Yu. S. Pogozhev

Self-propagating high-temperature synthesis of composite targets based on titanium carbonitride, silicide, and aluminide for ion-plasma deposition of multifunctional coatings

The macrokinetic features of combustion of the mixtures in the Ti-Al-Si3N4-C system calculated for the formation of compact ceramic materials (CCMs), the composition of which is described by the general formula X(TiAl3) + (100 − X)(0.448TiC0.5 + 0.552(Ti5Si3 + 4AlN) with mixture parameter X = 10–50%, are investigated. Compact CCM samples with the main structural components in the form of TiCxNy grains and binding phases TiAl3 and Ti5Si3 are fabricated by the technology of forced self-propagating high-temperature synthesis (SHS) compaction. An increase in X promotes the formation of the Mn+1AXn phase with the composition Ti3SiC2 in the synthesis products. Complex investigations into the physicomechanical properties of the obtained ceramics are performed. Based on their results, the inverse dependence of the density and hardness of compact materials on parameter X is established. Tests of the samples for oxidation resistance showed that the obtained CCMs based on titanium carbonitride, silicide, and aluminide possess excellent resistance to high-temperature oxidation, and their oxidation rate in air at t = 900°C for 30 h does not exceed 7.8 × 10−5 g/(m2 s).

Silicon carbide ceramics SHS-produced from mechanoactivated Si–C–B mixtures

We investigated the influence of mechanical activation (MA) and initial temperature T0 on combustion temperature Tc and burning velocity Uc for 90% (Si + C)–10% (4B + C) mixtures as well as on product morphology. Mechanical activation was found to strongly change the size and morphology of Si and graphite particles (by a factor of 6–8), lead to accumulation of micro strains, and increase the reactivity of green mixture. An increase in T0 was found to proportionally increase the values of Tc and Uc but produce little or no influence on the phase composition of product. The SiC powder consisting of 50–100 nm crystallites was obtained by diminution of combustion product and then used to prepare, by hot pressing, a ceramic PVD target for magnetron sputtering.

Fabrication of cast electrodes from nanomodified nickel aluminide-based high-boron alloy to fabricate spherical powders using the plasma rotating electrode process

A complex manufacturing method of billets from material based on high-boron nickel aluminide is proposed. The method includes manufacturing the semifinished alloy products using a combined method of self-propagating high-temperature synthesis and centrifugal casting from oxide feedstock and subsequent vacuum induction remelting with the introduction of Al-based foundry alloys containing nanosized ZrO2 and modifying the structure. The evolution of the microstructure and phase composition is investigated at all production stages. A cast ZrO2-modified cylindrical billet, which possess high purity in regards to gas impurities (O 0.005 wt % and N 0.0001 wt %) and is suitable for the further production of powders by the plasma rotating electrode process, is fabricated according to the proposed technology.

Cast NiAl/Ni20Al3B6 composites by centrifugal SHS

Cast NiAl/Ni20Al3B6 composites containing 2.3–3.5 wt % B have been prepared by centrifugal SHS for the first time. The composite materials comprised of a solid-solution matrix based on NiAl with inclusions of Ni20Al3B6 and complex boride (Mo, Cr)B. Best results were achieved at centrifugal accelerations 150–200 g in open air. Cast materials based on NiAl and τ-borides seem promising for use in turbine power units.

FEATURES OF PRODUCTION AND HIGH-TEMPERATURE OXIDATION OF SHS-CERAMICS BASED ON ZIRCONIUM BORIDE AND ZIRCONIUM SILICIDE

The paper is dedicated to the study of kinetics and combustion mechanism of reaction mixtures in Zr–Si–B and Zr–B systems, production of compact ceramic materials in a process of SHS compaction, as well as studying their heat resistance. The paper demonstrates that temperature and combustion speed dependencies of compounds in the Zr–Si–B system on the initial temperature (T 0 ) are linear, i.e. with a rise in T 0 , staging of chemical reactions of zirconium diboride and disilicide formation does not change. The paper calculates values of the effective SHS process activation energy, which demonstrate the crucial role of the reaction interaction between zirconium and boron and silicon in a melt. The paper studies the staging of chemical reactions in a mixture Zr–Si–B combustion wave: initially, the ZrB 2 phase is formed from the melt by crystallization, then the ZrSi 2 phase appears with a delay of 0,5 s and 1 second later unreacted Si crystallizes. The paper studies the phase composition of synthesis products with diboride ZrB 2 as a main component and zirconium disilicide ZrSi 2 , Si and boride ZrB 12 depending on the initial reaction charge composition. The new compact samples characterized by high hardness and low residual porosity were produced in the process of power SHS compaction. Formation of oxide films SiO 2 –ZrO 2 –B 2 O 3 along with the complex oxide ZrSiO 4 , which serve as an effective diffusion barrier and reduce the oxidation rate, occurs on the surface of SHS-samples in response to their high-temperature oxidation and depending on their composition.

