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Aluminum nitride (AlN) and boron nitride (BN) are well-known ceramic materials with numerous valuable properties, whereas recently there is a growing field of research on the AlN/BN advanced ceramic materials. Here, we present a study on boron-rich AlN, structural and electronic properties, and structure–property relationship. Several AlxB1−xN solid solutions (x = 1,.875,.75, and.625) have been investigated, and structure optimization has been performed for four different structure types: h-BN, wurtzite, sphalerite, and rock salt. First-principles calculations were performed using hybrid B3LYP functional. New modifications and compounds have been predicted as a function of boron concentration in AlN, and especially, interesting phase transitions were found at extreme pressure conditions. Electronic properties and band structures were computed, and the possibility for bandgap tuning has been discovered. The present study, and especially the structure–property relationship, gives new possibilities for bandgap engineering in boron-rich AlN electroceramic materials. © 2022 The American Ceramic Society.

Synthesizing bulk nanocrystalline materials is challenging since grain growth should be suppressed whereas densification promoted. Here, we demonstrate a novel route to synthesize superhard bulk nanocrystalline cubic boron nitride (cBN), which combines the use of emulsion detonation and high-pressure high-temperature transformation-assisted consolidation. The emulsion detonation process activates BN to possess unique structure and chemistry, i.e. wurtzitic BN nanograins in hexagonal BN matrix with enhanced structural disordering and oxygen impurity, a combination that enhances the nucleation rate of cBN and its densification leading to the formation of bulk nanocrystalline cBN at reduced conditions. The cBN, synthesized at 7.5 GPa and 1800 °C, displayed Vickers hardness values of 50−62 GPa for 5−20 N loads. The findings in the study suggest a feasible solution to synthesize bulk nanocrystalline cBN in a more scalable way, while also providing design insights on how to refine grain growth while enhancing densification to synthesize bulk nanocrystalline materials.

The correlations between structural features, critical current density and pinning landscape of YBa2Cu3O7-δ and MgB2-based materials produced in the forms of bulk melt-textured (MT-YBCO) and polycrystalline (MgB2) blocks and wires with excellent superconducting characteristics were revealed. The impurity oxygen distribution, higher borides inclusions and carbon doping are most important for the critical currents and pinning forces in MgB2, while the twin density and the density of Y211 inclusions are relevant in MT-YBCO.

The correlations between structures and mechanical characteristics of α-AlB12-, AlB12C2-, B4C-based lightweight ceramics and composites synthesized or sintered by hot pressing (at 30 MPa) and SiC-based ceramics obtained by reactive sintering are compared. The effect of C, TiC and SiC additions on the properties of the resultant composites and the particularities of the ceramics destruction under shock loading are discussed. Ballistic tests performed on 10 mm thick plates fabricated from the developed ceramics (2.63 g/cm3 density; 78 wt% B4C and 22 wt% SiC composition according to X-ray diffraction analysis; B3.64CSi0.01 and SiC1.07 stoichiometry according to SEM microprobe X-ray analysis), showed that the material could withstand a 10 m distance shot using a bullet with initial kinetic energy of 3.7 kJ.

The composition of MgB2-based materials (wires, bulks, and thin films) with high critical current densities, jc, prepared at different pressure (0.1 MPa–2 GPa)—temperature (600–1050 °C) conditions was analyzed by the X-ray and JAMP−9500F Auger spectrometer (after removing the oxidized layers at the sample surfaces by Ar ion etching performed directly in the vacuum chamber of a microscope). Similar regularly distributed inhomogeneities connected with Mg, B, and admixture O content variation on the nanolevel were observed in all types of the MgB2-based materials. The correlations between the character of the material inhomogeneities and the attained superconducting characteristics are discussed.

The influence of technological parameters (composition of precursor powders, type of additions, temperature, and pressure) on the superconducting characteristics (transition temperature, critical current density, and critical magnetic fields) of MgB2-based materials (bulk, wires, and thin films) and the correlation with their microstructure were studied. Microstructural observations are in good agreement with ab -initio modeling. The X-ray, Auger spectroscopy, and SEM EDX study show that impurity oxygen and carbon (possibly as dopant) are present in the magnesium diboride structure. The elements are distributed inhomogeneously, thus creating the nanostructure (which can be purposefully changed by manufacturing conditions) responsible for flux pinning and other SC characteristics.

The influence of the structure type on the boron nitride (BN) properties such as excellent thermal and chemical stability and super hardness is well known. The effect of aluminum addition on four different structure types of boron nitride (wurtzite, h-BN, sphalerite, and rock salt) and its electronic properties have been investigated in our study. Here we present an ab initio study of the B1-xAlxN solid solutions for (x ​= ​0; 0.125; 0.25; 0.375 and 0.5), and corresponding structure-property relationship. Novel structures have been discovered in new Al-rich boron nitride compounds and some of them indicate AlN-BN layer separation. Electronic properties have been studied in great detail using hybrid B3LYP approximation. Present results suggest great diversity of the electronic properties generated by adding aluminum to boron nitride and that by using these predicted modifications in various investigated AlN-BN compounds, one could obtain fine-tuning of the band gap in boron nitride electroceramics.

