Titanium and its alloys are widely used in biomedical implants due to their favorable mechanical properties and corrosion resistance; however, their natural surface lacks sufficient bioactivity and antibacterial performance. Micro-arc oxidation is a promising approach to producing bioactive coatings, and the incorporation of nanoparticles such as TiO₂ may further improve their functionality. This study aimed to determine the optimal TiO₂ nanoparticle concentration in the micro-arc oxidation electrolyte that ensures coating stability and biological safety. Calcium–phosphate coatings were fabricated on commercially pure titanium using micro-arc oxidation with two TiO₂ concentrations: 0.5 wt.% (MAO 1) and 1 wt.% (MAO 2). Surface morphology, porosity, and phase composition were analyzed by scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. Corrosion resistance was evaluated via potentiodynamic polarization in NaCl and Ringer’s solutions, while biocompatibility was assessed in vitro using HOS human osteosarcoma cells and MTT assays. Increasing the TiO₂ content to 1% decreased coating porosity (13.7% vs. 26.3% for MAO 1), enhanced corrosion protection, and reduced the friction coefficient compared to bare titanium. However, MAO 2 exhibited high cytotoxicity (81% cell death) and partial structural degradation in the biological medium. MAO 1 maintained integrity and showed no toxic effects (3% cell death). These results suggest that 0.5% TiO₂ is the optimal concentration, providing a balance between corrosion resistance, mechanical stability, and biocompatibility, supporting the development of safer implant coatings.

This article examines the theoretical aspects of thermal processes occurring during electrolytic-plasma hardening (EPH), including the analysis of temperature fields and heating rates. The finite difference method was used for numerical modeling, allowing for a more precise determination of the temperature distribution in the treated material. The heat transfer problem in a flat plate with a thickness of 15 mm was considered, where the boundary conditions were as follows: on one boundary, heating was carried out by a surface thermal flux from the electrolyte plasma, while on the opposite side, heat was dissipated through convection in an air medium. The calculations revealed non-uniform temperature distribution over time and depth, confirming the formation of three distinct structural zones: the hardened zone, the heat-affected zone, and the base matrix. The temperature of the samples during the experiment was measured using a thermocouple positioned 2 mm from the heated surface. Experimental data obtained from the treatment of 45 steel samples confirmed the accuracy of the numerical modeling. The research results demonstrate the effectiveness of numerical modeling, including the finite difference method, in optimizing EPH parameters, thereby reducing the volume of experimental work and lowering technology development costs. The obtained data can be used to improve surface hardening technologies for structural steel components used in agricultural machinery, mechanical engineering, and other industries. The study confirms the potential of EPH for enhancing the operational characteristics of steel products.

This article presents a comprehensive examination of the electrolytic-plasma hardening (EPH) process applied to 20GL structural steel, a material frequently used in the automotive, transport, and various other industries. The relevance behind this research lies in the necessity to enhance the performance of steels that face high mechanical loads, elevated temperatures, and corrosive environments. Experimental findings reveal that electrolytic-plasma treatment substantially increases the hardness of 20GL steel to approximately 600 HV on average. Additionally, prolonging the heating duration contributes significantly to greater hardness, playing a decisive role in bolstering wear resistance under load. Microstructural analysis confirms the formation of a fine-grained martensitic phase, highlighting the steel’s transformation and strengthening. Furthermore, the study emphasizes that the chemical composition of 20GL steel influences the hardness gradient from the surface inward and leads to the development of finer-grained features in the steel’s microstructure. Overall, the electrolytic-plasma process proves beneficial not only for improving mechanical attributes but also for enhancing reliability and service life of critical components. From an industrial standpoint, this technology is notable for its adaptability and cost-effectiveness, making it an attractive solution for sectors such as automotive manufacturing, construction, and the energy industry. Thus, electrolytic-plasma hardening emerges as a forward-looking method aligned with modern engineering demands, offering a promising avenue for advanced material optimization.