Abstract Signs of overdoping were observed on the superconducting GdBa 2 Cu 3 O 7-δ (GdBCO) layers of commercially produced coated conductors (CC) after a re-oxygenation through the thin (2 μm) silver layer at oxygen pressures of 100-160 bar, and 600-800 °C. An increase in the charge carrier density n H (100 K) up to 7.86×10 21 cm −3 , a decrease in the c -lattice parameters of GdBCO down to 1.1715(5) nm, a peak in the normalized resistivity close to the transition temperature are compatible with an increase of oxygen doping level up to p = 0.1740. Consequently, the self-field critical current density ( J c ) at 77 K increased by 21.5% to J c = 2.7 MA/cm 2 after reoxygenation at 160 bar oxygen at 800 °C for 3 h. At 5 K in the self-field, J c of this sample reached 30.2 MA/cm 2 . Its superconducting GdBCO layer was characterized by the parameter c =1.1727(1) nm, the superconducting transition temperature T c =92.63 K, the charge carrier density n H (100 K)=7.3×10 21 cm −3 , and the oxygen doping of its CuO planes was p =0.1727.

Amorphous highly conductive coatings Ti-Al-C, (Ti,Mo)-Al-C and (Ti,Cr)-Al-C were deposited on titanium alloy substrates by hybrid magnetron using T2AlC and Ti3AlC2 MAX-phases-based targets and in parallel cathode-arc evaporation of Mo or Cr targets. The (Ti,Cr)-Al-C coating showed the highest electrochemical corrosion resistance among all deposited coatings in 3.5 wt% NaCl aqueous solution at 25 degrees C: corrosion potential Ecorr = 0.044 V vs. saturated calomel electrode, corrosion current density icorr = 2.48 x 10-9 A/cm2. The (Ti,Cr)-Al-C coating also demonstrated the highest long-term oxidation resistance, and after heating in air at 600 degrees C for 1000 h, its surface electrical conductivity became even slightly higher after long-term heating: increased from sigma = 9.84 x 106 S/m to sigma = 4.35 x 105 S/m, which is explained by the crystallization of the amorphous coating during heating process. The nanohardness and Young's modulus of the coating after deposition were within 15 GPa and 240 GPa, respectively. The hybrid magnetron deposited (Ti,Cr)-Al-C coatings can be used to protect interconnects in lightweight molten carbonate fuel cells elements.

The electromagnetic characteristics, particularly the real εr′ and imaginary εr″ parts of the dielectric constant, of new AlN-based composites with additions of powdered diamond, soot, and diamond with 3–5 wt.

Treatment of GdBCO_CC under 100 bar of O 2 at 600 °C for 3 h led to an increase in J c (77K, 0 T) by 6% up to 2.67 MA/cm 2 and a decrease in the c-parameter of Gd123 to 1.17310 nm, which may be associated with its overdoping with oxygen (the charge carrier density in superconducting Gd123 layer was 6.91×10 21 cm 3 ). No strong correlation was observed between J c , T c , c-parameter of RE123 (RE=Eu, Gd) and carrier density n H of EuBCO_CC and GdBCO_CC treated at 300-800 °C, 1-160 bar O 2 for 3-12 h.

