Design of ceramics with predetermined microstructure is based on the arrangement of concordant structure transformations under sintering of selected phase components, whose evolution determines the formation of required microstructure elements, their crystal morphology, scale, content, and distribution throughout the volume. Such elements may include grains, intergrain and interphase boundaries, elements of substructure responsible for the appearance of intragrain boundaries,such as dislocation, twinning, domain, and interphase ones, and pores of different types. Knowledge of these mechanisms is the base for design of novel materials an dimprovement of the currentones. The grain structure is a basic material structure component. Based on our research (using TEM with microdiffraction and SEM with microanalysis) and literature data, general regularities of grain structure formation in ceramics are considered in the course of primary (PR) and collective (CR) recrystallization and during formation of composites under sintering. It’s worth noting that recrystallization in ceramics was first studied by G.V. Samsonov at our Institute. PR in ceramics can occur under different conditions of loading such as free sintering, hot pressing including that under highpressure, uniaxial compression, rolling, friction, etc. The structural mechanisms of the PR evolution in ceramics are similartometals. The formation of grain structure in composites is determined by structure transformations due to the contact interaction of phase components; transformations in the grain volume of initial phases (plastic fragmentation, polymorphic transformations, decomposition of solid solutions, twinning, domainization, etc.); transformations in grain boundaries (phase transitions, boundary faceting, etc.). All of them lead to refining grain structure due to the formation of new grains and saturation of the initial ones with internal boundaries resulting from substructure formation [1].

The deformed biomedical Ti-(18-20)Nb-(3-4)Zr-(1-1.2)Si (% wt.) alloys are studied. Their rolling is carried out at 950 degrees & Scy; by means of the air- and water-cooling; the quenching in water and oil with heating up to 1050 degrees & Scy; is also used. As established with the x-ray phase analysis, the hot deformation of Ti-(18-20)Nb-(3-4)Zr-(1-1.2)Si alloys contributes to the 6- solid-solution heterogeneity into 6 1 phase based on Ti-Nb and 6 2 phase based on Zr-Ti, as a result of which a final dispersed nonequilibrium ( alpha '' + alpha ' ) structure is formed after cooling, that reflects the ( 6 1 + 6 2 ) microstructure formed due to the previous decomposition. After deformation with air cooling, the experimental alloys contain the largest amount of alpha ' phase and have high strength and low plasticity. As shown, a rising of the cooling rate and temperature during quenching leads to the predominance of the orthorhombic alpha '' phase, while the strength of the alloys decreases with a significant increase in plasticity. In the process of deformation and heat treatment, densely and uniformly distributed disperse silicides are also released in the structure, which contribute to the strengthening. For Ti-(18-20)Nb-(3-4)Zr-(1-1.2)Si alloys, the temperature range & Tcy; = 1040 +/- 20 degrees & Scy; is established, the quenching from which allows to obtain high mechanical properties: cs & vcy; = 1100-1150 & Mcy;P & acy;, cs 0.02 = 800- 850 & Mcy;P & acy;, 8 = 11-11.5%. By deformation and quenching of the experimental alloys, a composite material with alloyed soft matrix strengthened by the uniformly distributed dispersed hard particles of silicides is fabricated.

In the present work, we report on structure formation of ultradispersed diamond through detonation synthesis. In particular, based on the present data, we can state that ultradispersed diamond of detonation (UDD) synthesis is characterized by a rail substructure formation, which is typical for diamonds of dynamic and static synthesis formed from graphite by the martensitic mechanism. The formation of UDD is characterized by a two-stage process: the first stage is the formation of graphite from detonation products, and the second stage is the transformation of graphite into diamond by the martensitic mechanism. A microlamellar substructure in the rails of diamonds formed from the original graphite is due to the presence of basic packing defects that is characteristic for covalent crystals with a wurtzite lattice deformed at high pressures and temperatures typical for lonsdaleite. The presence of lonsdaleite in UDD also indicates its formation in the process of synthesis of diamond from graphite through the martensitic transformation.

