Steel clad NiAl rods were prepared by high-temperature gas extrusion (HTGE) of steel cartridges stuffed with reactive Ni-Al powder compacts upon variation in warmup temperature T-w (600-780 degrees C) and gas (Ar) pressure P (200-480 MPa). A largest amount of NiAl and Ni3Al intermetallics in rod core was obtained at T-w = 780 degrees C and P = 200 MPa. For T-w < 660 degrees C (m.p. of Al), the rod core was found to contain significant amounts of unreacted Al and Ni. A transition zone of Al-Fe intermetallics (10 um thick) was found only in the rod obtained at T-w = 780 degrees C and P = 200 MPa. The core material of such rods exhibited a largest mean value of hardness (1050 HV). It is suggested that the yield of target intermetallics can be improved by using charge compacts prepared from mechanically activated Ni-Al blends. Combined use of (a) in-situ synthesis of target product in a core and (b) extrusion of the entire fixture seem promising for fabrication of composite materials with unique properties.

Total energy ab-initio calculations for some SHS products were performed by DFT method using VASP program package. The results of calculations along with XRD results and crystallographic modeling were used to explain specific features of the composition/structure of selected SHS products.

SHS in 3Si–SiO2–nAdd mixtures, where Add = FeCl3⋅6H2O or Fe2(C2O4)3⋅5H2O and n = 0.015–0.09 М, under 10 MPa of nitrogen gas was studied by XRD, SEM/EDS, and chemical analysis. The addition of gasifying salts decreased combustion temperature and improved phase composition of combustion products. In case of FeCl3⋅6H2O and n = 0.09 М, total yield of silicon oxynitrides Si2N2.2O0.8 and Si2N2O attained a value of 94 wt %, due to the presence of added iron. Crystal structure of the earlier unknown Si2N2.2O0.8 phase detected in combustion products derived from 3Si–SiO2–nFeCl3⋅6H2O mixtures was established by XRD analysis and crystallographic modeling.

The structure and phase composition of a material obtained via SHS in the combustion of a 87% Ti + 13% B powder mixture with the addition of Si3N4 is under study. The phase formation mechanism in this system is discussed. It is established that the material contains 64% of the TiB phase with an orthorhombic structure and 36% of the solid boron solution in titanium ( $$\alpha$$ -Ti[B]). The boron content in $$\alpha$$ -Ti significantly exceeds its equilibrium content according to a state diagram. In the case of combustion of an 87% Ti + 13% B mixture with the addition of 5% Si3N4, the finite product contains TiB, $$\alpha$$ -Ti[B], TiB2, and Ti5Si3 phase. The TiB phase is present in the form of two modifications: orthorhombic and cubic. The completeness of a structural transition of the cubic modification of TiB into an orthorhombic one is determined by the cooling rate of a sample. It is assumed that the combustion of the mixture with the addition of Si3N4 forms the dispersed discharges of TiN, which are the crystallization centers of cubic TiB.

The composition and crystal structure of compounds produced by self-propagating high-temperature synthesis (SHS) from the 5Ta–2Ni–3Al (at %) powder mixture followed by vacuum remelting at 3000°C are studied. The SHS product contains the following phases: TaNiAl (Laves τ1 phase), NiAl, Ni2Al3, and Ta. Its microstructure includes Ta85Ni7Al8, Ta52Ni20Al28, and Ta53Ni25Al22 ternary phases according to elemental analysis data. Reflections belonging to no known ternary phases in the Ta–Ni–Al system under consideration are revealed in the X-ray diffraction pattern of the remelted material. Based on the homological approach, it is found that these reflections belong to three phases with the structural types W6Fe7 ($$R\bar {3}m$$), Ti2Ni ($$Fd\bar {3}m$$), and Ta3Al ($${{P{{4}_{2}}} \mathord{\left/ {\vphantom {{P{{4}_{2}}} {mnm}}} \right. \kern-0em} {mnm}}$$). They are identified as reflections of three compounds, Ta6.5Ni6.5, Ti2Ni, and Ta2.84Al0.91, with unit-cell parameters differing from these for the same compounds with the conservation of the structural type. An increase in the unit-cell parameters of all revealed phases is noted when compared with known binary intermetallic compounds. This can be associated with the presence of Al atoms in the crystal lattice from the Ta6.5Ni6.5 phase and Al and Ta atoms in the phase with the Ti2Ni structural type. Phases Ta6.5Ni6.5 and Ti2Ni phases are identified as Ta6Ni6Al and Ta2Ni0.5Al0.5 by X-ray structural analysis and crystal-chemical modeling, and their structural type, composition, and unit-cell parameters are determined. The structure and composition are refined by the full-profile analysis, and the unit-cell parameters of the phases and their quantitative ratio in the material are determined. The phase composition of the material is as follows, wt %: 47 Ta6Ni6Al, 16 Ta2Ni0.5Al0.5, and 37 Ta3Al.