To study the possibility of overdoping with oxygen and, thus, an increase in the charge carrier density, n(H)(100 K), in RE123 layers (RE = Eu, Gd) with the aim of increasing the critical current density, Jc, oxygenation was carried out in the pressure range of p(O2) = 1-160 bar and temperatures of T-S = 300-800 degrees C during tau = 3-12 h of commercial EuBCO and GdBCO coated conductors (CC), from which the protective Cu layer and, in half of the cases, the Ag layer were chemically removed before oxygenation. The evidences of overdoping were observed about what were witnessed an increase of n(H)(100 K), reduction of c-lattice parameters of RE123 (RE = Eu, Gd) of superconducting layers, behavior of normalized resistivity before superconducting transition, and J(c) variation, however, the conditions to achieve optimal doping were not found yet. Treatment under 100 bar of O-2 for 3 h of GdBCO_CC (with Ag layer) at 600 degrees C led to an increase in J(c) (77 K, 0 T) from 2.57 to 2.67 MA/cm(2), n(H)(100 K) increased from 6.55 x 10(21) to 6.91 x 10(21) cm(-3), and J(c)(5 K, 0 T) = 28.94 MA/cm(2) was observed after the treatment. The increase in J(c) (77 K, 0 T) from 2.10 to 2.28 MA/cm(2) for GdBCO_CC (without Ag layer) was observed after treatment at 300 degrees C under 100 bar of O-2 for 3 h. In the both cases c-parameter of Gd123 decreased from 1.1735(1) to 1.1731(0) nm. For EuBCO_& Scy;& Scy; after treatment a decrease in c-parameters of Eu123 was observed: from 1.1738(8) to 1.1734(5) nm (for the Ag-coated sample under 100 bar O-2 at 300 degrees C) and from 1.1740(2) to 1.1736(3) nm (for the sample without Ag under 160 bar O-2 at 800 degrees C), but we failed to increase n(H)(100 K) and J(c) of the studied samples. However, the studies are still ongoing.

Abstract—For structurally homotypical specimens different in the ZrO2 content from the (94WC–6Co) + ZrO2 matrix material used in diamond-containing Сdiamond–(WC–Co) composites formed by spark plasma sintering, the dependences of the relative density ρrel, the ultimate strength under compression Rcm and bending Rbm, the microhardness НV, and the fracture toughness KIс on the zirconia content have been established. The addition of 6 wt

The study is devoted to the electrodynamic properties of composite materials based on AlN–5 wt

The intensive development of hydrogen technologies has made very promising applications of one of the cheapest and easily produced bulk MgB2-based superconductors. These materials are capable of operating effectively at liquid hydrogen temperatures (around 20 K) and are used as elements in various devices, such as magnets, magnetic bearings, fault current limiters, electrical motors, and generators. These applications require mechanically and chemically stable materials with high superconducting characteristics. This review considers the results of superconducting and structural property studies of MgB2-based bulk materials prepared under different pressure–temperature conditions using different promising methods: hot pressing (30 MPa), spark plasma sintering (16–96 MPa), and high quasi-hydrostatic pressures (2 GPa). Much attention has been paid to the study of the correlation between the manufacturing pressure–temperature conditions and superconducting characteristics. The influence of the amount and distribution of oxygen impurity and an excess of boron on superconducting characteristics is analyzed. The dependence of superconducting characteristics on the various additions and changes in material structure caused by these additions are discussed. It is shown that different production conditions and additions improve the superconducting MgB2 bulk properties for various ranges of temperature and magnetic fields, and the optimal technology may be selected according to the application requirements. We briefly discuss the possible applications of MgB2 superconductors in devices, such as fault current limiters and electric machines.

Superconductivity in a nitride of the MAX-phase family was reported by A.D. Bortolozo et al. in Ti 2 InN ( a = 0.3074 nm, c = 1.3975 nm) with a transition temperature of 7.3 K. In this study, we report on Ti 2 InN MAX phase-based samples (with up to 94 wt.% of Ti 2 InN) synthesized by several methods, which, unfortunately, did not comply with bulk superconductivity of this compound. The Ti 2 InN materials were synthesized from Ti 2 InN precursor powder of 93-95 wt.% purity (obtained by the method proposed by A.D. Bortolozo et al. [1]) according to the following routes: (1) at 130 bar of N 2 , leading to 54 wt.% of Ti 2 InN ( a = 0.3076(1), c = 1.4012(5) nm); (2) in a sealed quartz ampoule in Ar, (88.5 wt.% Ti 2 InN, a = 0.3076(1), c = 1.4012(4) nm); (3) by spark plasma sintering (SPS) in contact with hBN at 45 MPa (94 wt.% Ti 2 InN, a = 0.3077(7), c = 1.4021(5) nm), and (4) by high quasihydrostatic pressure - high temperature sintering (HP-HT) in contact with hBN at 4 GPa (83.5 wt.% Ti 2 InN, a = 0.3075(3), c = 1.4017(5) nm). Despite all the manufactured samples demonstrated superconducting behaviour with T c (onset) near 5 K and the samples prepared by SPS and HP-HT methods were highly dense, a very broad magnetic transition (ac susceptibility) not saturating down to 2 K has been observed. No macroscopic Meissner phase was established and the magnetization was far too weak to evidence bulk superconductivity of the entire sample and hence of Ti 2 InN. However, a superconducting gap of about 1.2 - 2.1 mV was derived from point-contact spectroscopy at some areas of HP-HT sintered samples. The dispersed crystalline admixture grains of TiN phase in Ti 2 InN matrices of our samples or a metallic In-alloy are most probable candidates for the superconducting phase in our materials.

