The paper considers the combined effect of polysaccharides (carboxymethyl cellulose and carboxymethyl starch) with sodium silicate in the f lotation of talcose copper-nickel ore. The analysis of the f lotation results and the assessment of hydrophobicity and surface charge of minerals showed that the composition of carboxymethylated  polysaccharides  and  sodium  silicate  hydrophilizes  the talc surface more effectively than each of the reagents separately. Moreover, sodium silicate alone hardly depresses the talc surface at all. The depression of f lotation-active silicates is effective when polysaccharide and sodium silicate are sequentially supplied. Under these conditions, sodium silicate makes a significant contribution to increasing the negative charge on the talc particles surface. The effect is more pronounced for compositions with starch, characterized by a lower degree of substitution compared to cellulose. It results in a significantly reduced recovery of f lotation-active magnesium-containing silicates and a slight decrease in sulfide recovery. To determine the features of the mechanism of talc and sulfide minerals depression in f lotation, we performed calculations using the extended DLVO theory based on the obtained values of the zeta potential and force of detachment. We established that sulfide minerals have no potential barrier preventing their interaction with an air bubble, regardless of the compositions of the studied depressants used. We propose the following interaction mechanism: when sodium silicate is supplied first, the talc basal surface is very insignificantly hydrophilized as SiO(OH)^– ions are not easy to fix. On the contrary, when the carboxymethylated polysaccharide is supplied first, significant hydrophilization of the talc surface with carboxyl groups occurs due to the hydrophobic interaction between the corresponding regions of the macromolecule and the talc basal surface.

Using keyhole plasma arc welding, welded joints of a Ti₂AlNb-based alloy, VTI-4, were obtained, and their structure and mechanical properties were studied. It has been established that the dynamic effect of a keyhole arc had a positive effect on the quality of the welded joint; namely, lack of penetration, porosity, and microcracks were eliminated. The welded joint consisted of a fusion zone (FZ), a heat-affected zone (HAZ), and a base metal (BM). Depending on the phase composition and morphology of the obtained phases, the HAZ can be divided into four zones: HAZ1 with large β-phase grains near the melting line, HAZ2 with large β-phase grains + α₂, HAZ3 with more fragmented β-phase grains retaining more α₂-phase, and HAZ4 with the phase composition β + α₂ + O. Subsequent heat treatment (HT: quenching at 920 °C for 2 h, cooling in air, followed by aging at 800 °C for 6 h, cooling in air) preserved the zone structure of the weld but led to the formation of the O-phase within β-grains. The microhardness of the weld in the zone corresponds to 360±15 HV0.2, but after HT, it increased to 382±20 HV0.2. The strength properties of the welded joint after HT were above 90 % of the base metal (σ_ucs = 1120 MPa, σ_0.2 = 1090 MPa), while elongation to failure is close to the initial condition (δ = 2.1 %).

The composite materials based on the Al–Si system alloys, strengthened with a highly dispersed titanium carbide phase, possess improved characteristics and belong to the group of promising structural materials. Currently, self-propagating high-temperature synthesis (SHS) based on the exothermic interaction, wherein titanium and carbon precursors directly involve in the melt, is the most accessible and effective method to obtain them. This paper proves the feasibility and demonstrates the successful synthesis of a 10 wt.% titanium carbide phase in the melt of the AK10M2N alloy, resulting in the AK10M2H-10% TiC composite material. Samples of the matrix alloy and the composite material were subjected to heat treatment according to the T6 mode, with various temperature-time parameters for hardening and aging operations. Based on the results, optimal heat treatment modes were selected to ensure maximum hardness. We studied the macroand microstructure of the obtained samples and performed micro X-ray spectral and X-ray diffraction phase analyses. Different groups of properties underwent comparative tests. It was established that the density of AK10M2N–10%TiC samples before and after heat treatment, according to optimal modes, is close to the calculated value. We showed that the combination of reinforcement and heat treatment significantly increases hardness, microhardness, and compressive strength, with a slight decrease in ductility. Additionally, it maintains the values of the coefficient of thermal linear expansion, high-temperature strength, and resistance to carbon dioxide and hydrogen sulfide corrosion at the level of the original alloy. The greatest effect was observed during the investigation of tribological characteristics: heat treatment of the composite material according to the recommended mode significantly reduces the wear rate and friction coefficient, eliminates seizure and tearing, and prevents temperature rise due to friction heating.

