The strength of experimental samples of SiC/SiC composite pipes is studied during axial and ring tension under normal conditions. The samples are fabricated from a three-dimensional Hi-Nicalon Type S wicker fiber frame with an interphase pyrocarbon layer and a SiC matrix produced by PIP and CVD. The fracture mechanism of the SiC/SiC composite is found to be quasi-plastic. The strength during axial and ring tension is 283 and 244 MPa, respectively.
The defects and structure of the oxide films formed by the oxidation of tubular samples of E110 and E635 zirconium alloys in water and water with the addition of lithium are investigated. The crack sizes in the films before and after compression loading are quantitatively analyzed, and the kinetics of crack accumulation in the oxide films and the character of their fracture are analyzed. The initial defects are shown not to affect the fracture of the E635 alloy films during loading; however, along with a structure, they determine the fracture of the E110 alloy films.
Abstract—A finite element simulation of the state of stress in the femur–condylar prosthesis biotechnical system is performed, and its mechanical behavior is analyzed. The metallic components of the endoprosthesis (implant) are made of a VT6 titanium alloy, and the plateau of the tibial component is made of ultrahigh-molecular-weight polyethylene. The stresses in the bone structures and the most severely loaded components of the endoprosthesis are calculated at a functional load of 3300 N. A high degree of similarity of the biomechanical behavior of the biotechnical system (with the endoprosthesis) to the behavior of a healthy femur has been established. The stresses and strains of all components of the biotechnical system are shown not to exceed their critical values. The calculation results made it possible to predict the operational capability and reliability of the endoprosthesis components under static and cyclic loads, the wear resistance of the mobility unit, and the reliability of the cement mantle.
The mineral and chemical compositions of the kaolin clay from the Suvorovskoe deposit are studied by X-ray diffraction and inductively coupled plasma atomic emission spectrometry. The conditions of the thermal calcination and decomposition of the kaolin clay with sulfuric and hydrochloric acids are optimized: the calcination temperature and time are 650–700°C and 60–90 min, respectively. The degree of extraction of Al2O3 from the calcined clay to sulfuric acid solutions is 92–94%, and that to hydrochloric acid solutions is 76–78%. The influence of different flocculants on the separation of liquid and solid phases is studied. The use of polyacrylamide is shown to increase the filtration rate by a factor of 1.5–2. The coagulation properties of aluminum sulfate and hydroxochlorides, namely, oxidizability, chromaticity, and concentrations of aluminum and iron in the treated water, are studied. The tested coagulants can efficiently be applied for the treatment of drinking and sewage waters at low and high temperatures in a wide pH range of the waters to be treated.
Low-temperature synthesis of ceramics and cemented carbides based on plasma-chemical tungsten and titanium carbides nanopowders and micron-sized commercial titanium carbide powders has been investigated. Compact samples were prepared by spark plasma sintering (SPS), which consists in high-speed heating of powders at a rate of 50°C/min in vacuum under pressure up to 70 MPa. Compact samples with high density were obtained in a narrow temperature region above 1000. Phase evolution of double carbide having FCC lattice is considered based upon XRD data. A model for calculating the theoretical density of this phase is proposed, the calculated values agree with the experimental data.
The theories and mechanisms that explain the processes of modification of primary silicon in hypereutectic silumins are considered. The solidification of a hypereutectic silumin containing a rare earth element (REE), namely, yttrium, ytterbium, samarium, erbium, lanthanum, or neodymium, is studied. The phase transformation temperatures and the parameters that take into account the precipitation of a solid phase in the solidification temperature range are determined. Differences in the solidification parameters and the character of solid-phase precipitation in alloys modified by yttrium, ytterbium, samarium, erbium, cerium, or neodymium are revealed. Further investigations should be performed to clarify the mechanism of the REM modification of primary silicon in hypereutectic silumins.
The conductometric method is used to study the dependences of the electrical conductivity (EC) of aqueous solutions of ammonium carbonate and solutions of the ammonium carbonate–ammonium perrhenate system on the reagent content in the concentration range 0.1–1.8 mol/L for (NH4)2CO3 and 0.01–0.1 mol/L for NH4ReO4 and on the solution temperature in the range 20–50°C. EC is found to increase linearly with the electrolyte temperature and nonlinearly with the reagent concentration. The temperature coefficients of EC and its activation energies are calculated in the concentration and temperature ranges under study. The EC activation energy is found to decrease as the solution temperature increases. The calculated EC activation energies indicate a diffusion character of charge transfer.
The relaxation resistance and corrosion resistance of ultrafine-grained (UFG) steel 08Kh18N10T samples fabricated by equal-channel angular pressing (ECAP) at temperatures of 150 and 450°C are investigated. The UFG steel has a high macroelasticity limit and yield strength and exhibits a decrease in the Hall–Petch coefficient due to the fragmentation of δ-ferrite particles during ECAP. UFG steel samples are found to have 2–3 times higher relaxation resistance as compared to coarse-grained steel samples. ECAP is shown to increase the rate of general corrosion. Despite a decrease in the corrosion resistance, the UFG steel samples have high intergranular corrosion resistance. The decrease in the corrosion resistance of the UFG steel is found to be caused by an increase in the volume fraction of strain-induced martensite during ECAP.
The microstructure and microhardness of 316L-type austenitic stainless steel obtained by selective laser melting and then annealed at 900–1200°C have been studied. This paper is aimed at clarifying the features of the recovery process in the steel. The experimental samples were developed by selective laser melting using a ProX200 3D system in a nitrogen atmosphere without platform preheating. The laser power of 240 W, the beam speed of 1070 mm/s, the distance between tracks of 80 μm, and the layer thickness of 30 μm were applied. Annealing was carried out at temperatures of 900–1200°C for 1 h and at temperatures of 1000 and 1100°C for 1 to 10 h. It was found that the recovery processes at temperatures of 900–1100°C developed with a very sluggish kinetics. After 1 h annealing at 900–1100°C, the steel microstructure steel was characterized by a grain size of 25 ± 1 µm, and a dislocation density of 8.7 × 1013 m–2. An increase in the annealing duration to 10 h did not lead to significant changes in the microstructure of the steel samples annealed at 1000°C, whereas the samples annealed at 1100°C experienced the developmen of primary recrystallization resulting in twofold decrease in the dislocation density. The development of recovery in the present steel during annealing at temperatures of 900–1100°C could be expressed by Arrhenius-type relationship with a quite low activation energy of about 10 kJ/mol.
The extraction properties of a series of diamides of 2,2-bipyridine-6,6-dicarboxylic acids with respect to americium, curium, neptunium, thorium, light lanthanides and a series of d-elements present in solutions of highly radioactive wastes have been studied in this work. It has been shown that the extraction properties of diamides are determined not only by the structure of the heterocyclic framework, but also by the nature of substituents in positions remote from oxygen centers. The influence of substituents in a series of extractants is determined by differences in their electronic nature, and also depends on their volume and position. In the work, effective and selective extractants were found for the separation of the Am/Eu pair (SF up to 27), and fundamental patterns were revealed between the structure of the extractant and the efficiency of extracting metal ions.
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