Synthesis of high-temperature Mo5SiB2-based ceramics in the combustion mode

This study is devoted to the synthesis and investigation of the Mo5SiB2-based ceramic material (T2 phase). The influence of the initial temperature on basic combustion parameters is shown. It is found that preheating the reaction mixture enables the initiation of the combustion in the self-oscillatory mode and the initial temperature dependences of the combustion temperature and rate have a linear character. The effective activation energy of the SHS process is calculated. Some variants of chemical reactions between Mo, Si, and B are proposed to explain the combustion mechanism in the investigated ternary system. Compacted samples are obtained using the forced SHS compaction. The phase composition, structure, and properties of synthesized ceramic materials, in which Mo5SiB2 grains are the main component with an average size of 10–20 μm, are studied. The lines of Mo3Si and Mo intermediate phases, the total fraction of which does not exceed 4%, are identified as well. The produced T2 phase-based material has a high specific density and hardness.

The influence of elemental composition and surface topography on adhesion, proliferation and differentiation of osteoblasts

The influence of elemental composition and surface topography of substrates on the adhesion, proliferation and early differentiation stages of mouse osteoblasts, line MC3T3-E1, cultured on the surface of titanium and multicomponent bioactive nanostructured films (MuBiNaFs) Ti-Ca-(P)-C-O-N and Ti-Ca-Si-C-O-N has been studied. Osteoblasts spread both on the surface of uncoated titanium samples and on the samples coated with the films and had more elongated and irregular shape than the cells cultured on control glass substrate. Immunofluorescence study has shown that osteoblasts formed straight actin bundles associated with focal contacts. Osteoblasts on titanium films formed fewer focal contacts than the cells cultured on Ti-Ca-(P)-C-O-N films. The sandblast treatment did not affect the distribution of the focal contacts and actin structures within the cells. Osteoblasts actively divided on the surface of Ti-Ca-(P)-C-O-N and Ti-Ca-Si-C-O-N films and alteration of surface topography did not affect their growth rate. The quantitative colorimetrical test on alkaline phosphatase activity has shown that modification of surface topography does not affect the level of osteoblastic differentiation. Thus, the elemental composition plays an important role in the interaction of osteoblasts with the surface of films, while the modification of the surface topography in the range of Sq from 0.4 to 1 μm does not influence adhesion, proliferation, and differentiation of osteoblasts.

Production of a sintered alloy based on the TiAl intermetallic compound: Part 2. Investigation into forming and sintering processes

A complex production technology of electrodes from the powder alloy based on titanium aluminide TiAl, which includes the stages of fabrication of the powder alloy by calcium hydride reduction, treatment of the powder in a ball hard alloy mill with the addition of Y2O3 as a structural modifier, and the hydrostatic formation and sintering of a billet, is proposed. Formation and sintering processes are investigated for experimental samples and the alloy microstructure is investigated at all stages of process flowchart. The electrode for the plasma centrifugal spraying of the granules is fabricated using this technology.

NiAl-based electrodes by combined use of centrifugal SHS and induction remelting

NiAl-based electrodes of a required size were fabricated by combined use of centrifugal SHS casting and induction remelting in an inert atmosphere and characterized by modern analytical methods. Thus produced electrode materials exhibiting high chemical purity and low content of impurity gases (0.005 wt % O, 0.0001 wt % N) can be recommended for use in centrifugal plasma sputtering of micro granules via the plasma rotating electrode process (PREP).

Production of a sintered alloy based on the TiAl intermetallic compound. Part 1: Calcium-hydride fabrication technology of the Ti–47Al–2Nb–2Cr powder alloy and its properties

Alloy powder of the Ti–47Al–2Nb–2Cr composition (at %) with a structure of TiAl (60 wt %) and Ti3Al (40 wt %) is prepared by the calcium-hydride method. The mode of calcium-hydride synthesis is optimized for the Ti–50Al (at %) model alloy. It is established that the reduction temperature should be no lower than 1100°C, while the excess of the CaH2 reducing agent should be no lower than 15 wt %. The main physicochemical and manufacturing properties of the synthesized Ti–47Al–2Nb–2Cr powder alloy, which provide the formation of dense compact items during its subsequent consolidation processes, are determined using modern analytical methods.