As part of the study, the influence of yttrium content on the properties of particles during controlled precipitation and after thermal treatment was investigated. Precipitation was carried out at a constant pH of 5 from nitric acid solutions, where the concentration of zirconium was 1 mole/dm³ and the yttrium content ranged from 0 to 30 % based on their oxides. The drying and calcination temperatures of the precipitates were 40 °C and 1000 °C, respectively. It was shown that with a yttrium content of up to 15 %, there was a consistent increase in the average diameter of zirconium hydroxide particles during deposition. When the yttrium concentration was increased to 30 %, the average particle size increased during the first 10 minutes of deposition, followed by a gradual decrease. The largest particle diameter was observed in the specimen with 7 % yttrium. In all cases, the formation of spherical aggregates was observed. With an increasing yttrium content, the boundaries between particles became smoother, and the degree of co-deposition of yttrium during synthesis decreased from 80 % to 60 %. Depending on the yttrium concentration, different modifications of stabilized zirconium dioxide powders were obtained: tetragonal ZrO₂ for 2–7 % yttrium, and cubic ZrO₂ for 15–30 % yttrium. Therefore, the results obtained during the study can be useful for the development of technology for the production of powdered materials for various applications.

The electrodes for electrospark deposition (ESD) were fabricated from hot-pressed blanks composed of a mechanically alloyed powder mixture of R6M5K5 high speed steel. This mixture was enriched with a 40 % addition of heat-resistant MoSi₂–MoB–HfB₂ ceramics, produces through the self-propagating high-temperature synthesis method (resulting in the R6M5K5-K electrode), as well as variant without any ceramic addition (resulting in the R6M5K5 electrode). We examined both the composition and structure of the electrode materials and the coatings derived from them, identifying the characteristics of mass transfer from hot-pressed electrodes to substrates of 5KhNM die steel under various frequencies and energy conditions during processing. The R6M5K5 electrode consists of an α-Fe-based matrix incorporating dissolved alloying elements and contains discrete particles of ferrovanadium, tungsten carbide, and molybdenum. The R6M5K5-K electrode, in addition to the α-Fe-based matrix, includes borides and carbides, as well as hafnium oxide. The use of the R6M5K5 electrode resulted in a consistent weight increase in the cathode throughout the entire 10-minute processing period. In contrast, the application of the ceramicenhanced electrode led to weight gain only during the initial 3 min of processing. Subsequently, ESD produced coatings of 22 and 50 μm thickness on the surface of 5KhNM steel using R6M5K5 and R6M5K5-K electrodes, respectively. The introduction of SHS ceramics escalated the roughness (Ra) of the surface layers from 6 to 13 μm and the hardness from 9.1 to 15.8 GPa. The coating from the R6M5K5 electrode was composed of austenite (γ-Fe) and exhibited high uniformity. Conversely, the coating from the R6M5K5-K electrode consisted of a diverse matrix with both crystalline and amorphous iron, an amorphous phase rooted in the Fe–B alloy, and scattered phases of HfO₂, HfSiO₄, Fe₃Si, and Fe₃B. High-temperature tribological testing at 500 °C in an air atmosphere showed that the coatings possess a friction coefficient of 0.55–0.57 when coupled with a counterbody of AISI 440C steel. The integration of heat-resistant ceramics notably enhanced the coating's wear resistance, increasing it by a factor of 13.5.

The paper investigates the impact of Mn content (Mn = 0; 0.5; 0.6; 1; 1.5 at.%) in the composition of the electrodes of the Al–Ca–Mn system on the structure and properties of electrospark coatings formed on LPBF substrates made of EP741NP alloy. It was found that the highest weight gain of the substrate (5.8·10^–4 g) was recorded when the Al–7%Ca–1%Mn electrode with a low degree of supercooling of the melt (Δt = 5 °C) was subject to electrospark treatment (EST). EST with this electrode with a fine eutectic structure enables the formation of coatings with minimal surface roughness (Ra = 3.51±0.14 μm). The nanocrystalline structure of the coatings was confirmed by transmission electron microscopy, including HRTEM. Comparative tribological tests revealed that the coating with maximum hardness (10.7±0.8 GPa) formed during EST with an electrode containing 1.5 at.% Mn had the minimal wear rate (1.86 ·10^–5 mm³/(N· m)). We proved that EST with Al–Ca–Mn electrodes enables to reduce the specific weight gain of the LPBF EP741NP alloy during isothermal (t = 1000 °C) curing in air due to in situ formation of a complex thermal barrier layer consisting of oxides (α-Al₂O₃, CaMoO₄) and intermetallides (γ ′-Ni₃Al and β-NiAl). We determined the concentration limit of Mn (1.0 at.%) in the electrode, at which the barrier layer retains its integrity and functionality.

(08.06.1924 – 30.09.2014)