Arc spraying is one of the most effective and cost-efficient thermal spraying technologies for creating high-quality protective coatings. This paper examines the influence of arc spraying process parameters on the properties of steel coatings. The parameters varied in this study included gas pressure, wire feed rate, and the distance from the spray gun to the substrate (standoff distance). Experimental evaluations focused on surface roughness, thickness, porosity, structure, and hardness of the coatings. The techniques used for these evaluations included profilometry for roughness measurement, scanning electron microscopy (SEM) for structural analysis, Vickers hardness testing, and optical microscopy. The results demonstrate a significant influence of arc spraying parameters on the characteristics of the resulting coatings. The analysis revealed that the coatings produced under different modes exhibit a layered structure and vary in thickness. A detailed examination of the coating structure identified defects such as unmelted particles, voids, and delamination in the interface zone. The study of coating thickness and porosity showed that increasing the wire feed rate and decreasing the standoff distance leads to the formation of thicker and denser coatings. Specifically, increasing the wire feed rate from 2 to 12 cm/s resulted in a decrease in porosity from 12.59% to 4.33% and an increase in coating thickness to 699 μm. The surface analysis highlighted the importance of a comprehensive approach to selecting the optimal roughness. While increasing the wire feed rate up to 12 cm/s can increase the Ra roughness parameter, gas pressure also significantly influences this parameter, reducing roughness from Ra = 18.63 μm at 6 MPa to Ra = 15.95 μm at 8 MPa. Additionally, it was found that varying the arc spraying parameters affects the hardness of the coatings, with all modes resulting in hardness values higher than that of the substrate. Therefore, optimizing these parameters enables the achievement of the best combination of mechanical and structural properties in the coatings. These findings can be valuable for further improvement of arc spraying technologies and the expansion of their application across various industries.

In this study, a surface hardening of AISI 52100 bearing steel was performed by ultrasonic nanocrystal surface modification (UNSM), and electrolytic-plasma thermo-cyclic surface modification (EPSM), and their effects on the wear resistance were investigated. To evaluate the impact of these treatments on the wear resistance, the friction tests under dry conditions were conducted using a ball-on-disk tribometer in accordance with ASTM G99. The microstructure of the samples before and after treatment was characterized by scanning electron microscopy. The micro-hardness with respect to the depth from the top surface was measured using a Vickers micro-hardness tester. Microstructural observations showed that EPSM treatment led to the formation of residual austenite in the surface layer, while UNSM treatment led to the formation of a surface severe plastic deformation layer on the surface of the samples. The increase in the micro-hardness of the treated layer was confirmed after UNSM at room temperature and after EPSM at different cycles. The highest increase in wear resistance was observed for the specimen treated by UNSM treatment at 700 °C and five cycles of EPSM treatment. In addition, the wear volume, which has correlation with the friction coefficient and hardness, was determined.

Samples using powders of four different fractions, 15–20 μm, 20–30 μm, 30–40 μm and 40–45 μm, were fabricated to investigate the wear resistance, corrosion resistance and tribological properties of the 86WC-10Co-4Cr coating obtained using the HVOF method. The phase composition, microstructure and elemental distribution were analyzed using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy techniques. The hardness was measured on a Vickers microhardness tester, the friction coefficient and wear rate were investigated using a tribometer, and the corrosion resistance was evaluated on an electrochemical corrosion station. The results showed that the cross-sectional microstructure of the coating is mainly represented by multifaceted WC crystals embedded in the Co-Cr matrix and the presence of lower tungsten carbides, particularly W₂C. The 15–20 μm fraction particles were subjected to superheating, contributing to the decarburization process. The 20–30 µm and 30–40 µm sized particles prevented overheating and had a more homogeneous structure. The 40–45 µm powder fractions did not reach sufficient temperature for complete melting, resulting in the formation of pores in the coating layers. The phase composition of the coatings included WC, W₂C and CoO phases. According to the results of the study, it was found that the optimal powder fraction for coating the 86WC-10Co-4Cr composition with improved characteristics is the fraction of the 20–30 µm sized particles.

This paper studies the coatings deposited on a 65G steel substrate by electric arc metallization using a 30KhGSA wire. The properties of the coatings obtained at 30 V, 40 V and 45 V are discussed, including their microstructure, porosity, microhardness, coefficient of friction and corrosion resistance. The experiments showed that the coatings possess a layered structure formed by sequential deposition of metal microdroplets. It was found that the increase in voltage favors the decrease in porosity, increase in layer density, increase in microhardness and improvement in wear resistance and corrosion resistance. At maximum voltage (45 V), there are optimum performance characteristics, such as minimal porosity (1.36%), high microhardness (305 HV) and improved corrosion resistance. The main defects of the coatings, including pores and oxide inclusions, which are formed during the sputtering process and depend on the kinetic energy of the microdroplets, were identified. These defects affect the mechanical and protective properties of the coatings.

This study investigated the influence of electrofrictional treatment on the structure and hardness of the surface layers of the 40Kh and 65G steels. Based on the results of scanning electron microscopy, it was determined that during the electrofrictional hardening (EFH) of 40Kh steel, a hardened surface layer, with a microhardness of 873 ± 37 HV0.1, was formed. This layer consisted of two zones: a surface-quenched zone, with a structure of fine needle-like martensite and austenite; and a heat-affected zone (transition layer), with a structure of martensite and high-dispersion pearlite (troostite), smoothly transitioning into the original ferrite–pearlite structure. After EFH, a layer with a thickness of ~150 μm containing carbides in the martensite was formed on the surface of the 65G steel, which smoothly transitions into the heat-affected zone with a structure of needle-like martensite. The microhardness of the 65G steel in its initial state was 277 ± 20 HV0.1, and after EFH, it reached 811 ± 23 HV0.1. The results of the microstructure analysis of the 40Kh and 65G steels after EFH were consistent with the results of X-ray phase analysis. It was established that the phase composition of the 40Kh and 65G steels in their initial states consisted of an α-Fe phase with a body-centered cubic (BCC) lattice, and after EFH, both steels formed strengthening phases: residual austenite (γ-Fe) and martensite (α′-Fe). During EFH, under high temperature and pressure conditions, carbon from the cast iron electrode was alloyed with iron, contributing to the formation of cementite on the surface of the 65G steel. These obtained data allowed us to conclude that electrofrictional treatment is an effective method for the surface hardening of 40Kh and 65G steels.

The development of power engineering requires the introduction of new materials and technologies to improve the quality and durability of products. One promising direction is the creation of heat-protective coatings for the protection of working surfaces of turbine blades of gas turbine engines operating at temperatures up to 1000–1200 °C. Intermetallic coatings based on iron aluminides (Fe₃Al, FeAl) have high resistance to oxidation due to the formation of an oxide layer: Al₂O₃. However, their application is limited by brittleness due to the so-called third element effect, which can be reduced through alloying with chromium. In this study the processes of formation of Fe–Al–Cr intermetallic coatings produced by air plasma spraying and the mechanisms affecting their stability at high temperatures were investigated. Experimental studies included the analysis of the microhardness, wear resistance, and corrosion resistance of coatings, as well as their phase composition and microstructure. The results showed that the optimization of sputtering parameters, especially in the FrCrAl (30_33) mode, promotes the formation of a coating with improved tribological and anticorrosion characteristics, which is associated with its dense and uniform structure. These data have an important practical significance for the creation of wear-resistant and corrosion-resistant coatings applicable in power engineering.