The heat-resistant Ti–Al–Zr–Si alloys (base Ti–(6–7)Al–(2–3) Zr–(1–1.5)Si and additionally alloyed Ti–(6–7)Al–(3–5)Zr–(1–1.5)Si–(2–4)Sn), obtained by electron beam smelting were studied. Deformation was carried out in the β- or upper part of the (α+β)-area by means of forging and rolling into a strip. The base alloy was subjected to rolling in the upper part of the α+β-area, and the fine-grained uniform structure with a grain size of 10–20 μm was obtained. Internal stresses and defective substructure of the deformed alloy intensify the decomposition of the solid solution and promote the formation of evenly distributed dispersed silicides, which allows obtaining high strength and heat resistance characteristics. Tensile tests at 20; 650 and 700°C of the Ti–(6–7)Al–(2–3)Zr–(1–1.5)Si alloy samples after deformation and annealing also showed a rather high level of the tensile strength and yield strength. After 20 h exposure at the operating temperature of 700°C, the structure becomes more equilibrium, due to which the strength of the deformed alloy decreases, and the relative elongation increases. Additional alloying of the base alloy with zirconium and tin slightly increases plasticity and decreases heat-resistant properties.

This work is focused on the effects of the laser heat treatment (LHT) followed by ultrasonic impact treatment (UIT) on the surface texture and mechanical properties of the hardened surface layers of the AISI O2 tool steel. The scan-assisted laser surface transformation hardening process was performed at a strategy of constant heating temperature using a fiber laser and galvanometer scanner. The subsequent severe plastic deformation of the laser-hardened steel parts was conducted using a multi-pin ultrasonic tool. Results showed that the multi-pin UIT treatment of the LHT-processed tool steel parts reduced the average surface roughness from ~ 0.6 to ~ 0.35 µm and increased the average sub-surface microhardness by ~ 15%. Additionally, the multi-pin UIT provided the nanograin structure in the near-surface layer hardened by the scan-based LHT. AISI O2 tool steel parts were selectively processed by the laser surface transformation hardening process followed by the multi-pin ultrasonic impact peening process. The surface texture, roughness, waviness, microhardness, hardening depth, residual macro-stresses, and microstructural observations obtained by XRD, SEM, TEM, and SAED were studied after the combined laser-ultrasonic hardening and finishing process.

The influence of structural-phase changes during hot isostatic pressing (HIP) below the temperature of alpha -> fl transformation on the mechanism of porosity healing of the powder near-beta alloy Ti-5Mo-5 V-5Al-3Cr (Ti -5553, in wt%) is studied, as it has been also done by us earlier for the powder near-beta alloy Ti-10-2-3. Both alloys have nearly the same beta phase fraction, but significantly differ in the stacking fault energy (SFE): in the Ti-5553 alloy, it is approximately an order of magnitude lower than in the Ti-10-2-3 alloy. This feature has a significant effect on the structural phase state of the alloys after HIP under completely identical processing conditions. In the Ti-5553 powder alloy, numerous twins and helical dislocations form at all processing stages (synthesis, HIP, active deformation after HIP), which actively interact with each other. The interaction between them leads to material reinforcement and, as a consequence, to hardening. Healing of pores under HIP of the Ti -5553 powder alloy occurs in two stages. The first one is the spontaneous transformation of low-mobility screw dislocations into helical dislocations under the action of high chemical stresses formed due to supersaturated vacancies. The second stage is the absorption of supersaturated vacancies by numerous edge-oriented jogs in the helical dislocations. Supersaturation is caused by the diffusion resorption of pores. The low SFE and the pecu-liarities of the chemical interaction with supersaturated vacancies lead to the formation of structural defects hitherto unobserved in this alloy - densely coiled helical dislocations with wide spiral stacking faults. The plasticity of the alloy after HIP increased 4.3 times compared to the state after sintering. However, pore healing in the Ti-5553 powder alloy under HIP below the beta-transformation is less effective compared to the Ti-10-2-3 powder alloy. The reason is that the number of vacancies that can be absorbed by jogs at helical dislocations in the Ti-5553 alloy is not as high as the number of vacancies that can be absorbed by interphase and grain boundaries, as it occurs in the Ti-10-2-3 alloy.