Magnetic nanoparticles (MNP) have attracted considerable interest in many fields of research and applied science due to their impressive properties. In the past, especially biomedical problems have promoted the development of MNPs. For technical applications e.g. wastewater treatment and absorption of electromagnetic waves, the existing synthesis approaches are too expensive and/or the producible quantities are too low. In this work we present a method for simple preparation of size-controlled magnetic iron oxide nanoparticles by electroerosion dispersion (EED) of carbon steel in water. We describe the synthesis method, the laboratory installation and discuss the structural, chemical and electromagnetic properties of the synthetized EED powders as well as their applicability for microwave absorption compared to other available ferrite powders.

У роботі вивчені характеристики структури, твердості, пружності та кавітаційної стійкості матеріалу катодів на основі MAX фази Ti2AlC, виготовлених методом гарячого пресування, а також іонноплазмових покриттів, осаджених з використанням цих катодів на титановий сплав Ti6Al4V. Встановлено, що матеріал катода, який містить 83 ваг. % MAX фази Ti2AlC, характеризується твердістю 10 ГПа, значенням параметра Н/Е 0,04 і низькою кавітаційною стійкістю. Середній кавітаційний знос катоду у 4 рази вище, ніж знос титанового сплаву Ti6Al4V. З'ясовано, що елементний і фазовий склад осаджених покриттів відрізняється від складу катода. Основною фазою в покриттях є нанокристалічний карбід (Тi, Al) C з кубічною структурою типу NaCl. Покриття Ti0,58Al0,17C0,25, осаджене методом іонного розпилення за допомогою дугового джерела газової плазми, характеризується твердістю 21 ГПа. Твердість вакуумно-дугового покриття Ti0,65Al0,07C0,28 ближче до твердості катоду – 13 ГПа, що пов'язано з наявністю в його складі α-Ti. Співвідношення Н/E у покриттів в 1,5 рази вище, ніж у катода, що є передумовою високої кавітаційної стійкості. Середня швидкість кавітаційного зношування вакуумно-дугового покриття Ti0,65Al0,07C0,28 у 1,5 рази нижче, ніж вакуумно-дугового покриття TiN і в 3 рази нижче, ніж сплаву Ti6Al4V без покриття. In this work, the characteristics of the structure, hardness, elasticity, and cavitation resistance of the material of Ti2AlC MAX phase cathodes manufactured by hot pressing, as well as ion-plasma coatings deposited using these cathodes on titanium alloy Ti6Al4V, have been studied. It was found that the cathode material, which contains 83 wt. % MAX phase Ti2AlC, is characterized by a hardness of 10 GPa, a H/E value of 0.04, and low cavitation resistance. The average cavitation wear of the cathode is 4 times higher than that of the titanium alloy Ti6Al4V. It was found that the elemental and phase composition of the obtained coatings differs from the composition of the cathode. The main phase in the coatings is nanocrystalline carbide (Ti, Al) C with a cubic structure of the NaCl type. Ti0.58Al0.17C0.25 coatings deposited by ion sputtering using an arc gas plasma source are characterized by a hardness of 21 GPa. The hardness of vacuum-arc coating Ti0.65Al0.07C0.28 is closer to the hardness of the cathode – 13 GPa, which is due to the presence of α-Ti in its composition. The H/E ratio of the coatings is 1.5 times higher than that of the cathode, which is a prerequisite for high cavitation resistance. The average rate of cavitation wear of vacuum arc coating Ti0.65Al0.07C0.28 is 1.5 times lower than that of the vacuum arc coating TiN and 3 times lower than that of the uncoated Ti6Al4V alloy.

Вивчено процес осадження покриттів шляхом розпилення мішені на основі MAX-фази Ti2AlC з використанням джерела газової плазми. Показано, що MAX-фаза Ti2AlC відноситься до важкорозпилюємих матеріалів. Зі збільшенням енергії розпилення іонів Ar+ з 400 до 1200 еВ коефіцієнт розпилення мішені на основі MAX-фази збільшується з 0,2 до 0,7 атом/іон. Отримані значення в 1,5 рази нижчі за коефіцієнти розпилення мішені з титану. Фазові перетворення відбуваються на поверхні мішені і пов'язані з розпадом MAX-фази та селективним розпиленням більш легких елементів іонами Ar+. Було встановлено, що на склад нанесених покриттів суттєво впливає величина потенціалу зміщення на підкладці. Зі збільшенням потенціалу в діапазоні від 50 до 200 В відносний вміст алюмінію в покриттях різко падає на користь титану від Ti:Al = 3,5:1 до Ti:Al = 48:1. Незалежно від складу, твердий розчин (Ti, Al)C утворюється в покриттях з кубічною кристалічною решіткою типу NaCl, розміром кристалітів 10-15 нм і текстурою осьового типу. MAX-фаза Ti2AlC в покриттях не виявлена. Покриття мають високу твердість і модуль Юнга, які збільшуються зі зниженням концентрації алюмінію в межах 21-30 ГПа та 290-340 ГПа. The process of coating deposition by sputtering a target based on the MAX phase Ti2AlC using a gas plasma source has been studied. It has been shown that the MAX phase of Ti2AlC refers to hard-sputtering materials. With an increase in the sputtering energy of Ar+ ions from 400 to 1200 eV, the sputtering coefficient of the target based on the MAX phase increases from 0.2 to 0.7 atom/ion. The obtained values are 1.5 times lower than the sputtering coefficients of the target from titanium. Phase transformations occur on the target surface and are associated with the decay of the MAX phase and the selective sputtering of lighter elements due to the bombardment by Ar+ ions. It was found that the composition of the deposited coatings is significantly affected by the magnitude of the bias potential on the substrate. With increasing potential in the range from 50 to 200 V, the relative aluminum content in the coatings drops sharply, in favor of titanium from Ti:Al = 3.5:1 to Ti:Al = 48:1. Regardless of the composition, a solid solution (Ti, Al)C is formed in the coatings with a cubic crystal lattice of the NaCl type, a crystallite size of 10-15 nm and an axial type texture. The MAX phase Ti2AlC was not detected in the coatings. Received coatings have high hardness and Young's modulus, which increase with decreasing aluminum concentration in the ranges of 21-30 GPa and 290-340 GPa.