The work describes the creation hard AlB12C2-based ceramic materials under by hot pressing and by high pressure-high temperature conditions. The high mechanical performance of the materials we obtained are similar to those of boron carbide, which can be explained by the structural features of B4C and AlB12/ AlB12C2 [1], namely the presence of almost identical structural elements - regular icosahedrons of boron atoms. The possibility of modifying the structure and properties by introducing additives became the reason for conducting research. To obtain the material, sintering of a powder mixture of of αAlB12 and SiC was used. Relatively cheap nanopowders (50-150 nm, with a specific surface area of 21-15 m2/g) α-AlB12 synthesized by PhD. V.B. Muratov (IPM NASU) were used in work [2]. The hot pressing at 30 MPa 1800-1970 оC of two compounds from α-AlB12 nanopowder with 15 (I) and 20 (II) wt.% SiC addition can result in formation of ceramic elements having according x-ray an-is 88 wt.% AlB12C2-12 wt.% Al2O3-SiC(additives) and 85.5 wt.% AlB12C2-14.5 wt.% Al2O3-SiC(additives) phases compositions respectively. Both materials turned out to be light (density rI=2.6 and rII=2.36 g/cm3) and quite dense (porosity PI=5 %; PII=8 %). Samples of the first (I) material were demonstrated HV - 23.3 GPa hardness, fracture toughness K1c - 5.0 MPa•m0.5 and samples of the second (II) material showed HV - 25.6 GPa, K1c - 5.7 MPa•m0.5 accordingly. The sintering under high-pressure apparatus at 4,1 GPa generally allows to reduce sintering temperatures. At a reduced temperature to 1700 oC at 4.1 GPa and holding for 8 min, the samples were perfect on the outside, but with a large amount of internal stress. This material had hardness HV - 25.2 GPa and fracture toughness K1c - 4.2 MPa•m0.5 at density rIIІ=2.75 g/cm3 and porosity PIII=5 %. High performance characteristics of the obtained composites can be explained by the formation of solid solutions in the structure.

This paper presents the results of the experimental research on diamond-reinforced composites with WC–Co matrices enhanced with a ZrO2 additive. The samples were prepared using a modified spark plasma sintering method with a directly applied alternating current. The structure and performance of the basic composite 94 wt.%WC–6 wt.%Co was compared with the ones with ZrO2 added in proportions up to 10 wt.%. It was demonstrated that an increase in zirconia content contributed to the intense refinement of the phase components. The composite 25 wt.%Cdiamond–70.5 wt.%WC–4.5 wt.%Co consisted of a hexagonal WC phase with lattice parameters a = 0.2906 nm and c = 0.2837 nm, a cubic phase (a = 1.1112 nm), hexagonal graphite phase (a = 0.2464 nm, c = 0.6711 nm), as well as diamond grits. After the addition of zirconia nanopowder, the sintered composite contained structural WC and Co3W3C phases, amorphous carbon, tetragonal phase t-ZrO2 (a = 0.36019 nm, c = 0.5174 nm), and diamond grits—these structural changes, after an addition of 6 wt.% ZrO2 contributed to an increase in the fracture toughness by more than 20%, up to KIc = 16.9 ± 0.76 MPa·m0.5, with a negligible decrease in the hardness. Moreover, the composite exhibited an alteration of the destruction mechanism after the addition of zirconia, as well as enhanced forces holding the diamond grits in the matrix.

