Volume 7, Nº 4 (2016)

The effects of interaction between the intermetallic γ’ phase and matrix γ phase based on a nickel solid solution with acidic and alkaline electrolytes at room and high temperatures are studied by high-resolution metallographic techniques using scanning electron microscopy, local energy-dispersive X-ray spectroscopy, and wavelength dispersive X-ray fluorescence spectroscopy. Defects formed on the surface of casts of turbine blades are considered, and recommendations to redress them are provided.

The structure and transport and diffusion properties of film matrices based on polyamide and polyhydroxybutyrate blends obtained from solutions and melts are studied. Quantitative analysis of the diffusion and sorption of water shows that the dependence of the diffusion mobility of water increases exponentially with increasing content of polyamide as the more hydrophilic component of the system. The developed materials are recommended for the creation of new therapeutic systems of controlled release of drugs.

At present, different powder materials are produced and powder products of different composition are manufactured. The most widespread are iron powder materials used in mechanical engineering. These materials are characterized by high strength combined with a high level of ductility and toughness and low tendency to brittle fracture. The properties of these materials are mainly determined by the structure formed by sintering as a result of counterdiffusion and interaction of the initial components. Upon sintering, a heterogeneous and porous structure is formed. The effect of porosity and the interpore distance on the fracture toughness is analyzed. The results of the tests prove to be consistent with the phonon theory of discrete fracture.

The influence of the size and number of calcium carbonate granules introduced to the cement matrix of an alpha-tribasic calcium phosphate–orthophosphoric acid solution on the compression strength of the composite material was studied. A potential increase in strength by a factor of six by the introduction of an optimal amount of granules into the matrix was determined.

The phase transformations in carbon doped tungsten silicides are studied. In the eutectic alloys of tungsten silicides depending on the level of doping with carbon, SiC is present in the structure immediately after quenching or only after additional annealing (aging). The effect of the silicon content in the alloy on the type of formed carbides is detected. The possible features of the W–Si–C phase diagram are discussed.

Aluminum oxynitride Al₂₃O₂₇N₅ was synthesized by solid phase synthesis from a stoichiometric mixture of aluminum nitride and aluminum hydroxide at 1850°C in a nitrogen atmosphere. Aluminum oxynitride ceramic was prepared from the synthesized powders by hot pressing without sintering additives. The obtained samples were characterized by scanning electron microscopy and X-ray phase analysis; the mechanical properties of the ceramic samples were measured.

This work investigates the fracture mechanisms upon static tension of flat specimens of structural steels of Russian grade 09G2 and steel of Russian grade K3, which are widely applied in the oil and gas industry, in the defect-free state and after growing of an artificial defect in the form of a fatigue crack using an SDS1008 acoustic emission diagnostic system and fractographic analysis of fracture surface.

We developed a process of plasma wire spraying of three-dimensional capillary porous titanium coatings for intraosteal implants with the use of two additional arc discharges between the plasma gun and the wire and between the plasma gun and the substrate. By raising the temperature of sprayed particles and activating the substrate, we enhanced the shear strength up to 120 MPa for a titanium coating having the porosity of 46%.

The paper proposes a design concept of multifunctional layered composite materials, i.e., sandwich panels, intended for use in equipment and facilities operating in Arctic conditions. A general layout of the composite structural elements is proposed, a selection of the components is discussed, and fire-resistant and standard sandwich panels are considered.

This article discusses the physical and mechanical properties of Fe–Cr–1%V alloys as a function of Cr content in the range of 12–16% and of annealing temperature. Structural parameters and processes generating alloy properties are analyzed.

Research results of the corrosion resistance of 30XGCN2A steel after irradiation by a polyion beam using an implanter of copper, lead, monotectic alloy of 64% Cu–36% Pb (MA), and MA + Sn and MA + Al alloys as a cathode are given. An increase in the corrosion resistance of implanted samples during a total corrosion test carried out in a salt-spray chamber, as well as an increase in the electrode potential threshold value of the pitting corrosion when using an implanter of MA + Sn and MA + Al alloys as a cathode, is observed.

The influence of calcium microalloying on the homogenization temperature of ingots of AV grade alloys of the Al–Mg–Si–Cu system is studied. It is shown that, to provide the maximum dissolution of excess phases, the homogenization temperature of ingots should be chosen in a range of 560–575°C. The microstructure of ingots of the calcium-doped AV alloy has two types of phase components over boundaries of dendrite cells: light skeleton-like and dark compact round shapes. The calcium microalloying additive results in the formation of dispersed particles of excess intermetallide phases in the AV alloy with variable composition of Al_xSi_yCa and Al_xSi_yMg_zCa, which promote nucleation of new grains. It is likely that calcium as the surfaceactive element changes the contribution of grain-boundary energy. This is the constraint for collective recrystallization.

The paper discusses the relationship between the reflection of microwave electromagnetic radiation and the composition of a composite multilayer material made from rubber filled with carbonyl iron particles and nonwoven fabric reinforced with carbon fiber. It is found that the radio absorbing composite material has low reflectivity at electromagnetic wave frequencies less than 4 GHz. It is shown that the composite material has the highest absorption capacity when electromagnetic waves are incident on the nonwoven fabric layer of the material.

This article describes a procedure for calculation and construction of the yield point as a function of average particle size of the Ni₃Al phase at 750, 850, and 950°C. The developed approach can be applied to thermally hardenable alloys and is related to nucleation of intermetallic phases. This procedure of calculation and analysis of dispersion hardening facilitates selection of optimum modes of thermal treatment aimed at production of preset particle size of phases, determining maximum hardening of aging alloys.

In this work, the deposition conditions and phase composition of a carbonitrided coating on a complex alloyed hot-work 25Kh3M3NBTsA structural steel are studied using thermodynamic modeling and structural methods. It is shown that the main phases of the surface layers of carbonitrided steel are the solution of nitrogen and carbon in α-Fe, carbonitride, iron nitrides, and chromium and iron carbides. According to the results of thermodynamic analysis, carbide precipitate based on the Fe₃C phase and CrN-based nitride precipitate can be formed. The possible reasons for the absence of the CrN phase in experimental data are indicated. It is shown that the wear rate of carbonitrided coatings is determined by the microhardness of the carbonitrided layer, whereas the fatigue life is related to the crack propagation rate.

Composites in the MoSi₂ + Si₃N₄ system containing 1.0, 2.5, and 5.0 wt % Si₃N₄ were synthesized by hot pressing at the temperature of 1650°C and the pressure of 30 MPa. Silicon nitride powders of two types of were used as reinforcing additives: one with isometric equiaxed crystals and one with fibrous structure. The samples were characterized by microstructural and phase analyses; the relative density and the flexural strength were determined. Composites with the flexural strength of up to 410 MPa were synthesized. The resistance to low-temperature oxidation of MoSi₂ + Si₃N₄ composites in air at the temperature of 750°C was studied. The increase in the resistance to oxidation of composites with silicon nitride in air compared to pure molybdenum disilicide for both types of silicon nitride powders was established. For all the composites obtained, the parabolic oxidation rate constants were calculated.

A microporous ceramic with a pore size ranging from 1 to 6 μm and a relative density up to 56% was obtained from the calcium phosphate powder synthesized from aqueous solutions of monocalcium saccharate (CaC₁₂H₂₂O₁₁) and ammonium hydrophosphate. The composition of the synthesized nanosized powder is found to include hydroxyapatite and sucrose. The phase composition of the ceramic after calcination in the range from 900 to 1200°C is represented by β-tricalcium phosphate and hydroxyapatite. The resulting ceramic material can be recommended for the manufacture of bone implants.