Self-fluxing Ni-based coatings (NiCrFeBSiC) were deposited through gas-flame spraying and evaluated in three conditions: as-sprayed, flame-remelted, and furnace-heat-treated (1025 °C/5 min). Phase analysis (XRD) revealed FeNi₃ together with strengthening carbides/borides (e.g., Cr₇C₃, Fe₂₃(C,B)₆); post-treatments increased lattice order. Cross-sectional image analysis showed progressive densification (thickness ~805 → 625 → 597 µm) and a drop in porosity from 7.866% to 3.024% to 1.767%. Surface roughness decreased from Ra = 31.860 to 14.915 to 13.388 µm. Near-surface microhardness rose from 528.7 ± 2.3 to 771.6 ± 4.6 to 922.4 ± 5.7 HV, while adhesion strength (ASTM C633) improved from 18 to 27 to 34 MPa. Wettability followed the densification trend, with the contact angle increasing from 53.152° to 79.875° to 89.603°. Under dry ball-on-disk sliding against 100Cr6, the friction coefficient decreased and stabilized (0.648 ± 0.070 → 0.173 ± 0.050 → 0.138 ± 0.003), and the counterbody wear-scar area shrank by ~95.6% (0.889 → 0.479 → 0.0395 mm²). Wear-track morphology evolved from abrasive micro-cutting (as-sprayed) to reduced ploughing (flame-remelted) and a polishing-like regime with a thin tribo-film (furnace). Potentiodynamic tests indicated the lowest corrosion rate after furnace treatment (CR ≈ 0.005678 mm·year⁻¹). Overall, furnace heat treatment provided the best structure–property balance (lowest porosity and Ra, highest HV and adhesion, lowest and most stable μ, and superior corrosion resistance) and is recommended to extend the service life of NiCrFeBSiC coatings under dry sliding.

In this study, the process of electrolytic–plasma nitrocarburizing (EPNC) of 20-grade steel was investigated using various electrolytes and temperature regimes. At the first stage, optical spectral analysis of plasma emission during EPNC was carried out with spectral registration in the range of 275–850 nm, which allowed the identification of active components (Hα, CN, Fe I, O I lines, etc.) and the calculation of electron density. Additionally, the EPNC process was recorded using a high-speed camera (1500 frames per second), which made it possible to visually evaluate the dynamics of arc and glow discharges under varying electrolyte compositions. At the next stage, the influence of temperature regimes (650 °C, 750 °C, and 850 °C) on the formation of the hardened layer was studied. Using SEM and EDS methods, the morphology, phase zones, and the distribution of chemical elements were determined. Microhardness measurements along the depth and friction tests were carried out. It was found that a temperature of 750 °C provides the best balance between the uniformity of chemical composition, high microhardness (~800 HV), and a minimal coefficient of friction (~0.48). The obtained results confirm the potential of the selected EPNC regime for improving the performance characteristics of 20-grade steel.

The study investigates the effect of plasma-electrolytic polishing on the structure and wear resistance of 30KhGSA steel after plasma-electrolytic boriding. Plasma-electrolytic boriding was carried out in a boron-containing electrolyte at a temperature of 900 °C, which ensured the formation of a hardened modified layer consisting of a surface oxide layer, a subsequent zone composed of boride phases FeB and Fe₂B, as well as a transitional martensitic zone. To remove brittle oxide phases and reduce surface roughness, plasma-electrolytic polishing in an alkaline solution was applied, which made it possible to form a smoother and more stable surface. The results showed that plasma-electrolytic boriding increases the microhardness up to 1500–1600 HV_0.1, which is 5–6 times higher compared to untreated steel, and reduces the friction coefficient and wear rate. However, the borided layers exhibit brittleness and surface roughness. Subsequent plasma-electrolytic polishing made it possible to reduce surface roughness by nearly an order of magnitude, decrease the friction coefficient by more than 30%, and almost halve the wear rate. The obtained results confirm the high potential of this combined technology for strengthening structural steel components operating under high loads and severe wear conditions.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ДИФФУЗИОННОЙ ЭЛЕКТРОЛИТНО-ПЛАЗМЕННОЙ ОБРАБОТКИ НА ТРИБОЛОГИЧЕСКИЕ ХАРАКТЕРИСТИКИ СТАЛИ 40Х

In this study, bioactive hydroxyapatite coatings were deposited on commercially pure Grade 2 titanium substrates by detonation spraying at different O₂/C₂H₂ ratios in the range of 2.6-3.7. X-ray diffraction analysis confirmed the predominance of the hydroxyapatite phase with partial formation of α-tricalcium phosphate, which is attributed to high temperatures and intense dynamic processes in the detonation jet. The formed coatings exhibit pronounced hydrophobicity, high structural heterogeneity, and a well-developed surface microrelief, promoting improved interaction with bone tissue and accelerated osseointegration. Tribological tests conducted under dry conditions and in Ringer’s solution demonstrated a significant increase in wear resistance compared to uncoated Grade 2 titanium. The best friction characteristics and the lowest wear volume were observed for coatings deposited at O₂/C₂H₂ ratios of 3.0 and 3.3, which is associated with an optimal combination of crystallinity, phase composition, and adhesion strength. Coatings formed under these conditions provide stable tribological behavior in physiological environments. The obtained results confirm the prospects of detonation-sprayed hydroxyapatite for improving the durability, biocompatibility, and operational reliability of titanium implants.

This paper presents the synthesis of silicon dioxide (SiO₂) from rice husk ash through chemical treatment followed by heat treatment at 800 °C for 3 h. The structural and physicochemical properties of the synthesized silica were investigated using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and laser diffraction particle size analysis. The synthesized silica exhibited an amorphous structure, with a median particle size (D50) of approximately 88.9 μm. Subsequent annealing at 1200 °C led to crystallization of the silica, resulting in the formation of quartz and cristobalite phases. FTIR analysis revealed characteristic absorption bands associated with Si–O–Si stretching vibrations in the 1000–1100 cm⁻¹ region, as well as bands attributed to hydroxyl groups. The obtained crystalline silica materials demonstrate potential for use as powder materials in thermal spraying technologies.