In this paper, we studied the formation of ultrafine and nanocrystalline core–shell structures based on refractory compounds of titanium with nickel during plasma-chemical synthesis of a mechanical mixture of TiC and TiNi in a low-temperature nitrogen plasma. Cooling took place in an intensely swirling nitrogen flow in a quenching chamber. The derived products were separated in a vortex-type cyclone and a bag-type fabric filter. After processing, the products were subjected to encapsulation aimed at reducing the pyrophoricity for long-term storage of the resulting finely dispersed powders under normal conditions. X-ray diffraction and high-resolution transmission electron microscopy were used to study the resulting powder products of plasma-chemical synthesis, and density measurements were conducted. Additionally, to define the average particle size more accurately, the specific surface was measured using the BET method. The instrumental research revealed the presence of ultra- and nanodispersed particles with a core–shell structure in the powder products. These particles included titanium carbide-nitride compounds as a refractory core and metallic nickel as a metallic shell. In addition, the presence of complex titanium-nickel nitride Ti_0.7Ni_0.3N was recorded. According to direct measurements, the average particle size of the nanocrystalline fraction is 18.9 ± 0.2 nm. The obtained research results enabled us to develop a chemical model of crystallization of TiC_xN_y–Ni core–shell structures, which is implemented in a hardening chamber at a crystallization rate of 10⁵ °С/s. To fabricate the model, we used the reference data on the boiling and crystallization temperatures of the elements and compounds being a part of highly dispersed compositions and recorded by X-ray diffraction, as well as the ΔG(t) dependences for TiC and TiN.

One of the main problems in the production of bimetals is associated with the difference in the physico-mechanical and structural properties of the materials being joined. Both solid-phase and liquid-phase methods are used to obtain bimetals. The main technological task is to create conditions for the formation of a transition zone between the working layer and adhesively bound substrate. We analyzed the known methods for producing compact and powder bimetals (insert molding, diffusion welding in the solid phase, infiltration, hot isostatic pressing, etc.). The bonding strength of bimetal layers is evaluated according to the results of mecha­nical shear or pull tests; however, such an assessment does not enable to determine if the product can be operated in the mode of frequent thermal cycles. The above method, which involves joint hot repressing of previously separately cold-pressed and sintered blanks of the working layer and substrates, is promising in terms of improving the mechanical and tribotechnical properties, reducing the risk of structural degradation of particles of hardening additives, as well as enhancing the quality of the connection of steel–bronze bimetal layers. In this case, the working layer is heated through heat transfer from the side of the substrate warmed up to a higher temperature. We studied the impact of technological conditions for obtaining hot-forged powder steel–bronze bimetal on the structure, features of thermal fatigue failure and tribological properties and presented the research results. For structural analy­sis, thermal fatigue and tribotechnical tests, the bimetal samples with vertical and horizontal arrangement of layers were obtained. The atomized iron powder PZhRV 3.200.28 was used as a base for fabricating the substrate from PK40 steel. Graphite powder GK-3 (GOST 4404-78) was used as a carbonaceous additive. The working layer was fabricated from BrO10 bronze powder obtained by atomizing. To improve the tribotechnical characteristics of the working layer, bronze powder was mixed with superfine grinding micropowder F1000 of black silicon carbide 53S. The quality of bonding of bimetal layers was assessed based on the thermal shock test results. Tribotechnical tests were carried out in the dry friction mode according to the “shaft–block” scheme. We proposed the technique for producing hot-forged powder bimetal “PK40 steel–BrO10 bronze”, which includes the following independent procedures: cold pressing of the substrate and working layer blanks, their sintering in a reducing environment, pre-deformation heating of the substrate and working layer at temperatures that ensure their satisfactory formability, assembly of heated substrate and working layer blanks in the mold and subsequent joint hot repressing. The resulting bimetal is characterized by increased values of thermal fatigue and wear resistance in comparison with the control samples manufactured using the traditional technology of hot repressing of the cold-pressed bimetallic blank.