The structure, mechanical characteristics, and high-temperature stability in vacuum and air of ZrB 2 and HfB 2 -based materials sintered at a high quasi-hydrostatic pressure (4.1 GPa) under hot pressing (at a pressure of 30 MPa) with and without SiC and Si 3 N 4 additives have been studied. It has been shown that short-term sintering (4 min) under high pressure conditions and at a comparatively low temperature (1800°C) essentially improves the mechanical properties of these materials as compared to the similar materials synthesized by the other method (hot pressing and spark-plasma sintering). In the case of sintering at a high pressure (4.1 GPa), the addition of 20 wt % SiC to ZrB 2 and 30 wt % SiC to HfB 2 leads to a decrease in the specific gravity of ZrB 2 and HfB 2 and increases their hardness by 17 and 46% and fracture toughness by 40 and 21%, respectively. When SiC is added, there occurs the formation of solid solutions through the mutual diffusion of C and Si into the ZrB 2 or HfB 2 matrix phases and the slight diffusion of Zr and Hf into SiC-enriched areas. The improvement of the mechanical properties of ZrB 2 and HfB 2 sintered at a high pressure without additives is explained by the formation of stronger bonds between the sintered material grains. The addition of SiC to ZrB 2 slightly decreases the Young modulus, but increases the damping ability of the synthesized materials. The simultaneous addition of SiC and Si 3 N 4 to ZrB 2 leads to an increase in the hardness to a smaller extent, but results in a further increase in fracture toughness. The melting temperature in vacuum of sintered ZrB 2 and HfB 2 has proven to be much higher as compared to the materials with SiC additives. The composite material synthesized from a HfB 2 –30 wt % SiC mixture has a density ρ = 6.21 g/cm 3 , a microhardness H V (9.8 N) = 38.1 ± 1.4 GPa, H V (49 N) = 27.7 ± 0.24 GPa, H V (98 N) = 26.3 ± 2.03 GPa, and a fracture toughness K І с (9.8 N) = 8.2 ± 0.2 MPa m 0.5 , K І с (49 N) = 6.8 ± 0.6 MPa m 0.5 , K І с (98 N) = 6.4 ± 0.11 MPa m 0.5 , which are much higher than the similar characteristics of HfB 2 sintered under the same conditions, but without the additives.

Nanopowder of iron oxide (mainly Fe3O4) has been obtained by electroerosion dispersion method and was used for manufacturing of gradient polymer-based microwave absorbing materials which absorb (1) on 36.6 GHz with a level of absorption of 99% (with a maximum penetration -40 dB and reflection -23 dB) and (2) on 10 GHz and 36.6 GHz with an absorption of 90% and 98.4%, correspondently (with a maximum reflection -18 dB and -10 dB and penetration -40 dB and -60 dB, respectively). It was demonstrated, that change of magnetic properties of the absorbing material under mechanical load can be used for non-destructive control. Sintered under high pressure-high temperature conditions (2 GPa, at 900, 1000, 1100, 1200 and 1300 & DEG;C for 4 min) iron oxide nanopowder in presence of hexagonal boron nitride (hBN) demonstrated soft magnetic behavior. Electron Backscatter Diffraction (EBSD) study has showed that during sintering the grains have grown beyond the superparamagnetic size limit inspire short annealing time. The structure of sintered materials was investigated using X-ray diffraction with a full-profile fitting procedure. The materials sintered at 2 GPa at 900 and 1000 & DEG;C contained 75-80 wt% of FeO and 25-20 wt% Fe. Materials sintered at 1100 oC, along with 32 wt% FeO and 2 wt % Fe, contained a significant amount of Fe3N: 66 wt%. However, materials sintered at 1200-1300 & DEG;C contain almost pure Fe3N phase. Thus, under conditions of high pressures and temperatures with increasing sintering temperature, reduction of iron oxide was observed, followed by its nitriding with nitrogen released from the boron nitride, which led to a reduction of coercive force and thus improving soft magnetic characteristics of the sintered materials. The scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) study of the sample, sintered at 1300 oC showed approximate composition of Fe3N0.8C0.3-0.6O0.06-0.3.