In this study, hypoeutectic Al–Cu/C composite powder was produced via mechanical mixing (for 20 min) and mechanical alloying for 1 and 8 h. The milled for 8 h powder then was annealed at the temperatures below the sintering point (400 and 500 °C) for an hour. The samples were collected after each stage of treatment and studied using by X-ray diffraction (XRD), differential scanning calorimetry (DSC), Raman spectroscopy, nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). The results showed the structural disorder of graphite and the kinetics of aluminum carbide (Al4C3) formation. Furthermore, the average crystallite sizes in the direction of the graphite plane (La) were also estimated. Transmission electron microscopy (TEM) additionally confirmed presence of the metastable disordered Al4Cu9 phase in the milled for 8 h powder and the carbide after its annealing at the temperatures of 400 °C and above. The effect of defects, which become the most favorable reaction sites between aluminum and carbon, was discussed.

The work compares ceramic materials based on ZrO 2 co-stabilized with 8 mol. % of CeO 2 and 2 mol. % of Y 2O3 (8Ce2YSZ) and stabilized with 3 or 8 mol. % of Y 2O3 (3YSZ and 8YSZ). Both hydrothermal and co-precipitation approaches were used for powder preparation. The formation of a tetragonal structure with 6–8 % residual porosity and enhanced biaxial bending strength was observed for the 8Ce2YSZ samples. The 8YSZ and 3YSZ samples have cubic and tetragonal/monoclinic phases, respectively, with about 1% porosity and smaller strength values. The specific electrical conductivity of 8Ce2YSZ and 8YSZ is 1.1·10-3, 4·10-3, 1.2· 10 −2 S/cm and 5.2 · 10 −3 , 2.7· 10 −2 , 9.3· 10 −2 S/cm at 600, 700, 800 °C, respectively. The 8Ce2YSZ material developed is promising to be used in SOFC carrier anode layer due to higher mechanical strength comparing with 8YSZ. Moreover, the presence of cerium may improve the efficiency of anode electrode due to additional electronic conductivity, and better branching of the anode reaction zone.

We study the biomedical Ti-18Nb-4Zr-x Si cast alloys with a silicon content of 0.5-1.5 wt.%. Quenching in water was carried out within the temperature range 900-1200 degrees? with durations of holding equal to 5 min and 1 h. It is discovered that the procedure of heating of these alloys to the temperatures of quenching leads to the decay of nonequilibrium phases, and the silicon content is redistributed between the phases in a solid solution and silicides. Since almost all silicon is bound with zirconium and titanium and form silicides, the hardness of the Ti-18Nb-4Zr-x Si alloys mainly depends on the amount of silicides and constitutes 26-28 HRC. Moreover, its maximum values are reached for the alloys with eutectoid compositions containing 0.8-1.2 wt.% Si characterized by the most intense release of finely divided silicides. The increase in the silicon content of the hypereutectoid alloys leads to an increase in the sizes of silicides, as well as to the formation of larger amounts of the beta-phase in the as-cast Ti-18Nb-4Zr-x Si alloys, and as a result, their hardness noticeably decreases. For low quenching temperatures (within the range 900-1000 degrees C), the complete eutectoid destruction accompanied by the formation of relatively large stable (Ti, Zr)3Si silicides leads to a decrease in hardness < 25 HRC. In the course of quenching of the as-cast Ti-18Nb-4Zr-x Si alloys at temperatures >= 1100 degrees C, we observe the formation of more finely divided silicides, which increases the level of hardness of the eutectoid alloys up to 38-39 HRC. The observed changes in the parameters of the alpha ''-phase demonstrate that, as a result of partial dissolution of silicides in the course of quenching at 1200 degrees C, silicon passes into a solid solution and the amount of large silicides on the grain boundaries increases. Therefore, the level of hardness of the analyzed quenched alloys decreases.