Several WC–Co hardmetals with varying WC grain size distributions were analyzed to measure the mean grain size using the linear intercept (L) and planimetric (d_J) methods. Additional measurements included the equivalent diameter (d_eq) and mean chords (d_ch) for all grains, and separately, for grains intersected by the line. The findings show that mean sizes and size distributions of grains intersected by the line differ from those of all grains. This discrepancy is attributed to the linear intercept method’s rule for drawing secants, leading to “shadowing” where finer grains are obscured by coarser ones. The relationship between the mean sizes of all grains and those intersected by the line can be quantified using the “shadow” function S, which depends on the coefficient of variation (c_v) of the WC grain size distribution, as d^a/d^l = 1 – S. Experimental data illustrate that the mean equivalent diameter d_eq correlates with the linear intercept method L through equation d_eq/L = 1.4(1 – S), and the relationship between the mean grain size d_J and L are described by the equation d_J/L = 1.4(1 – S)\(\sqrt {1 + c_{\rm{v}}^2} \). The analysis of grain distributions by the equivalent diameters and mean chords showed that they equally describe the alloy grain size distribution. The length distribution of random chords obtained using the linear intercept method differs from the alloy grain size distribution due to the shadow effect, and also because the length distribution of random chords is always broader than the mean grain chord distribution. It is demonstrated that the length distribution of random chords is a convolution of the grain size distribution function and a function related to the grain shape.

In this research, we combined mechanical activation (MA), self-propagating high-temperature synthesis (SHS), and spark plasma sintering (SPS) methods to obtain a dense high-entropy (Hf,Ta,Nb)(C,N) carbonitride and studied its properties. To implement the SHS process, a mixture of initial metals and carbon was subjected to pre-treatment in a planetary mill in the low-energy mode, in which the jar rotation speed reached 350 rpm. We studied the evolution of microstructure and phase composition during the MA process. It has been established that after 60 min of treatment, Hf/Ta/Nb/C layered composite particles consisting of Hf, Ta, Nb and C submicron layers, with an average size of about 15 μm, were formed. However, according to the X-ray diffraction analysis, the components in the jar did not interact. SHS of Hf/Ta/Nb/C reactive mixtures was performed in a nitrogen atmosphere (P = 0.8 MPa); after synthesis, two isomorphic (Hf,Ta,Nb)(C,N) phases of the Fm-3m (225) space group with lattice parameters of a = 0.4476 nm (71 wt. %) and a = 0.4469 nm (22 wt. %) were revealed in the powder. After SHS, the average size of agglomerates was 10 μm and their morphology resembled that of composite particles after MA. The agglomerates formed during SHS consisted of pores and round-shaped particles ranging in size from 0.5 to 2 μm, which was caused by the melting of metal components in the combustion zone and rapid crystallization of product grains from the melt, followed by subsequent recrystallization. Spark plasma sintering at a temperature of 2000 °C, a pressure of 50 MPa and a holding time of 20 min enabled to obtain a single-phase high-entropy (Hf_0.33Ta_0.33Nb_0.33)C_0.5N_0.3 material with a lattice parameter of 0.4482 nm characterized by a high relative density of 98 %, a hardness of 21.5 ± 0.4 GPa, a Young’s modulus of 458 ± 10 GPa, and a fracture toughness value of 3.7 ± 0.3 MPa∙m^1/2.