The development of hydrogen energy and, in particular, high-performance submersible liquid hydrogen (LH) pumps requires superconducting bearings which can trap magnetic fields up to 1 T at 20 K. MgB 2 is hence a promising candidate for this application. The superconducting properties and microstructure of differently prepared MgB 2 were compared and the ability of different composite materials to trap magnetic fields was studied. Hollow cylinders of the same geometry were manufactured from hot pressed (under 30 MPa) blocks prepared from Mg:2B with Ti, TiC and Ti-O additives as well as from melt-textured YBCO ceramics. The high critical current densities and critical magnetic fields should ensure high trapped fields in all these materials. Indeed all materials demonstrated the required performance; however, flux jumps are a serious issue in MgB 2 even in crack free cylinders and impeded higher trapped fields.

The structure, mechanical characteristics, and high-temperature stability in vacuum and air of ZrB2 and HfB2-based materials sintered at a high quasi-hydrostatic pressure (4.1 GPa) under hot pressing (at a pressure of 30 MPa) with and without SiC and Si3N4 additives have been studied. It has been shown that short-term sintering (4 min) under high pressure conditions and at a comparatively low temperature (1800°C) essentially improves the mechanical properties of these materials as compared to the similar materials synthesized by the other method (hot pressing and spark-plasma sintering). In the case of sintering at a high pressure (4.1 GPa), the addition of 20 wt

The oxygen concentration and distribution in the microstructure of MgB 2 - and YBa 2 Cu 3 O 7-δ -based materials affect the formation of nanostructural defects and thus influence the critical current density, upper critical magnetic field and irreversibility field. For MgB 2 oxygen containing additions (Dy-O, Ti-O) in the form of nanograins occurred not to be very effective for an increase of critical current density, j c . Sn-O additions to MgB 2 can provoke even a significant decrease of j c due to a chemical interaction of Sn with MgB 2 . The processing pressure and temperature influence the defect density of the relevant pinning centers and the regularity of their distribution in doped and undoped MgB 2 as well as in MT-YBCO.

The effect of the concentration of vanadium nitride additive (in the range from 0 to 10 wt %) on the phase formation, hardness, and fracture toughness of composite diamond-containing materials based on the 51Fe–32Cu–9Ni–8Sn matrix molded by cold pressing and subsequent vacuum hot pressing is investigated. It is found that the addition of 10 wt % of vanadium nitride to the 51Fe–32Cu–9Ni–8Sn composite is accompanied by an increase in the hardness from 3.86 to 8.58 GPa with a slight decrease in the fracture toughness from 5.55 to 4.76 MPa m1/2. Moreover, the H(CVN) dependence has two characteristic segments that differ in the slope. The hardness increases insignificantly (from 3.86 to 5.26 GPa) in the range of 0 < CVN < 4 wt %, while the second region (CVN > 4 wt %) is characterized by a more substantial increase in the hardness and a more significant decrease in the grain size. It is shown that these parameters are achieved owing to the dispersion mechanism of strengthening and modification of the structure (a decrease in the mean particle size of the matrix phase, the formation of new (Fe3Ni)0.5 and Cu3Fe17 phases, and the precipitation of primary and secondary phases of vanadium nitride) and phase composition of the composites.

