Rolling bearing rings offer great opportunities for expanding the powder metallurgy production. At present, these opportunities are not fully realized. Hot forging of porous preforms makes it possible to obtain high-density materials for the manufacture of heavy-duty products, in particular rolling bearing rings. The problem of hot-forged bearing ring manufacturing is associated with a large amount of impurities in initial powders, as well as residual one-side open pores and microcracks in the surface layer of parts caused by cooling down of heated porous blanks in such process operations as hot repressing. The paper considers a potential improvement of mechanical properties and  rolling contact endurance of hot-deformed steels with eutectoid composition obtained on the basis of chrome-molybdenum  iron  powder, as well  as unalloyed  iron  powders with  various  impurity  contents due to  microalloying  by sodium. Sodium was  doped as bicarbonate. The  method proposed  previously for producing high-density iron-based chromium-bearing powder material was used in order to reduce the probability of heated porous preform oxidation during hot forging (HF). The method involves obtaining cold-pressed blanks with a porosity of 10–12 % with their sintering in a vacuum furnace and  subsequent HF. 10×10×55 mm prismatic samples were obtained for mechanical test and  structural analysis. Rolling contact endurance was studied using ∅ 26×6 mm cylindrical samples. The tests were carried out by running the flat surfaces of cylindrical samples with balls. Doping Na microadditives can  significantly increase the rolling contact endurance of powder steels compared to unalloyed samples, as well as with respect to check test pieces made of ShKh15 heat-treated steel due to a decrease in austenite grain size, an increase in the quality of interparticle jointing and  a decrease in surface porosity. Carbonaceous powder steels containing the optimum amount of sodium microadditive (0.2  wt.%)  can  be used to  manufacture structural products operating under contact loads.

It is known  that  materials based on MAX phases have great potential for aerospace, automotive and  industrial applications due to a unique combination of features offered by both  metals and  ceramics with high mechanical, chemical, thermal and  electrical properties. This paper provides the results obtained by the SHS metallurgy of Cr–Al–C materials with different ratios between the MAX-Cr₂AlC phase, carbides and  chromium aluminides. Experiments were carried out in a 3-liter SHS reactor at an initial pressure of inert gas (Ar) of 5 MPa.  The synthesis process was  carried out based on coupled chemical reactions: weakly exothermic (heat acceptor) –  Cr₂O₃/3Al/C and  strongly exothermic (heat donor) –  3CaO₂/2Al. The obtained experimental results have a  good correlation with previously performed thermodynamic calculations. It is shown that varying the composition of the initial mixtures can significantly influence the calculated and  experimental synthesis parameters as well as the phase composition and  microstructure of final products. The paper establishes optimal conditions for material synthesis providing a maximum output of the Cr₂AlC MAX phase in the  ingot  composition. A determining factor influencing the  Cr₂AlC content in the final product is the time of liquid phase presence under synthesis conditions. It is shown that  the maximum content of the Cr2AlC MAX phase and  the target product yield is achieved at the highly exothermic additive (3CaO₂/2Al) content of 30 % in the initial mixture.

The paper investigates the possibility of carrying out  SHS  for the Ti (81.5 wt.%)  + B (18.5 wt.%)  composition in the air followed by pressing combustion products in an open steel die with walls limiting their radial flow under tough heat dissipation conditions without the use of an intermediate loose medium of the heat insulator. Modes of reaction powder mixture preparation for synthesis were optimized. Such process characteristics as bulk density, compaction, elastic aftereffect were determined for initial powders and reaction mixtures, and the strength of compactions was estimated. It is shown that there is a relationship between the strength of charge compacts, combustion rate and  changes in their volume after combustion in the air under intensive gas liberation during combustion. The optimal charge compact density was found equal to 0.75  corresponding to the maximum combustion rate without charge emissions with a minimum change in volume. As a result of the optimization, the possibility of effective and  safe conduct synthesis process without the use of an intermediate loose medium of the heat insulator is shown. Hard-alloy plates with a diameter of 60 mm and  a thickness of 11 mm were obtained in the open steel die under SHS compaction conditions. The structure of the resulting hard alloy is unique with a porosity of less than  0.5  %. It consists of titanium diboride (~60  wt.%)  and  titanium-based binder phase (~ 40 wt.%).  Such a structure obtained as a result of accelerated cooling can  be defined as nonequilibrium, since the main phase for the studied composition should be titanium monoboride (TiB) in accordance with the Ti–B state diagram. The microhardness of the fabricated hard alloy is HV = 18000 MPa.