A new physical and mathematical model of silicon vapor transport under medium vacuum conditions has been developed, which makes it possible to explain the anomalously intense mass transfer of silicon during high-temperature silicification of a porous carbon material. A formula has been derived showing how the product must be supercooled in order for the condensation process to occur in its pores. The resulting modified diffusion equation makes it possible to determine quantitatively the flow of gaseous silicon into the sample, which is highly demanded in the implementation of the porous fiber carbidization technology and the subsequent complete saturation of the product pores with unreacted silicon. We introduce and quantify a new parameter, showing the contribution of convective transport to the overall mass transfer of silicon through an external gas medium, the role of which is played by argon. An exact analytical solution of the equation for silicon transfer in a one-dimensional formulation has been found for a layer of porous medium with a flat surface. The solution has the form of a logarithmic profile and allows us to calculate the flow of gaseous silicon at the entrance to the product. The proposed approach is demonstrated on the example of two-dimensional calculations performed by the finite diffe­rence method, however, the proposed model is easily generalized to the case of three-dimensional calculations with complex geometry, which always has to be dealt with in a real technological process. Calculations in a two-dimensional formulation have performed for two model systems: when the melt mirror and the product are parallel or perpendicular to each other. The dynamics of silicon vapor propagation in the retort has been studied. It is shown that in the conditions under consideration, gaseous silicon, after the onset of vaporization, fills the entire space of the retort in a characteristic time of less than 1 s.

Additive technologies, in particular selective laser melting (SLM), enable to manufacture the products with complex geo­metries. The SLM technique can help to effectively expand the titanium nickelide scope of application. However, SLM is a complex process – numerous factors significantly affect the characteristics of the resulting alloy. When the SLM technique is used, as the material is subject to laser processing, the content of nickel in the alloy drops due to evaporation, which can lead to changes in the tempe­ratures of martensitic transformations. This impact on the resulting alloy characteristics can be regulated by changing the para­meters of the SLM process. The objective of our research was to develop the processing methods for manufacturing samples from two commercial TiNi alloy powders using the SLM technique and to analyze the factors causing defects in the obtained samples. At the same time, processing methods with low values of volumetric energy density were used to reduce possible evaporation of nickel during printing. The initial powders were examined for the presence of impurities or other factors affecting the quality of the manufactured samples. The processing method A4 that we have developed for powder 1 enables to obtain a defect-free sample with the density of 6.45 g/cm³. It was found that none of the processing methods used enabled to obtain a defect-free sample from powder 2 due to presence of a large amount of oxygen impurities, including in particular Ti₄Ni₂O_х secondary phase, which leads to embrittlement and destruction of the samples. Therefore, high content of oxygen in the initial powders has a negative impact on the quality of the samples manufactured using the SLM technique.

The paper describes experiments on selective laser sintering (SLS) of a high-temperature ceramic material – silicon carbide powder F320 – using the MeltMaster3D-160 SLS unit equipped with a fiber ytterbium laser with a peak power of 200 W. We investigated the sintering mechanism and the impact of technological parameters on the microstructure, phase composition, and density of the resulting 3D cubic samples. The technological properties of the initial powder were also investigated, including morphology, granulometric composition, bulk density, and flow rate. The powder morphology mainly consists of acicular particles with an aspect ratio of 1:5. Granulometric analysis revealed an average particle size of 48 μm. Measurements indicated that the bulk density reached 1.11 ± 0.01 g/cm³, approximately 36.6 % of the theoretical density value. The average time of powder outflow from the Hall funnel was 21.0 ± 0.1 s, with 2–3 hits on the funnel during the measurement process. Experimental cubic samples of 10×10 mm were manufactured using 75 technological modes. Silicon carbide powder particles sinter due to the thermal effect of laser radiation and the release of SiC microparticles on the surface of the powder particles, with silicon (average size less than 1 μm) prevailing in the composition, followed by mutual bonding of neighboring powder particles in the sintering region. X-ray phase analysis demonstrated that due to the laser radiation, the resulting 3D samples contain the following phases: SiC (6H), Si, and C. It was revealed that a scanning step larger than the actual spot diameter (spot diameter + thermal influence zone), 60–70 μm in size, causes the formation of unsintered areas between sintering tracks. The key parameters affecting the density index of the obtained samples are layer height, energy density, and scanning step. The best density index for the obtained samples is 86.7 % relative to the absolute density of the material (3.21 g/cm³). Further research will be devoted to the development of techniques for post-processing the resulting porous samples-blanks to obtain a density close to 100 %.