The superconducting transition temperature of 140 nm ± 10 nm thin films on sapphire substrates, which were deposited by magnetron sputtering, was around 36 K. Using a magnetization technique, the film's critical current density was estimated as J C = 1.8 × 107 А/cm2 at 10 K, J C = 8 × 106 А/m 2 at 20 K in a zero magnetic field B, and J C = 3 × 106 А/m2 at 10 K and B = 5 T. The values of the upper critical magnetic field B c2 and the irreversibility field B irr estimated using the four-probe technique were B C2(22 K) = 15 T when H||film surface, 11 T when H⊥film surface, and B irr(22 K) = 11 T when H||film surface. The X-ray study showed that the microstructure of the film contains only MgB2 and MgO (in minority). The SEM and EPXMA study and quantitative Auger spectroscopy analysis revealed periodical variations of the film composition on the nanolevel and the presence of (mainly) two intercalated Mg-B-O-C phases of slightly different, especially in oxygen content, and thus with different conductivity and, possibly, with different T C. The characteristics of superconducting magnesium diboride films make them promising for application in electronic devices, e.g., as high-pass filters.

Considerable attention has been paid recently to the development of comprehensive recycling of industrial wastewater, which provides for an appropriate degree of purification for both organization of circulation water supply, and subsequent disposal of waste of water treatment. The improved ferritization process, which allows decreasing original concentration of nickel ions in depleted electrolytes of nickel plating from 50–100 g/dm 3 to

The effects of the additions of powdered titanium carbide (TiC) and polyvalent titanium oxides (Ti-O) to MgB2 (synthesized under high pressure (2 GPa)–high temperature (800 and 1050 °C) conditions) on the critical current density, j c, critical magnetic fields, B C2 and B irr, and the related transformations in the materials structures are reported in this paper. The superconducting characteristics are compared with that of MgB2 with titanium (Ti) additions synthesized under the same conditions. The synthesis temperature, the ability of Ti-containing compounds to act as a getter, and the different diffusion rates of Mg and B into grains of these additions influence the distribution of the elements (boron, magnesium, and impurity oxygen) in the structures of MgB2-based materials. This in turn affects the formation of pinning centers, the resulting flux pinning and eventually the superconducting properties ( j c, B C2, B irr).

The electrical and thermal conductivity of the sample containing 97% by volume of the Ti3AlC2 MAX phase and 3% volume TiC was experimentally studied in the temperature range 15–300 K. The temperature dependence of the electrical resistance is approximated by a relation that takes into account the scattering of electrons by phonons and defects. The temperature dependence of the thermal conductivity shows a maximum at about 75 K. In the region of elastic scattering of electrons, the phonon and electron heat transfer are separated. With increasing temperature, the fraction of phonon heat transfer decreases from ∼90% at low temperatures to ∼40% near room temperature.

International audience; The Ti3AlC2-, (Ti,Nb)3AlC2- and Ti2AlC-based materials turned out to be more resistant than Crofer JDAsteel in oxidizing atmosphere as 1000 h long tests at 600◦C have shown. But the amounts of oxygen absorbed bythe materials during testing were different. The Ti2AlC-based material demonstrated the lowest oxygen uptake,(Ti,Nb)3AlC2-based absorbed a somewhat higher amount and the highest amount was absorbed by Ti3AlC2-basedmaterial. Scanning electron microscopy and the Auger study witnessed that amounts of oxygen in the MAXphases before the exposure in air were as well different: the approximate stoichiometries of the matrix phases ofmaterials were Ti3.1−3.2AlC2−2.2, Ti1.9−4Nb0.06−0.1AlC1.6−2.2O0.1−1.2and Ti2.3−3.6AlC1−1.9O0.2−0.6, respectively.The higher amount of oxygen present in the MAX phase structures may be the reason for higher resistanceto oxidation during long-term heating in air at elevated temperature. The studied materials demonstrated highstabilities in hydrogen atmosphere as well. The bending strength of the Ti3AlC2- and (Ti,Nb)3AlC2-based materialsafter keeping at 600◦C in air and hydrogen increased by 10–15%, but the highest absolute value of bending strengthbefore and after being kept in air and hydrogen demonstrated the Ti2AlC-based material (about 590 MPa).