The paper presents the  results of obtaining and  studying the  structure and  properties of cermets based on powders of aluminum oxide and  nickel-aluminum alloy doped with 0.1  wt.% of aluminum-magnesium spinel nanoparticles sintered by the electrospark method on the FCT-HP D 25 unit in argon at t = 1470°C for 30 min. The results of the NiAl–65Al₂O₃ charge TG and  DSC analysis at up to 1300°C are presented. It is found that MgAl₂O₄ spinel in the form of individual nanoparticles (60 nm) or aggregates (less than 700  nm) are present along the grain boundaries of the composite. Internal friction studies at t = 20÷900°C and  high-temperature X-ray phase analysis at t = 700,  800  and  900°C were carried out to describe strength properties degradation mechanisms of the developed materials. The effect of nanoparticles on the internal friction of the composite within Δt = 20÷900°C in the NiAl–65Al₂O₃–0.1MgAl₂O₄ system is shown. Potential mechanisms for cermet strength properties degradation with increasing temperature are discussed. It is suggested that the appearance of extrema on internal friction curves at high temperatures can be caused by shifted phase boundaries of intermetallic compounds and  the oxide component due to different coefficients of thermal expansion (CTE).

A positive effect of doping with spinel nanoparticles on the short-term heat resistance of cermets at t = 750°C is found. The study of short-term heat resistance at t = 750°C showed that  the sample with nanoparticles is more stable than  the unmodified sample, which can be associated with the influence of interfacial hardening zones formed around nanoparticles according to the Obraztsov– Lurie–Belov theory and  a number of studies carried out on metal matrices.

The paper presents the results of studies into the possibility of obtaining Pr₂Fe₁₄B/α-Fe composites by Pr–Fe–B alloy oxidation in a fluidized bed jet mill. It is shown that  Pr₂Fe₁₄B/α-Fe composites with high magnetic characteristics can  be obtained using the standard powder metallurgy technology supplemented by Pr–Fe–B alloy oxidation in a fluidized bed jet mill for rare earth hard magnetic materials. It is found that there is an increase in residual induction (B_r) with a slight drop in the coercive force ( jH_c) during the fine powder production according to the proposed technology in argon containing up to 0.2 vol.% of oxygen. This effect causes the  maximum  energy product (BH)max to  increase  by 5 %.  With  further increase  in  the oxygen concentration,  the Pr_xFe, high-praseodymium phase almost completely oxidizes. This leads to a sharp drop in the coercive force and, as a consequence, to a drop in (BH)_max. α-Fe particles resulting from magnetic material oxidation form at the boundaries between the Pr₂Fe₁₄B phase grains. Maximum magnetic characteristics are achieved when α-Fe particles are separated from the main magnetic phase grains by thin layers of non-magnetic phases. This allows maintaining a high  coercive force jH_c  for sintered hard magnetic material samples. The optimal thickness of α-Fe layers is 0.2–0.3 μm. α-Fe layers were significantly thicker (0.8 to 1.1 μm) for samples obtained at an oxygen content of 0.3 vol.%. As a result, the coercive force of samples reduced by almost 10 %, while other magnetic parameters (B_r , (BH)_max)  decreased by 3–7 %. Therefore, it is possible to change the thickness of the α-Fe phase layer formed in the Pr₂Fe₁₄B/α-Fe composite and  control its magnetic parameters by adjusting the oxygen content in the jet mill medium.

