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.

The work is devoted to the study of the features of the formation of modified surface layers in the electrolytic-plasma coating of the surface of 20GL steel used for the manufacture of parts of a railroad train. The results of the investigation of the effect of the electrolytic-plasma coating on the morphology and the structural-phase state of the surface, the dislocation structure of 20GL steel before and after treatment are presented. It has been established that in the initial state 20GL steel has a ferrite-pearlite structure, and after the electrolytic-plasma coating of the surface, a lamellar structure of perlite and ferrite is observed. It is found that in the initial state 20GL steel has the following average parameters of the fine structure: 〈ρ〉 = 2.41 × 10¹⁰ cm^–2, 〈ρ_±〉 = 2.23 × 10¹⁰ cm^–2, 〈χ〉 = 〈χ_lp〉 + 〈χ_elas〉 = 560 + 25 = 585 MPa, 〈σ_l〉 = 310 MPa, 〈\({{\sigma }_{{\text{d}}}}\)〉 = 〈\(\sigma _{{\text{d}}}^{{{\text{pl}}}}\)〉 + 〈\(\sigma _{{\text{d}}}^{{{\text{elas}}}}\)〉 = 300 + 35 = 335 MPa; and after processing, the average parameters of the fine structure changed as follows: 〈ρ〉 = 1.03 × 10¹⁰ cm^–2, 〈ρ_±〉 = 0.82 × 10¹⁰ cm^–2, 〈χ〉 = 〈χ_pl〉 = 205 MPa, 〈σ_l〉 = 200 MPa, 〈\({{\sigma }_{{\text{d}}}}\)〉 = 〈\(\sigma _{{\text{d}}}^{{{\text{pl}}}}\)〉 = 175 MPa.

In recent decades, great efforts have been made to significantly improve the performance characteristics of high-speed steel using various surface hardening techniques. Electron beam modification is engaging because it has an exceptionally high thermal efficiency and can significantly improve steels’ physical and mechanical properties. This work is devoted to researching the fine structure and changing the structural phase state of the surface layer of R6M5 high-speed steel after exposure to an electron beam. Electron beam treatment of steel R6M5 was carried out on a vacuum installation. The structure and phase composition of P6M5 steel samples were studied by transmission electron microscopy. Determined that after electron irradiation, the steel structure as in the initial state consists of martensite, carbides and residual austenite. After electron irradiation, an increase in the volume fraction of lamellar martensite is observed: the fraction of lamellar martensite in the initial state is 80%, and after irradiation, it is ~90% of the total fraction of α′-martensite. The action of the electron beam led to an increase in internal stresses in α′-martensite. Revealed, the value of the scalar dislocation density in R6M5 steel after exposure to an electron beam is higher than in the initial state. A cardinal difference in the state of the material after exposure to an electron beam is the presence of bending extinction contours in all M₆C carbide particles.