Solid oxide fuel cells (SOFC) are among the most promising technologies for the electricity generation due to their high efficiency, reliability, flexibility in fuel selection, absence of valuable platinum group metal catalysts, safety and environmental friendliness.Typically, the SOFC is built on the basis of its anode, which is actually also its carrier. This is due to the researchers wish to minimize the ohmic resistance of the electrolyte layer via its thinning that is extremely critical for reducing SOFC operating temperature. In this regard, the anode must be strong enough both to make it easier to handle when making the whole cell and to ensure its stable operation. In addition to the carrier function, the anode shall provide sites for reacting gaseous fuel with oxygen ions, which are delivered through the electrolyte, and supplying the fuel gas components to the reaction sites and removing the fuel oxidation reaction products to the outside.The work deals with the comparative study of ceramic materials based on ZrO2, co-stabilized with CeO2 and Y2O3, and stabilized with Y2O3to be used in producing the SOFC anode, and for further structural optimization for future SOFCs.8Ce2YSZ ceramic samples made by hydrothermal synthesis (with two different modes of drying precipitation) have tetragonal phase and 6—8% residual porosity. The 8Ce2YSZ samples, showed the biaxial bending strength — 542 MPa and 486 MPa, respectively. The 8YSZ and 3YSZ samples have cubic phase with a strength of 181 MPa and tetragonal phase with a strength of 577 MPa, respectively at 1% porosity.The specific electrical conductivity of 8Ce2YSZ and 8YSZ is 1,1•10-3, 4•10-3 S/cm, 1,2•10-2 S/cm and 5,2•10-3, 2,7•10-2 S/cm, 9,3•10-2 S/cm at 600, 700, 800 °C, respectively. Keywords: solid oxide fuel cell, electrolyte, anode, zirconium dioxide, mechanical strength, ionic conductivity.

The paper presented some results from the electron microscopic study of structure formation processes in boron carboxynitride (BNCO) during its synthesis on the basis of initial boron oxide and melamine in the form of a powder and a coating on single-crystal diamond particles. Structural studies were performed by transmission electron microscopy (TEM) including high-resolution TEM in combination with elemental microanalysis. Turbostratic BNCO with a different degree of ordering was established to be a major component during the synthesis of a single-phase powder in the temperature region T = 700–1200°C. At a temperature of 1200°C, the formation of an ordered phase occurred in the particles together with inclusions shaped as nanotubes, onions, and prisms with a size of up to 100 nm. BNCO precipitations on diamond particles were monolithic and have continuous interfaces with diamond. The sintering ( р = 7.7 GPa, Т = 1700°C) of BNCO as a single phase and in composition with diamond (both particles with a coating and in the form of a powder) was accompanied by the formation of the sphalerite phase with a graphite-like residue. The sphalerite phase was a major component of sintered samples only when diamond powders with a grit size of 0.1/0 were used.

Проведено дослідження литих стопів Ti-18Nb-хSi з вмістом кремнію від 0,6 до 1,2% ваг.Вивчали утворення силіцидів за різних умов термообробки (температури і витримки), їхній розподіл, динаміку росту та розчинення, а також вплив на твердість і біологічні властивості.Найбільше виділення силіцидів (Ti, Nb) 3 Si відбувається в результаті евтектоїдного розпаду твердого розчину за 800-900°С.У процесі гартування в інтервалі температур ≤ 1000°С переважно на межі зерен і дефектах структури виділяються силіцидні частинки з розмірами > 0,05 мкм, які не впливають на рух дислокацій у випадку пластичної деформації.Тому за даних температур стопи не зміцнюються, їхня твердість є досить низькою.Витримка призводить до зростання розмірів силіцидів і

Results of an investigation by scanning electron microscopy methods of the microstructure of self-reinforced aluminum nitride obtained on the basis of aluminum nitride powder and containing 3 mass.% oxygen by plasma-chemical synthesis in the temperature range 1700-2000 °C are presented. Initial aluminum nitride was represented by the wurtzite (2H) phase. Samples were obtained by free sintering in a nitrogen atmosphere. It was established that, during sintering of AlN in the indicated temperature range, three microstructural types of the material and six types of interfaces (three types of intergranular and three types of intragranular ones) formed. The features of the microstructure of the materials are fully determined by the development of intergranular crystal-oriented polytype transitions of 2H AlNmultilayer polytypes (MP) in sintering. The sequence of successive structural transformations that determine the development of polytype transitions was established. 1. Formation of initial 2H AlN grains of the solid solution 2H AlN-O. The substitution of nitrogen by oxygen takes place. 2. The development of isomorphous delamination of the solid solution in every grain with the precipitation of an interlayer enriched in oxygen. 3. In interlayers, polytypes consisting of a series of polytypes with different number of layers (MP) form. Such an interlayer has developed base surfaces and propagates from one boundary to another in the grain, which determines the formation of a special structural state of fragments of boundaries, that border interlayers in the direction . 4. The high mobility of the indicated fragments of boundaries determines their break-off from the common boundary and formation of a grain nucleus of anisometric (plate-like) shape. This process begins already at a sintering temperature Tsint. = 1800 °C, and, at Tsint. = 2000 °C, polycrystals practically entirely consist of grains of plate-like shape. In this case, with increase in the sintering temperature, the aspect ratio (the length-to-width ratio) of such grains rises. Keywords: aluminum nitride, polytype transformations, grains, microstructure, boundaries, self-reinforcement.