Our investigations show that the addition of Ti, polyvalent titanium oxides or TiC powders (0.1-40 mm, amount: 10 wt%) can affect the formation of MgBx (x³4) inclusions and a redistribution of admixed oxygen resulting in the appearance of dispersed inclusions with near MgBO stoichiometry in the MgB2 matrix and thus influencing the critical current density and the critical magnetic fields of the materials. The highest Bc2 and Birr were obtained when powdered polyvalent titanium oxides (synthesized by electroerosion dispersion) or powdered titanium were added, but the critical magnetic fields were somewhat lower in the case of Ti additions. We show that Mg diffuses during the synthesis inside the grains of polyvalent titanium oxide, titanium carbide or titanium, which can affect the redistribution of boron and oxygen in the superconducting matrices and thus influence pinning and the superconducting properties.

Boron carbide (B4C) is normally known as a structural ceramic with excellent mechanical properties. Herein, the application of graphene-layer-coated B4C nanosheets (B4C@GN NSs) as efficient electromagnetic (EM) wave absorption materials was reported for the first time. B4C@GN NSs grew via the vapor–solid (VS) mechanism and coated with an ultrathin graphene layer through annealing. In addition to its graphene shell, the B4C@GN NSs had a unique small-sized nanosheet structure with a single sheet thickness of less than 50 nm. Concurrently, B4C micro- and nanoparticles were purchased or prepared to compare the morphologies and performances of several kinds of different B4C materials via characterization and analyses. The comparison revealed that the novel B4C@GN NSs possessed a special structure and a unique graphene shell that led to the great improvement in EM wave absorption. With a thickness of 1.19 mm, the B4C@GN NSs exhibited a minimal reflection loss (RLmin) of − 24.6 dB and a broad effective absorption bandwidth of 3.9 GHz. The electronic structure was analyzed by XANES to clarify the mechanism. The above results proved B4C@GN NSs to be an expectant absorber. The development of B4C@GN NSs might lay a theoretical foundation for the functionalization of structural ceramic materials.

This paper describes the established correlations between the characteristics of MgB2-based superconducting materials and their structural features, in particular the oxygen distribution and content. As indicated by SEM and Auger analysis, a sizeable amount of oxygen is usually present in superconducting MgB2 -based materials (bulks, thin films, and wires). The matrix phase of bulk MgB2 contains rather small amounts of oxygen, but contains a high amount of dispersed inclusions or areas with compositions close to MgBO. X-ray phase analysis with Rietveld refinement (using the FullProf Suite program package) of several highly dense MgB2 -based bulk samples (with high critical current densities) showed that the superconducting phase had a composition within the range MgB1.68O0.26 and MgB1.74O0.32 instead of pure MgB2 . Besides, a small amount of a phase with MgO structure was observed in the materials by X-rays as well. The calculation of the enthalpy of formation confirms the possibility of oxygen solubility in MgB2 and shows that the formation of MgB1.75B0.25 is most favorable. The results of ab initio calculations of the electronic structure and stability of the MgB2 compounds with partial oxygen substitution for boron show that it is energetically preferable for oxygen atoms to replace boron pairwise.

We have studied thin-film superconductor - semiconductor (with quantum dots)—superconductor MоRe–Si(W)—MoRe junctions, where electrons are tunneling through a single or several quantum dots within the Si(W) barrier. Current–voltage characteristics (CVCs) of the samples have been measured in a wide voltage range from –900 to 900 mV at temperatures from 4.2 to 8 K. At relatively high tungsten content in the barrier, we have observed emergence of the Josephson effect. Characteristic voltages I $_{c}$ R $_{N}$ , the product of the critical Josephson supercurrent I $_{c}$ and the normal-state resistance R $_{N}$ , of the samples were unusually high. Simultaneously, we have observed large excess quasiparticle currents I exc in the dissipative part of CVCs, which is a strong evidence of intensive electron-to-hole Andreev reflections in the junctions studied. When the W content in the barrier was decreased, the Josephson current disappeared, and we have observed resonant current peaks in the CVCs at bias voltages from 40 to 300 mV, which were symmetrical for positive and negative voltages. In the studied heterostructures, metal clusters inside the barrier behave as quasi-one-dimensional quantum dots; hence, the charge transport can be adequately described by scattering matrices within the quantum model of one-dimensional charge transport.

The results are presented on the investigation of the structure and mechanical properties of hot-pressed materials based on AlB12C2 powders of sizes 50–150 nm. It is shown that the consolidated materials having mechanical properties comparable with boron carbide may be produced at essentially lower (by 270–300°C) sintering temperatures. It has been established that the heating rate at compressing affects the stoichiometry of the impurity phase containing Al, B, O, which define the difference in mechanical properties of the materials (a decrease of the heating rate results in the insignifical decrease of the material hardness and increase of the fracture toughness).