The paper justifies the significance and  effectiveness of silicate-containing inorganic coating usage as an electric insulator in the production of soft magnetic composite materials (SMCM) from iron powders. The study demonstrates the effect of sodium silicate (Na₂O–SiO₂) concentration in the water solution on the kinetics of dielectric coating formation on different iron powder grades, as well as on  their weight gain, average coating thickness, as well as physical and  process characteristics. It is experimentally established that  the influence of iron powder particle morphology and  surface tension coefficient at solid-liquid interface on the coating thickness can be assessed indirectly by the wettability indicators, in particular, by the contact angle. The features of SMCM interlayer boundary structure formation are described. Elemental mapping using the energy dispersive X-ray spectrometer shows that after sample pressing at 600 MPa and their subsequent heating within 400–600°C, the coating thickness changes and silicon is partially redistributed in the dielectric layer. This is determined by the fact that silicon featuring higher oxophilicity than  iron actively reacts with oxygen adsorbed on the iron particle surface and/or reduces iron oxides forming SiO₂ in the form of a dense film, which on the one hand protects iron particles from  oxidation, and  on the other hand forms a dielectric layer in the zone of iron particle contact that  affects specific magnetic losses. It is determined that  the distinctive feature of coated iron powder compaction is the structural deformation predominance during pressing since the coating reduces the internal friction coefficient. It is shown that according to its magnetic characteristics, the developed SMCM meets essential contemporary requirements for soft magnetic composite materials.

The study covers specific features of morphological and  structural characteristics exhibited by nanopowder particles obtained by  grinding  a  massive  natural  diamond  and  the method of detonation  synthesis.  High-resolution  transmission  and  scanning electron microscopy, small-angle X-ray scattering demonstrated that natural diamond nanopowder particles obtained by grinding have a wider range of sizes and  a plated appearance, unlike detonation synthesis nanopowders consisting of similar in size and isometric particles. X-ray diffraction analysis and  Raman spectroscopy used in addition to the methods mentioned above showed that  the structure of nanodiamond particles obtained from  natural diamond is similar to the structure of a detonation synthesis nanodiamond. Each  particle of natural nanopowder, as well as detonation synthesis nanodiamond, consists of a diamond core with a crystal lattice related to the cubic system and  a shell containing mainly non-diamond carbon forms with sp² hybridization having a  complex structure.  The average particle size of nanopowders obtained from  natural diamond and  using detonation synthesis studied by three methods including BET showed results that are in satisfactory agreement with each other. The average nanoparticle size is about 24 nm for natural diamond powder and close to 5.6 nm for UDA-S-GO detonation synthesis nanodiamonds produced by the Federal Research and Production Center «Altai». An insignificant increase in the interatomic distances in diamond nanocrystals compared with a massive diamond crystal was shown experimentally. The study and  analysis of a numerous images of natural and  detonation synthesis diamond nanocrystals obtained by high-resolution transmission electron microscopy made it possible to establish that  the most frequent defects in nanodiamonds are dislocations and  point defects.

Comparative studies of the structural characteristics and  functional properties of Ti–Al–Mo–N and  Ti–Al–Mo–Ni–N coatings obtained by the arc-PVD method were carried out  in order to study the effect of nanostructuring nickel additive. The coatings featured by  multilayered architecture  with alternating layers of  titanium and  molybdenum nitrides. Molybdenum and  nickel concentrations were about 22 at.%  and  7 at.%, respectively, which corresponds to optimal quantities for the best strength and tribological properties. It was shown that  nickel introduction reduces the coating modulation period from  60  to  30  nm  with a simultaneous  increase  in  hardness from  37  to  45  GPa.  At the same time,  an  increase  in  the tensile  strength of coatings  was noted, which was judged by the relative plastic deformation behavior as well as H/E, H ³/E ²  parameters. Ductile nickel added into the solid nitride coating structure led to a decrease in the level of compressive macrostresses in the material from –2.25 to –0.58 GPa,  without, however, any decrease in hardness and  fracture toughness that  was shown by scratch tests. It is concluded that  the factor determining mechanical characteristics of the coating is not  the macrostressed state, but  the refinement of the coating material grain structure. Nickel positively affected the coating heat resistance successfully protecting the substrate material from oxidation at temperatures up to 700°C, which may be associated with the likelihood of the formation of NiMoO₄ and NiTiO₃ nickel-containing oxides on the surface. However, their formation, fracture, and  action as abrasive particles can  cause a change in the friction wear mechanism at high temperatures.