase of α-Al₂O₃.

The high-strength, medium-carbon alloy construction steel 40 Kh is commonly used in the manufacture of tools and machine parts. This paper experimentally investigates the effect of electrolytic plasma thermocyclic hardening on the surface hardening and microstructure modification of 40 Kh steel. The research was carried out using optical microscopy, scanning electron microscopy, X-ray diffraction analysis and micro-hardness measurements. Modified samples were obtained at different electrolyte plasma thermal cycling modes. As a result of the heat treatment, hardened layer segments of different thicknesses and structural composition formed on the surface of the steel. The parameters and mechanisms of surface hardening were determined by examining the microstructural modification and phase transformation both before and after treatment. It was revealed that the main morphological structural-phase component of the initial state of 40 Kh steel was a ferrite–pearlite structure, and after electrolytic plasma thermocyclic hardening, the hardened martensite phase was formed. It was found that in order to achieve a hardening depth of 1.6 mm and an increase in hardness to 966 HV, the optimum time for electrolytic plasma treatment of 40 Kh steel was 2 s. The technology under discussion gives an insight into the surface hardening potential for improving the service life and reliability of 40 Kh steel.

Electrolytic plasma thermocyclic surface hardening is an attractive solution for both chemical and heat treatment used to improve the properties of the steel surface by structural and phase transformation. Structural and phase transformations occurring during the process of electrolytic plasma thermocyclic hardening are performed repeatedly at varying heating–cooling temperatures, which radically improve the quality of the part and give them properties unattainable by means of one-time processing. The impact of electrolytic plasma thermocyclic hardening modes on the structure and mechanical and tribological properties of 30CrMnSiA steel is investigated. The structural and phase components were examined using optical and scanning electron microscopy, as well as X-ray phase analysis. It is established that the structure of the cross-section is characterized by the following zonality: zone 1—a near-surface hardened zone, which is composed of hardened martensite; zone 2—thermal influence; and zone 3—a matrix consisting of pearlite and ferrite. The microhardness and wear resistance of the hardened surface were evaluated by nanoindentation and “ball on disk” methods, respectively. Nanoindentation analysis demonstrated that the indentation hardening process provides a maximum increase in hardness by three times and an increase in stiffness with a decrease in the elastic modulus by 38% compared to the original steel. The results of tribological studies show that electrolytic plasma thermocyclic hardening increases the resistance of steel to friction by increasing the surface hardness and reduces the area of actual contact during friction. It is established that the microhardness of the cross-section decreases proportionally from the surface to the depth of the layer, which is associated with a decrease in the volume content of martensite.

In this work, the influence of the technological parameters of the detonation method on the formation of metal oxide compounds on the basis of titanium was investigated. The aim of the work was to investigate the method of the effective control of the phase composition and microstructure of titanium-based coatings during detonation spraying. The main parameters that varied in detonation spraying were the volume of filling the detonation barrel with explosive mixture and the oxygen/fuel ratio. The mechanism of formation of the gradient structure of coatings based on metal oxide compounds depending on the technological parameters of detonation spraying was considered. The structural-phase states and tribological properties of detonation coatings were investigated by the following methods: X-ray phase analysis (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX-mapping), profilometry, and the test for wear-resistance according to the “ball-disk” scheme. It is shown that the phase composition of coatings may significantly change relative to the initial titanium powder during the detonation spraying due to the interaction of particles of powders with components of the gas atmosphere. Varying the spraying parameters may control the chemical reaction and provide conditions for the synthesis of the desired phases in the coatings (titanium oxide TiO₂ and Ti₂O₃).