In the paper, the research results o nanostructural composite ZrO2 – WC obtained with modified Field Assisted Sintering is described. Hot pressing processes were performed at different sintering temperatures using mixtures of different proportions of tungsten monocarbide, such as 10 wt%, 20 wt%., 30 wt%. Sintering process activated by alternating current provided good results in short time of 2 min at pressure 30 MPa and temperature 1350 °C. Reduced temperature and shorter sintering time prevented grains from growth, ensuring enhanced mechanical properties of the composite. The test campaign included analysis of shrinkage process and respective porosity of obtained composite, analysis of bulk material structure, especially dimensions and composition of grains, as well as analysis of mechanical properties, such as microhardness and fracture toughness. Analysis of wear resistance was performed in real work conditions, comparing the nozzles made from different materials working in an abrasive waterjet machining system. Even though the mechanical properties of the sintered ZrO2 – WC material was comparable to the other reported methods and compositions, the proposed modified Field Assisted method consumed much less energy and time. The most remarkable result was obtained for wear resistance, where the tested nozzle worked almost two times longer than the ones available in the market.

The paper presents an analysis of the properties of bulk superconducting magnesium diboride-based materials obtained by heating at high quasi-hydrostatic pressures (1–2 GPa), hot pressing (30 MPa), spark plasma sintering (16–96 MPa) and loose powder sintering. It is shown that the optimization of impurity distribution in MgB2 can be achieved by varying the synthesis conditions and introducing dopants. In particular, polycrystalline MgB2 materials synthesized at 2 GPa and containing a high amount of impurity oxygen demonstrates high critical current densities (106 and 103 A/cm2 at 20 K in magnetic fields of 1 and 8.5 T, respectively). It is found that the oxygen impurities are mainly localized in nanolayers or nanoinclusions, homogeneously distributed in the matrix. They act as pinning centers, while the MgB2 matrix also contains small amounts of dissolved oxygen. Impurity or intentionally added carbon entering the magnesium diboride structure leads to an increase in the critical magnetic fields up to Bc2 ...

Fault current limiters (FCL) require superconducting (SC) materials which can provide a definite rate of response to a fault event resulting in the SC – normal state reversible transition. The main characteristics determined the material suitability are the critical current density, jc, thermal conductivity and capacity which are strongly determined by manufacturing technology, in particular, of MgB2. In the paper we estimate the jc of bulk MgB2 samples by the vibrating magnetometer and inductive, contactless transformer, method using ring samples. The bulk MgB2 samples were produced under 30 MPa (hot pressing) and 2 GPa (quasihydrostatic pressing) at 800-1050 оС from different initial ingredients (Mg and B or MgB2 with and without additions). It is shown that the technology process and initial ingredients strongly influence the distribution of boron-and oxygen-enriched nanosized inhomogenities in MgB2 matrix, connectivity between SC grains, material porosity and, as result, the SC properties. The transformer method gives the jc in the range from 1.6·104 up to 6.3·104 A/cm2 at about 4 K while using magnetometer measurements the jc is estimated from 2.24·105 up to 5.1·105 A/cm2 at 10 K in self-magnetic fields. The contradictions in the jc estimated by different methods can be explained by instability of the SC state of MgB2, caused by variation of the applied magnetic field. Using the transformer method AC losses per a cycle before quenching for the best materials were estimated around 0.75-1 J/cm3, while the power of losses was about 200 W. The FCL model with rings cut out from SC MgB2 materials prepared using various technologies demonstrated that MgB2 is a promising material for application in inductive FCLs.

Comprehensive experimental results of fully oxidized (up to YBa2Cu3O6,9-7) melt-textured YBaCuO materials with different microstructures are presented. These microstructures are built respectively: (1) with a high dislocations density but almost without twins (after high temperature treatment at 2 GPa) and (2) with a high twin density, but practically free from dislocations and stacking faults (after high temperature oxygenation at 10-16 MPa). It is shown that for attaining high critical current densities and fields of irreversibility (jc(H‖c, 0 T)=9·104 A/cm2, H irr=9.7 T at 77 K), a high twin density in YBa2Cu3O6.9-7 matrix of MT-YBCO is required. The density of twins in fully oxidized materials depends on the distances between Y2BaCuO5 inclusions, larger twin densities are related to shorter distances between inclusions. The influence of phase composition of the initial powder mixtures on the distances between Y2BaCuO5 inclusions have been characterized and discussed.

