V. B. Sverdun

Synthesis of ternary compounds of the Ti-Al-C system at high pressures and temperatures

Ternary carbides have been synthesized from a mixture of Ti, Al, and C powders taken in the stoichiometric relation 3/1.2/2 under quasihydrostatic pressures and temperatures. The amount of the MAX phase in samples and the material density has been increased by the two-stage synthesis at high pressures (1–2 GPa) and temperatures followed by homogenizing. The material, which had been produced at a pressure of 2 GPa, a temperature of 1200°C and annealed in an argon atmosphere, contained 94.3 Ti3AlC2-4.3 TiC-1.4 Al2O3 wt %. The material density and Vickers microhardness at the load of 4.9 N have been measured to be 4.27 g/cm3 and 3.3 GPa, respectively.

The effect of size of the SiC inclusions in the AlN–SiC composite structure on its electrophysical properties

AlN–SiC–Y3Al5O12 composite materials with a high absorption of microwave frequency (27–65 dB/cm) produced by pressureless sintering of mixtures consisting of AlN(2H), Y2O3, and SiC (6H) in 46, 4, 50 wt %, respectively, have been studied. The SiC components of the mixtures were used in sizes of 1, 5, and 50 μm. It has been shown that the resistivity of the developed materials depends essentially on the materials structures: sizes of SiC inclusions, distances between them, and state of the interfaces. It has been found that the increase of the SiC inclusions sizes in the material structure from 3 to 7 μm results in the decrease of the resistivity from 104 to 90 Ω·m, and at the decrease of the SiC inclusions sizes from 3 to 0.5 μm there forms a SiC uninterrupted skeleton, which also decreases the resistivity to 210 Ω·m. Thus, composite materials that contain 50 wt % SiC (inclusions sizes of 3 μm) are the most efficient in producing absorbers of microwave radiation. Interlayers of yttrium aluminum garnet, which are located at the SiC grains boundaries, prevent the forming of AlN(2H)–SiC(6H) solid solutions and thus, make it possible to keep high dielectric characteristics of a composite material based on aluminum nitride and afford a high absorption of a microwave radiation.

Thermal Stability and Mechanical Characteristics of Densified Ti3AlC2-Based Material

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 %.

Influence of oxygen and boron distribution on superconducting characteristics of nanostructural Mg-B-O ceramics

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.

Effect of the Additive of Y 2 O 3 on the Structure Formation and Properties of Composite Materials Based on AlN–SiC

The results of studies on the strength at bending and volumetric electrical resistance of composite materials based on AlN–SiC with additions from 2 to 6 wt % Y2O3. It is shown that at increasing the content of Y2O3 in the mixture from 2 to 6 wt % the compaction of the composites intensifies their electrical resistance from (1.4–5.4) × 106 to (1.8–5.94) × 107 Ohm·cm (at 20°C), which at the increasing temperature decreases exponentially and at 800°C for all composites is (5–6) × 104 Ohm·cm. It was determined that materials with the smaller content of Y2O3 have somewhat higher value of the ultimate strength during bending, namely, 110 MPa.

Presence of Oxygen in Ti-Al-C MAX Phases-Based Materials and their Stability in Oxidizing Environment at Elevated Temperatures

Presence of Oxygen in Ti–Al–C MAX Phases-Based Materials and their Stability in Oxidizing Environment at Elevated Temperatures T. Prikhnaa,∗, O. Ostash, V. Sverdun, M. Karpets, T. Zimych, A. Ivasyshin, T. Cabioc’h, P. Chartier, S. Dub, L. Javorska, V. Podgurska, P. Figel, J. Cyboroń, V. Moshchil, V. Kovylaev, S. Ponomaryov, V. Romaka , T. Serbenyuk and A. Starostina Institute for Superhard Materials of the National Academy of Sciences of Ukraine, 2 Avtozavodskaya Str., Kiev, 04074, Ukraine Karpenko Physical-Mechanical Institute of the National Academy of Sciences of Ukraine, 5, Naukova Str. Lviv, 79060, Ukraine Université de Poitiers, CNRS/Laboratoire PHYMAT, UMR 6630 CNRS Université de Poitiers SP2MI, BP 30179, F-86962 Chasseneuil Futuroscope Cedex, France The Institute of Advanced Manufacturing Technology, Wroclawska 37A, 30-011 Krakow, Poland EDL “Proton 21”, 48a, Chernovola Str., Kiev’s region 08132, Vishnevoe, Ukraine Lviv Polytechnic National University, 12 Bandera Str., Lviv, 79013, Ukraine