The efficiency of thermomechanical processing was studied to optimize the mechanical properties of cast ternary and multicomponent hypoeutectic titanium-based alloys with silicide–boride reinforcement, produced by electron-beam crucible-skull melting. All the alloys studied exhibit low plasticity in cast state. High-temperature deformation, such as forging of samples heated to 1050°C in air, can significantly enhance the properties of the alloys: the plasticity of ternary Ti–Si–B alloys increases by four to six times (from 0.5 to 2–3%) and their fracture toughness increases by three times (from 11 to 36 MPa ∙ m0.5). The plasticity of the alloys with Zr, Al, and Sn additions increases by one order of magnitude (to 0.2–0.3%) and their fracture toughness by almost twice. The greatest high-temperature creep-rupture resistance at a fracture toughness of 26 MPa ∙ m0.5 is shown by the Ti80Zr1.2Al5.5Sn2.1Si8.7B2.5 alloy: 1038, 887, and 572 MPa at 600, 700, and 800°C, respectively.

Results of an electron microscopic investigation of particles of lonsdaleite powder with additives of cubic diamond and polycrystalline specimens based on it at Р = 7,7 GPa in the temperature range 1700―1900 °С are presented. Lonsdaleite particles are characterized by a predominantly ternary texture [1120]l of different degree of perfection. Structural mechanisms of transformations in lonsdaleite particles, which cause the formation on nanograined structure in sintering, have been established. The initial stage is the mechanical dispersion of particles and dispersion as a result of plastic faulting deformation, which promotes their fragmentation without breakdown of continuity. The indicated processes lead to the destruction of texture in particles. Beginning from 1700 °С, the lonsdaleitecubic diamond phase transformation with the orientation ratio (111)dII (001)l occurs. It is realized within rods as elements of the substructure of lonsdaleite. At 1900 °С, the size of detected elements of the structure (grains) is 5―15 nm. Beginning from 2000 °С, the self-association of such grains into aggregates with sizes up to 70 nm and the subsequent process of coalescence of grains in aggregates with the formation of the monocrystalline state occur. The next stage of formation of the granular structure is caused by the formation of grain boundaries and development of collective recrystallization. After sintering at Т = 2100 °С, the grain size in specimens does not exceed 100 nm. It has been established that the transformation in lonsdaleite proceeds by structural mechanisms that are characteristic of wurtzite modifications of boron nitride and silicon carbide (strong disordering in the direction of the basal axis, plastic faulting deformation, and formation of multilayer polytypes during the hexagonal-to-cubic phase transformation). Keywords: lonsdaleite, particles, sintering, fragmentation, grains, coalescence.

Variations in the phase composition, specific surface area, and morphology of structural components in the ultrafine powder of composition (wt.%) 70 (90 ZrO 2 (3 Y 2 O 3 , 2 CeO 2 )–10 Al 2 O 3 )–30 CoAl 2 O 4 (70ZA30CoA), produced by hydrothermal synthesis combined with mechanical mixing, were studied in the heat treatment process up to 1300°C. The study employed Xray diffraction, scanning and transmission electron microscopy, petrography, and BET. The formation of CoAl 2 O 4 in the 70ZA30CoA powder in the heat treatment process was accompanied by reversible phase transformations: T-ZrO 2 → M-ZrO 2 → T-ZrO 2 . The M-ZrO 2 content increased from 15% to 46% in the temperature range 850–1000°C and decreased to 13% after heat treatment to 1150°C. The process involved slight coarsening of the primary T-ZrO 2 particles, while the size of the primary M-ZrO 2 particles remained practically unchanged. The phase transformation was due to a decrease in the free energy of the ultrafine 70ZA30CoA powder, representing a thermodynamically nonequilibrium system. The phase composition changed color of the 70ZA30CoA powder in the following sequence: gray → gray blue → dark cyan → bright blue. Morphological analysis of the structural components showed that the CoAl 2 O 4 formation and reversible T-ZrO 2 → M-ZrO 2 phase transformation were accompanied by shape change, loosening, and subsequent sintering of the agglomerates. The chain-like agglomerates of various shapes and sizes indicate that the 70ZA30CoA powder sinters actively at 1300°C. The decrease in the specific surface area from 46 to 1 m 2 /g depending on the heat treatment temperature was determined by the development of three structural transformation processes: formation of CoAl 2 O 4 , phase transition of the ZrO 2 solid solution, and sintering of the 70ZA30CoA powder. The established regularities are of fundamental importance for the microstructural design of ZrO 2 composites such as ZrO 2 –Y 2 O 3 –CeO 2 –Al 2 O 3 –CoO materials of blue and other colors for various applied purposes.