— The composition and structure of a new compound, Ni 3.35 W 9.65 C 4 , have been determined by comparing X-ray powder diffraction, crystal-chemical modeling, and density functional quantum-chemical calculation (VASP program) results. The compound, in cast form, has been prepared by a self-propagating high-temperature synthesis metallurgy method via combustion of an exothermic WO 3 + NiO + Ca + Al + C mixture.

Nano- and microcrystalline ZrB2 powders have been studied by high-temperature X-ray diffraction in the temperature range 300–1400 K, and their unit-cell parameters have been measured as functions of temperature. The thermal expansion coefficient (TEC) of ZrB2 has been shown to be a linear function of temperature, and its thermal expansion has been shown to be anisotropic: in the temperature range 300–600 K, both the micro- and nanocrystalline ZrB2 powders have anisotropic thermal expansion, with αa < αc. Above 640 K, the a-axis TEC of ZrB2 exceeds its c-axis TEC. The thermal expansion of the nanocrystalline ZrB2 powder has been shown to be considerably smaller than that of the microcrystalline ZrB2. The anomalously small thermal expansion of the nanocrystalline ZrB2 is tentatively attributed to the effect of a boric anhydride layer on the surface of the nanoparticles.

Titanium diboride nanoparticles with diameter of 5–7 nm have been synthesized via the reaction of TiCl 4 with NaBH 4 in a NaCl‒KCl ionic melt in an autoclave reactor.

— It has been shown using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, and elemental analysis that phase-pure VB 2 with an average particle size in the range 20–35 nm can be prepared in the temperature range 595–930°C by reacting vanadium(III) chloride and sodium borohydride in the molar ratio 1 : 10 in an argon atmosphere for 14–28 h.

The stability of the kappa phase of compounds Me 3+ x W 10– x C 3+ y (Me = Fe, Co, Ni) is calculated using the density functional theory. Crystal structures with disordered positions are calculated using an additive approach. The crystal structure of the kappa phase is presented as the superposition of four structures: Me 3 W 10 C 4 (A), Me 3 W 10 C 3 (B), Me 4 W 9 C 4 (C), and Me 4 W 9 C 3 (D). The statistical disorder in the crystals is determined from the relative contributions of these structures. The contribution from each structure is estimated from the calculated enthalpies. The effect 3 d -block metal has on the stability of the kappa phase and the character of statistical disorder is studied using the proposed approach.

— The products of reaction between TiCl 4 and NaBH 4 in NaCl/KCl or KBr ionic melts at 973 and 1023 K under an argon pressure of 5 MPa have been characterized by various physicochemical analysis techniques. The results demonstrate that these conditions lead to the formation of TiB 2 nanoparticles with hexagonal symmetry (sp. gr. P 6/ mmm , AlB 2 structure) and lattice parameters a = 0.3022–0.3025 nm and с = 0.3214–0.3221 nm. The average diameters of the TiB 2 nanoparticles evaluated from electron microscopy, specific surface area, and X-ray diffraction (crystallite size) data for the two synthesis temperatures are ~10 and ~15, ~12 and ~17, and ~5 and ~10 nm, respectively.

Boron carbide crystals of various compositions were studied by X-ray powder diffraction in the temperature range of 25-700 degrees C. The formation of a metastable structure of boron carbide under the conditions of self-propagating high-temperature synthesis was detected. Its metastability manifested in a decrease of the unit cell volume after the first heating-cooling cycle. The cell volume change disappeared in all the subsequent heating-cooling cycles. For B12C3 crystals this effect did not occur. The metastability of boron carbide crystals was explained by the presence of C and/or B atoms in crystalline structure channels and their motion along the channels and up to position of structural vacancies under the temperature increasing.

The results of studying steel cladded intermetallic rods manufactured by means of high-temperature gas extrusion applied for the first time for reactive powder mixtures are presented. The tests were performed on the Ni–Al model system.