The paper presents the results of studying the structure, phase composition, relieph, and superconducting characteristics of oxygen-containing thin films of magnesium diboride (MgB 2 )deposited on a dielectric substrate by magnetron sputtering of diboride-magnesium targets. The possibility of forming films of varying degrees of crystalline perfection and phase composition in the process of precipitation and annealing is shown, depending on the conditions of deposition and annealing. In the films, it is possible to realize various combinations of the Abrikosov vortex pinning centers (in the places of fluctuations of the critical temperature of the superconducting transition (T c -type)and in the places of fluctuations in the mean free path (I-type)), whose origin and density are influenced by the conditions for the synthesis of films. It is shown that the deposited films consist of a superconducting matrix, which is a solid solution of oxygen in a lattice of magnesium diboride of the MgB x O y type; the density of the superconducting critical current of the films can reach 1.8 ⨯ 1011−8.2 ⨯ 1010 A/m2 at 10 K and 8⨯1010 −2.8⨯1010 A/m2 at 20 K in fields of 0−1 T (when the external magnetic field is oriented perpendicular to the plane of the substrate).

The mechanical properties and temperature stability in air and hydrogen of the highly dense (ρ=4.27 g/cm3, porosity 1 %) material based on nanolaminated MAX phase Ti3AlC2 (89 % Ti3AlC2, 6 % TiC, 5 % Al2O3) manufactured by hot pressing (at 30 MPa) have been investigated. At room temperature the samplesexhibited microhardness HV = 4.6 GPa (at 5 N), hardness HV50 = 630 MPa (at 50 N ) and HRA=70 (at 600 N), Young modulus was 140 ± 29 GPa, fracture toughness K1C=10.2 MPa·m0.5compression strength 700 MPa and bending strength 500 MPa. After 1000 hours of exposition at 600 °C the oxide film (containing mainly Al2O3 and TiO2) formed on the surface and material demonstrated a higher oxidation resistance than chromium ferrite steels. Due to the surface oxidation the defects self-healing took place and the bending strength of the porous Ti3AlC2 (22% porosity) after exposition for 3 h at 600 oC in air slightly (for 3%) increased as compared to that at 20 oC. Besides, the porous Ti3AlC2 material resisted to high-temperature creep and after being kept in H2 at 600 °C for 3h its bending strength reduced by 5 %.

MgB 2 -based bulk materials synthesized under 30 MPa-2 GPa pressure demonstrated an enhanced connectivity A F ~50%-98%,as compared tomostother reports (below50%), and a shielding fraction of 75%-100%. The materials inhibit high critical current densities j c , but no strict correlation was found between A F and j c . On the other side, we found correlations between jc and the distribution of nanostructural inhomogeneities such as impurity oxygen in the form of oxygen-enriched Mg-B-O nanolayers or nanoinclusions and its solution in the MgB 2 matrix and as well with the amount and size of higher magnesium borides MgB x , x ≥ 4 inclusions. The distribution of boron- and oxygen-enriched (as compared to stoichiometric MgB 2 ) inhomogeneities affects the type of pinning and, thus, jc, and to some extent, it can be regulated by synthesis temperatures and pressures and by Ti addition. Auger spectroscopy, scanning electron microscopy, and X-ray with Rietveld refinement were used for structural study.

The authors of this paper have substantiated the appropriateness of application of polishing suspensions of diamond micron powders, boron nitride and Ti3AlC2 MAX-phase powders in the study of the mechanism of polishing monocrystalline silicon carbide. They have proved suitability of using the following parameters as criteria for efficiency of the machining process: the specific value of the energy of transfer, the density of the energy of transfer, and the density of vibrational energy spent for the formation of debris particles. Computer modeling of the polished surface micro- and nanoprofile produced the profile charts from which the surface roughness parameters have been determined and the characteristic relations between the parameters and the most probable debris particle size have been defined.

Compacting powders based on MAX phases was carried out by shock-wave loading. Six experimental samples of Ti2AlC and Ti3AlC2 were obtained. Shock-wave compression was carried out by using industrial low-blasting explosives on planar configuration. Analysis of phase composition and density of the samples after compacting showed that material has a high content of MAX phase (∼ 96 wt.% for Ti2AlC and more 79 wt.% for Ti3AlC2). Theoretical density has not been achieved and porosity of samples was in the range from 13 to 18%. Microhardness over surface of compacts at loading was in the range from 450 to 690 MPa. Average microhardness value over depth was 801 MPa. Thus, destruction of MAX phase during shock-wave loading doesn’t occur. However, consolidation was uneven.

The high pressure (50 MPa - 2 GPa) – high temperature synthesized MgB2 bulk materials are characterized by nearly theoretical density (1-2% porosity), 80-98% connectivity, extremely high critical current densities (e.g. at 20 K, in 0–1 T jc=1.3–1.0 MA·cm-2 (with 10% SiC) and jc= 0.92 – 0.73 MA·cm-2 (without doping)), large irreversibility fields (Birr(18.4 K) =15 T and Birr (0 K) = 32.5 T) and high upper critical fields (Bc2 (22 K) =15 T and Bc2(0 K) ~ 42.1 T). The transformation of grain boundary pinning to point pinning in MgB2-based materials with increasing manufacturing temperature (from 800 to 1050 oC) under pressures from 0.1 to 2 GPa correlates well with an increase in critical current density in low external magnetic fields caused by the redistribution of boron and the oxygen impurities in the material structure. As the manufacturing temperature increases, the discontinuous oxygen enriched layers transform into distinct Mg-B-O inclusions and the size and amount of inclusions of higher magnesium borides MgBX (X>4) are reduced. The effect of oxygen and boron redistribution can be enhanced by Ti or SiC additions.