The relation between phase and structural changes and porosity healing that occurred during hot isostatic pressing (HIP) in the near-beta Ti-10V-2Fe-3Al alloy obtained by powder metallurgy was studied. The powders were pressed at room temperature at 750 MPa in air, and then sintered at 1250 degrees C in vacuum. The residual porosity did not exceed 4.1 vol%. After sintering the HIP treatment was carried out in an argon atmosphere without a container. At the optimal HIP regimes (750 degrees C, 200 MPa), at which the porosity was completely healed, the structure transformed into the alpha + beta-lamellar type of basket weaving. The dislocation density after HIP treatment mainly increased in the interphase boundaries due to the action of hydrostatic stresses. Nucleation and growth of the secondary alpha-phase occurs during HIP on the omega-phase particles inside the beta-phase. It is shown that the main mechanism of porosity healing in the Ti-10V-2Fe-3Al alloy during HIP is the diffusion of vacancies along cores of the dislocations accumulated at the interphase boundaries. The plasticity of the alloy after HIP increased 2.5 times compared to the state after sintering. It was found out that the mechanism of tensile deformation after HIP, as well as after sintering, is controlled by the alpha-phase.

In spite of great efforts undertaken to produce and examine the properties of new high-entropy alloys (bulk or film alloys), the available information is still insufficient for creating scientific ideas that would connect the properties and process parameters of these alloys. We studied the dependence of the composition and structure of Co–Cr–Cu–Fe–Ni films deposited by magnetron sputtering on the physical parameter such as energy flux delivered to the growing film surface. This parameter is directly related to process parameters such as magnetron discharge current (Id) and substrate bias voltage (Ub). The films have a nanocrystalline microstructure and crystallize as a two-phase fcc and bcc solid solution with the following lattice parameters: a = 0.363 nm for the fcc phase and a = 0.294 nm for the bcc phase. Ion bombardment of the growing film induced by bias voltage Ub varying from 0 to –300 V in the substrate influences the film structure and composition. Thus, the films deposited at ~300 eV are noticeably depleted of copper, while the composition of the films deposited without ion bombardment is the same as that of the target. Greater energy flux delivered to the growth surface (higher Id and/or Ub in the substrate) increases the growth surface temperature, leading to grain coarsening and film texturing. The bcc phase also substantially decreases in volume, vanishing in the films deposited at Ub = –300 V. The films formed by the bombardment of ions with ≈100 eV energy showed the maximum (~19 GPa) microhardness.

The results are given of the electron-microscopic studies of the initial powders of ultradisperse diamonds with the tBN coating and after sintering of these powders both in the initial state and with coating. The possibility has been found of the interaction of the initial components in the course of sintering to form diamond-like phases.

Проведено дослідження литих загартованих стопів Ti-18Nb-хSi із вмістом кремнію від 0,6 до 1,2% мас.у порівнянні з подвійним стопом Ti-1Si.Вивчався вплив кремнію та температури гартування на їхні структуру та твердість.Показано, що у стопах Ti-18Nb-хSi (х = 0,6-1,2% мас.) при гартуванні, залежності від температури, утворюється мартенсит різної морфології та дисперсности.За даними електронної мікроскопії та мікрорентґеноспектрального аналізу у стопах присутні силіциди (Ti,Nb) 3 Si, кількість і розмір яких також залежать від