Erratum to: “structure and properties of superhard materials based on aluminum dodecaboride α-AlB12”

We would like to inform you that a sad mistake was made in one of our articles in “Journal of Superhaed Materials”, 2017, vol. 39, no. 5, pp. 299–307. The article is “Structure and Properties of Superhard Materials Based on Aluminum Dodecaboride α-AlB12” by T. A. Prikhna, P. P. Barvitskyi, M. B. Karpets, V. B. Muratov, V. B. Sverdun, P. Khaber, V. V. Kartuzov, V. E. Moshchil’, S. N. Dub, M. G. Loshak, L. I. Aleksandrova,V. V. Kovylyaev, V. V. Garbuz, and A. A. Marchenko.Thus, the author’s name P. Khaber should be replaced by R. Haber.

Structure and properties of superhard materials based on aluminum dodecaboride α-AlB12

The structures and mechanical properties of materials based on α-AlB12 without additives and with additions of carbon and titanium carbide sintered under high (2 GPa) pressure and by hot pressing (30 MPa) in the contact with hexagonal BN. The light materials were obtained having high hardness, fracture toughness, ultimate strengths at bending, Rbm, and compression. The addition of 17 wt % C to α-AlB12 and sintering at 30 MPa makes possible to achieve fracture toughness KIc (49 N) = 5.9 ± 1.4 MPa·m0.5, hardness HV (49 N) = 23.6 ± 2.8 GPa, bending Rbm = 310 MPa and compression Rcs = 423 MPa strengths and specific weight was γ = 2.7 g/cm3. The addition of 20 wt % TiC to α-AlB12 and sintering at 30 MPa resulted in the formation of AlB12C2 and TiB2, increase of the hardness HV (49 N) = 28.9 ± 1.9 GPa, Rbm = 633 MPa, Rcs = 640 MPa and γ = 3.2 g/cm3, the KIc(49 N) = 5.2 ± 1.5 MPa·m0.5.

Formation regularities of structures of AlN-SiC-based ceramic materials

Composite materials based on AlN-SiC have been produced by the pressureless sintering. It has been established that in the formation of the AlN-SiC-Y3Al5O12 structure the yttrium-aluminum garnet locates along the boundaries of SiC and AlN grains, thus preventing the mutual dissolution of AlN-SiC. It has been found that the increase of the SiC amount from 20 to 50 wt % results in changes of the a and c parameters of the crystal lattice from 0.49821 to 0.49837 nm and from 0.5046 to 0.498 nm, respectively, and in increase of the composite absorbing ability from 8.8 to 31.4 dB/cm (at frequencies of 9.5–10.5 GHz).

Structure and properties of oxygen-containing thin films and bulk MgB2

A structural Auger spectroscopy study of MgB2 thin (~140 nm) oxygen-containing polycrystalline films produced by magnetron sputtering and 99% dense MgB2 bulks synthesized at 2 GPa allows us to conclude that jc of MgB2 depends to a high extent on the amount and distribution of oxygen in the material matrix. jc reached 7.8-2.7 MA/cm2 below 1T at 20 K in the films and 0.3-0.9 MA/cm2 (depending on the boron used) in the bulks. The higher jc in MgB2 thin films can be associated with finer oxygen-enriched Mg-B-O inclusions and their higher density in the film structure compared to the bulk. Calculations of the total electron density of states (DOS) in MgB2, MgB1.75O0.25, MgB1.5O0.5 and MgBO showed that all the compounds are conductors with metal-like behaviour. The DOS is even higher in MgB1.5O0 5 than in MgB2 and the binding energy is similar. So, the experimentally found presence of some dissolved oxygen in MgB2 does not contradict its high SC performance. The introduction of a high amount of oxygen into the MgB2 structure does not dramatically reduce the materials Tc and allows obtaining highjc as observed in our MgB2 films and bulks.