The magnetic characteristics of iron oxide nanopowder (Fe3O4 base phase) produced by electroerosion dispersion and consolidated at high pressures (2 GPa) and high temperatures (900, 1000, 1100, 1200, and 1300°C) for 0.07 h in contact with hexagonal boron nitride were studied. The nanopowder was produced by dispersing iron granules or shavings in plasma induced at contact points between the granules when electric pulses of high current and voltage were passed through them. The metal granules being dispersed are in a constantly circulating liquid (water) atmosphere, creating a pseudo-boiling layer from the granules. The liquid (water in this case) cools the granules to prevent them from being welded and oxidizes the metal vapors that emerge in plasma, forming nanosized iron oxide grains carried by the liquid flow into sedimentation tanks (powders with different grain sizes sediment in different tanks). Room-temperature studies of the magnetic characteristics of samples consolidated from iron oxide powders showed that the materials sintered at 1200 and 1300°C were soft magnetics with virtually zero hysteresis. Their specific magnetic moments at 5000 Oe were 128.4 and 126.4 emu/g and the coercive force was negligibly small: 5.1 and 4.5 Oe. The materials sintered at 1100°C were characterized by a specific magnetic moment of 90.4 emu/g and a relatively low coercive force of 9.1 Oe. The specific magnetic moments of the samples sintered at 900 and 1000°C were significantly lower and the coercive force higher: 40.2 and 42.1 emu/g and 37.9 and 32.4 Oe, respectively. X-ray diffraction with Rietveld refinement revealed that the materials consolidated at 900 and 1000°C contained 75–80 wt.% FeO and 25–20 wt.% Fe, while the materials sintered at 1100°C contained, along with 32 wt.% FeO and 2 wt.% Fe, a significant amount of Fe3N (66 wt.%). The materials consolidated at 1200–1300°C contained 100% Fe3N phase. Hence, under high pressures and increasing sintering temperatures, iron oxides are reduced and then iron is nitrided with nitrogen released from boron nitride, which improves the soft magnetic characteristics of the sintered materials.

By the method of cold pressing followed by vacuum hot pressing, samples of composite diamond-containing materials with a diameter of 10 mm and thickness of 8 mm based on WC–6%Co alloy containing different (from 0 to 10%) contents of chromium diboride, which physical and mechanical properties depend on the composition of the carbide matrix, were developed. The optimal concentrations of chromium diboride ( = 4 %) in the hard alloy composites sintered in a two-stage vacuum hot pressing mode at temperatures Т 1 = 1300 °С and Т 2 = 1400 °С, at which the highest values of physical and mechanical properties of composites ( К I c = 15.4 MPa∙m 1/2 , Н = 14.3 MPa, R bm = 2950 MPa and R cm = 5780 MPa) were achieved. The specified indicators result from the dispersed strengthening mechanism and structure modification (reduction of the average grain size of the carbide phase from 5.6 to 3.4 μm, disappearance of pores at the Co binding phase, formation of inhibitor phase clusters at the interphase boundaries) and the composites phase pattern. Furthermore, all sintered samples containing CrB 2 powder additives in the charge are characterized by a balanced phase distribution and dispersed structure as compared to the sample containing no CrB 2 powder additives.Exceeding 4% of CrB 2 content in a composite material deteriorates its mechanical properties associated with oxidation of tungsten carbide grains and the presence of W=O double bonds on the surface and at grain boundaries of amorphous or nanostructured tungsten oxide.

Some new data on the effect of chromium diboride additives (within a range from 0 to 10 wt %) on the phase formation and physicomechanical properties (fracture toughness, hardness, ultimate bending and compression strength) of composite materials based on the WC–6 wt % Co hard alloy formed by cold pressing with further vacuum hot pressing are reported. It has been revealed that the sintered samples of composites are composed of the structural phases of hexagonal WC and orthorhombic B2CoW2 groups and amorphous carbon inclusions. In this case, the parameters of crystalline B2CoW2 are varied depending on the CrB2 content. It has also been established that the addition of 4 wt % of chromium diboride to the WC–6Co composite leads to a two-fold increase in the fracture toughness (from KIc of 9.8 to 14.5 MPa m1/2) with a slight decrease in the hardness H from 15.1 to 13.9 GPa and also to an increase in the ultimate bending strength Rbm from 2000 to 2500 MPa and the ultimate compression strength Rcm from 5300 to 5500 MPa. It has been shown that the mentioned parameters are attained due to the dispersion mechanism of reinforcement with transformations in the structure (a stable decrease in the average grain size of the carbide phase, the disappearance of pores in the location of the binding Co phase, the formation of inhibitor phase clusters at phase interfaces) and phase composition of the composites.