T. A. Sviridova

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.

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.

Ceramic-metallic (TiN-Cu) nanostructured ion-plasma vacuum-arc coatings for cutting hard-alloy tools

The structure and properties of TiN-Cu coatings with a broad range of copper concentrations (CCu = 0.6–20 at %), which were fabricated by the ion-plasma vacuum-arc deposition on a TT10K8B hard-alloy tool, including its cutting resistant tests, were investigated. The introduction of copper into the coating composition diminishes crystallites of the nitride phase from 100 to 20 nm. The hardness of coatings increases from 20 to 40 GPa, with an increase in CCu to 7–8%. The further increase in the copper content, which is accompanied by diminishing crystallites of the nitride phase, is characterized by a decrease in hardness to 14–15 GPa, which is associated with the influence of soft plastic metal. Resistant cutting tests of steel 35KhGSA of removable multifaceted plates (RMP) with the TiN-Cu coatings indicate that the optimally selected composition (TiN-7-8 at % Cu) increases RMP resistance more than by a factor of 6 and 2.5 as compared with tools without the coating and with the TiN coating deposited according to the basic technology, respectively.

The powdered calcium hydride TiNi intermetallic compound

A complex investigation of physicochemical properties and structural components of the calcium hydride TiNi intermetallic compound is performed. Peculiarities of the influence of various consolidation types (hot isostatic pressing and hydrostatic pressing with subsequent sintering in vacuum) on the chemical and phase compositions of compacts from studied powders are investigated by optical and scanning electron microscopy, X-ray structural analysis, and analysis of gas-forming elements. It is established that vacuum sintering makes it possible to decrease contents of oxygen, nitrogen, and especially hydrogen.

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.

The growth, structure, and magnetic properties of thin epitaxial films of GdMnO3 multiferroics

Thin epitaxial gadolinium manganite (GdMnO3) films were manufactured on single-crystal substrates of neodymium gallate (001) (NdGaO3) and strontium titanate (001) (SrTiO3) by the high-frequency magnetron sputtering method. The RBS analysis demonstrated that the thickness of the obtained films was ∼100 nm and the chemical composition corresponded to the stated stoichiometry. It was established by the X-ray diffraction analysis of the structure and phase composition of the obtained films that all films were single-phase but, depending on the temperature of the substrate during sputtering they have one or several types of orientations relative to the substrate. The X-ray diffraction analysis and high-resolution electron microscopy data on gadolinium manganite films on neodymium gallate substrates were verified. Features pointing to phase transitions in GdMnO3 that were earlier discovered on bulk single-crystal samples were found in the temperature dependence of the magnetic susceptibility.

Calcium hydride synthesis of Ti–Nb-based alloy powders

The metallothermic (calcium hydride) synthesis of Ti–Nb alloy powders alloyed with tantalum and zirconium is experimentally studied under various conditions. Chemical, X-ray diffraction, and metallographic analyses of the synthesized products show that initial oxides are completely reduced and a homogeneous β-Ti-based alloy powder forms under the optimum synthesis conditions at a temperature of 1200°C. At a lower synthesis temperature, the end products have a high oxygen content. The experimental results are used to plot the thermokinetic dependences o formation of a bcc solid solution at various times of isothermal holding of Ti–22Nb–6Ta and Ti–22Nb–6Zr (at %) alloys. The physicochemical and technological properties of the Ti–22Nb–6Ta and Ti–22Nb–6Zr alloy powders synthesized by calcium hydride reduction under the optimum conditions are determined.

Formation of protective coatings on steel Kh12MF by the force of the sequential electric spark treatment by boride and carbon-containing electrodes

Coatings on steel Kh12MF are fabricated by the force of electric-spark treatment by the TiB2-20% NiAl electrode and carbon-containing materials. Kinetics of their formation, the phase composition, mechanical and tribological properties, roughness, and durability to high-temperature oxidation are investigated. When depositing the coating using the TiB2-20% NiAl electrode, the effect of a disproportionate increase in the substrate erosion, which is observed with an increase in the energy of a single pulse and leads to lowering the content of boride phases in the coating is discovered. The subsequent electric-spark treatment of the boride coating using an electrode made of fine-grain dense graphite led to a noticeable improvement of tribological properties of the coating having no noticeable effect on its durability to high-temperature oxidation. In the case of applying an electrode made of the silicicated composition material, the coating durability to high-temperature oxidation increased substantially, but no improvement of tribological properties was observed.