Thermogravimetry and differential thermal analysis have been used to study the resistance to the air oxidation of high-density samples of Ti3AlC2, Ti2AlC and Ti2Al(C1−xNx) solid solutions. It has been shown that the Ti3AlC2 samples are more stable than Ti2AlC and Ti2Al(C1−xNx) solid solutions and as the nitrogen content of the solid solution increases to x = 0.75, the oxidation resistance decreases. The following characteristics have been exhibited by the material containing 89 wt % Ti3AlC2 (the rest being Al2O3 and TiC) having density 99% of theoretical: bending strength Rbm = 500 MPa, compressive strength Rcm = 700 MPa, fracture toughness KIc = 10.2 MPa·m0.5, hardness HRA = 70 GPa, HV = 4.6 GPa, Young modulus = 149.4 ± 28.7 GPa. After sintering with diamonds or cBN (50 wt %) at 5.5–7.7 GPa and 1350–1960°C for 0.07–1.0 h the Ti3AlC2 MAX phase decomposes to form TiC and TiAl or TiB2 and a thin layer of Al4C3 forms at the interface with diamond. The Al4C3 decomposition in a composite material due to the interaction with the air moisture results in the crack initiation along the diamond perimeter, which brings about the material fracture in 1–2 weeks. It has been found that the Ti3AlC2 powder is efficient for polishing natural and synthetic jewelry crystals and competitive in polishing efficiency and quality with ACM 2/1 grade diamond.

The superconducting characteristics, such as the critical current density and the critical magnetic fields, of MgB2-based materials, which in fact belong to the Mg-B-O system because of the high concentration of admixed oxygen (up to 17 wt. %), depend on the inhomogeneity of the oxygen and boron distribution, which can be controlled by the synthesis temperature (600-1200 oC) and pressure (up to 2 GPa) as well as by SiC and Ti additions (10 wt%). With increasing manufacturing temperature grain boundary pinning transforms into point pinning, which is well correlated with the transformation of discontinuous oxygen enriched layers into separately located Mg-B-O inclusions in the MgB2 nanostructure and with a reduction of the size and amount of inclusions of higher magnesium borides MgBX (X>2). Ti or SiC additions can influence the oxygen and boron distribution as SEM and Auger structural studies showed.

Magnesium diboride superconducting wires and bulk samples synthesized at high pressure have been produced with a variety of reactive metal additions. All these samples showed high critical current densities, but here we are most interested in the striking result that reactive metal additions such as titanium substantially improved the critical current values, but had little detrimental effect on Tc values. For instance, the critical current values in the wires could be increased by more than a factor of 3.5 at 4 K and 10 T by the inclusion of up to 10 wt% of Ti. In bulk materials the J c values can be increased by even larger values, and the irreversibility field at 20 K increased to above 7 T. In a detailed study of the microstructure of these materials we have shown that PIT ex situ wires with 10 wt% titanium additions have a complicated layered microstructure around the Ti-rich particles, possibly forming titanium-boron phases, but also incorporating impurity elements including hydrogen. X-ray diffraction data, TEM and elemental mapping in the NanoSIMS confirmed the surprising suggestion that samples synthesized at high pressure from Mg and B with Ti additions contain a titanium hydride. These new compositional data support the idea that reactive metal additions are extremely beneficial in MgB2 wires and bulk materials because they preferentially adsorb deleterious impurities from the superconducting matrix. © 2005 IOP Publishing Ltd.

The relevant pinning centers of Abrikosov vortices in MgB$_{2}$–based materials are oxygen-enriched Mg-B-O inclusions or nanolayers and inclusions of MgB$_{x}$ (x>4) phases. The high critical current densities, j$_{c}$, of 10$^{6}$ and 10$^{3}$A/cm$^{2}$ at 1 and 8.5 T, respectively, at 20 K can be achieved in polycrystalline materials (prepared at 2 GPa) containing a large amount of admixed oxygen. Besides, oxygen can be incorporated into the MgB$_{2}$ structure in small amounts (MgB$_{1.5}$O$_{0.5}$), which is supported by Auger studies and calculations of the DOS and the binding energy. The j$_{c}$ of melt textured YBa$_{2}$Cu$_{3}$O$_{7-δ }$ (or Y123)-based superconductors (MT-YBaCuO) depends not only on the perfectness of texture and the amount of oxygen in the Y123 structure, but also on the density of twins and micro-cracks formed during the oxygenation (due to shrinking of the c-lattice parameter). The density of twins and microcracks increases with the reduction of the distance between Y$_{2}$BaCuO$_{5}$ (Y211) inclusions in Y123. At 77 K j$_{c}$=8⋅10$^{4}$ A/cm$^{2}$ in self-field and j$_{c}$=10$^{3}$ A/cm$^{2}$ at 10 Т were found in materials oxygenated at 16 MPa for 3 days with a density of twins of 22–35 per μm (thickness of the lamellae: 45-30 nm) and a density of micro-cracks of 200–280 per mm. Pinning can occur at the points of intersection between the Y123 twin planes and the Y211 inclusions. MTYBaCuO at 77 K can trap 1.4 T (38×38×17 mm, oxygenated at 0.1 MPa for 20 days) and 0.8 T (16 mm in diameter and 10 mm thick with 0.45 mm holes oxygenated at 10 MPa for 53 h). The sensitivity of MgB$_{2}$ to magnetic field variations (flux jumps) complicates estimates of the trapped field. At 20 K 1.8 T was found for a block of 30 mm in diameter and a thickness of 7.5 mm and 1.5 T (if the magnetic field was increased at a rate of 0.1 T) for a ring with dimensions 24×18 mm and a thickness of 8 mm.

International audience; Increasing the pressure during manufacturing MgB2 enhances the volume pinning force and moves the position of the maximum to higher magnetic fields. A similar shift was observed when Ti or SiC was added and the maximum of the volume pinning force was found at higher fields in in situ synthesized materials than in ex situ sintered samples. We attribute the observed changes to Mg–B–O oxygen-enriched regions and grains of higher magnesium borides in the MgB2 matrix. High-temperature processed materials demonstrated mainly point or mixed pinning while grain boundary pinning dominated after low-temperature synthesis.

It has been established that the oxygenation of the structure of YBa2Cu3O7−δ (Y123) textured ceramic materials under elevated pressure (up to 10–16 MPa) and high temperatures (700–900°C) for a relatively short time (72 h) makes it possible to attain the record superconducting (at 77 K in the ab plane of Y123 phase jc ≈ 100 kA/cm2 (0 T), 55 kA/cm2 (2 T) and Hirr 9.5 T) and mechanical (microhardness up to HV = 7.6 GPa and fracture toughness up to KIc = 4.4 MPa·m0.5 under 4.9 N) properties. The high material characteristics have been explained by the formation of a nanostructure from twins acting as pinning centers (the density of twinning being 20–35 m−1) and a considerably smaller amount of microcracks (< 0.2 m−1) as well as by prevention of macrocracking.

The results of experimental study of the critical current and AC losses in high pressure-synthesized MgB2bulk superconductors are presented. The method is based on the use of the transformer configuration and suitable for samples in the form of hollow superconducting cylinders and rings. It was shown that the critical current measured by the transformer method is an order of magnitude lower than the value given by the magnetization technique. The obtained dependencies of the losses on current and frequency reveal the deviations from the critical state model behavior and reflect structural peculiarities of the investigated MgB2samples.

Superconducting (SC) and mechanical properties of spark plasma (or SPS) produced MgB2 –based materials allow their efficient applications in fault current limiters, superconducting electromotors, pumps, generators, magnetic bearings, etc. The synthesized from Mg and B at 50 MPa, 1050 °C for 30 min material has a density of 2.52 g/cm3, critical current density, jc = 7.1•105 A/cm2 at 10 K , 5.4 •105 A/cm2 at 20 K, and 9•104 A/cm2 at 35 K in zero magnetic field; at 20 K its field of irreversibility Birr(20)=7 T and upper critical field Bc2(20)=11 T; microhardness HV=10.5 GPa and fracture toughness K1C =1.7 MPa•m1/2 at 4.9 N-load. SPS-manufactured in- situ MgB2-based materials usually have somewhat higher jc than sintered ex-situ. The pressure variations from 16 to 96 MPa during the SPS-process did not affect material SC characteristics significantly; the jc at 10-20 K was slightly higher and the material density was higher by 11%, when pressures of 50-96 MPa were used. The structure of SPS-produced MgB2 material contains Mg-B-O inclusions and inclusions of higher borides (of compositions near MgB4, MgB7, MgB12, MgB17, MgB20), which can be pinning centers. The presence of higher borides in the MgB2 structure can be revealed by the SEM and Raman spectroscopy.

By studies of materials based on the Ti3AlC2 MAX phase containing inclusions of titanium carbide it has been shown that as a titanium carbide content increases from 2 to 99%, the nanohardness and Young modulus of the material increase from 2.0 ± 0.4 to 23.6 ± 1.2 GPa and from 137 ± 21 to 447 ± 11 GPa, respectively. The exponent in the equation of creep for these samples has been found to vary from 104 to 140, which indicates that mechanical properties of the material and, hence, of the Ti3AlC2 MAX phase depend on the strain rate only slightly. The formation of broad hysteresis loops has been observed in the cyclic loading/unloading of the indenter for samples consisting mainly of the Ti3AlC2 MAX phase. This points to serious losses in elastic energy of the MAX phase in strain cycling and, hence, the prospects of the MAX phase application as a damping material. It has been found that the microhardness of a sample consisting of 98% Ti3AlC2 produced by sintering under a load of 4.9 N was 2.1 GPa and its fracture toughness was high (no cracks from the indent corners were observed even under a load of 149 N). Microhardness and fracture toughness of the material consisting of 71% Ti3AlC, 6% Ti2AlC, and 23% TiC were 3.0 ± 0.6 GPa and 4.3 ± 1.4 MPa·m1/2, respectively.