Search

The elastic (Young's modulus) and relaxation (amplitude-independent internal friction) properties of metallic V and its low-activated alloys (V–4Cr–4Ti, V–W–Cr, V–Ta–Cr–Zr) have been studied by dynamic mechanical spectroscopy in the low-frequency range (0.5–30.0 Hz) and in the temperature range of 25–400°C in their annealed states. The solid-solution concentrations and diffusion characteristics (diffusion activation energies) of the C, O, N interstitial atoms have been determined. The changes in the obtained characteristics in comparison with their values for the cold-deformed states of the investigated materials have been determined. [ABSTRACT FROM AUTHOR]

The results of investigations of the effect of thermomechanical treatment (TMT) regimes on the regularities of phase transformations, microstructure, and mechanical properties of low-activation alloys of the V–4Ti–4Cr–(C, O, N) system are summarized. The mechanisms of these transformations and the relationship between the microstructure and the level of strength and plasticity are established. The TMT regimes are presented that provide a uniform bulk distribution of nanosized particles of stable oxycarbonitride, a significant increase in their density (dispersion), and an increase in the thermal stability of the microstructure. It is shown that these regimes lead to a significant (by 30–60%) increase in the short-term strength of alloys in a wide (from 293 to 1073 K) temperature range with preservation of a sufficiently high plasticity. [ABSTRACT FROM AUTHOR]

The elastic (Young's moduli) and relaxation (amplitude-independent internal friction) properties of ferritic-martensitic 12% chromium steels EK-181 (low-activated) and EP-823 depending on their heat treatment modes (THT—traditional, CHT—combined) have been investigated by the method of dynamic mechanical spectroscopy in the low-frequency range (0.5–30.0 Hz) and the temperature range of 25–400°С. The temperature, frequency, and amplitude dependences of Young's moduli and internal friction have been determined. Frequency and amplitude independence of elastic moduli is observed. The values of Young's moduli depend on their modes of heat treatment of steels (THT, CHT) and for EK-181 steel is always higher than for EP-823 steel. The temperature dependences (spectra) of internal friction in steels for different modes of their heat treatment and at different frequencies almost monotonically increase with increasing temperature. Relaxation peaks are practically absent (within the measurement accuracy), which determines the practical absence of solid interstitial solutions (C, O, N) in the studied steels. [ABSTRACT FROM AUTHOR]

The effect of high-temperature thermomechanical treatment (HTMT) with deformation in the austenitic region on the regularities of low-temperature embrittlement of low-activation 12% chromium ferritic-martensitic steel EK-181 is investigated in comparison with traditional heat treatment (THT) during dynamic tests on impact toughness and static tests on uniaxial tension in the range from −196 to 20°C. It is found out that HTMT increases both the tensile strength properties of steel and its impact toughness. At the same time, the temperature of its ductile-brittle transition does not practically change relative to the THT. It is observed that the features of steel microstructure after HTMT, the formation of delaminations (during fracture of Charpy-type specimens) in the planes parallel to the plane of hot rolling, have a positive effect on its impact toughness. [ABSTRACT FROM AUTHOR]

The elastic (Young's) modulus and relaxation properties (amplitude-independent internal friction) of bcc metals and alloys (vanadium, V–4Cr–4Ti, V–W–Cr, and V–Ta–Cr—Zr alloys) have been studied in the temperature range of 25–400°С by means of dynamic mechanical spectroscopy within a low-frequency range (0.5–30.0 Hz). No carbon in vanadium and V–W–Cr alloy in solid-solution state is revealed. In the case of vanadium and V–W–Cr alloy, the solid-solution concentrations of oxygen and nitrogen and the diffusion characteristics thereof (diffusion activation energy, characteristic relaxation time, and the preexponential factor in the diffusion equation) have been determined. In the case of V–4Cr–4Ti alloy, carbon, oxygen, and nitrogen solid solutions have not been observed. In V–Ta–Cr–Zr alloy, the solid-solution concentrations of interstitial atoms (C, O, N) are substantially lower than those in vanadium and V–W–Cr alloy. The values of elastic modulus in vanadium alloys can be either higher or lower than the elastic modulus inherent in vanadium depending on type of alloy (alloying) and on temperature. The V–4Ti–4Cr alloy exhibits the smallest value of the elastic modulus among all the materials under study. The temperature curves of the elastic (Young's) modulus for the studied materials exhibit no features, except for a slight local relaxation of the Young's modulus in the case of vanadium and V–W–Cr alloy in the temperature range of the relaxation peaks. [ABSTRACT FROM AUTHOR]

Static and fatigue strength at room temperature under conditions of repeated stretching of lowactivated ferrite-martensite 12% chromium steels EK-181 (Fe-12Cr-2W-V-Ta heat treatment + aging in lead at 600°C, 3000 h), EP-823 (Fe-12Cr-W-V-Ni-Mo-Nb, annealed condition), and alloy V-4Ti-4Cr (heat treatment + aging in lead at 600°C, 3000 h) were studied. It was shown that for materials there is straight-line dependence between the level of rupture resistance values and fatigue strength. The maximum fatigue limit of 600 MPa appears in steel EK-181 after a standard heat treatment and aging in lead at 600°C, 3000 h, and the minimal one of 300 MPa is observed in vanadium and V-4Ti-4Cr alloys. The fatigue failure mechanism is predominately of ductile character for all materials studied. The fatigue cracking originates near the surface and in some cases clustering of nonmetallic inclusions is the place of origin. The fatigue crack propagation is related to formation of a typical striation relief. Significant distinctions in the fracture surface relief of specimens after standard heat treatment and aging in liquid lead are not observed. [ABSTRACT FROM AUTHOR]

The effect of low-temperature damaging irradiation on the high-temperature embrittlement (cold shortness) in metals was investigated in a previously proposed model. The cold shortness state with possible brittle fracture in metals is not formed in the irradiation process because of the dynamical radiation processes arising. [ABSTRACT FROM AUTHOR]

The dislocation mechanisms of formation of the ductile-brittle transition temperature and the low-temperature brittle fracture of metals (single crystals, polycrystals) with various crystal lattices (bcc, fcc, hcp) are considered. The conditions of appearance of cold shortness and intracrystalline crack propagation (brittle fracture) are determined. These conditions can be met in bcc and some hcp metals and cannot be met in fcc and many hcp metals. The nondestructive internal friction (at 100 kHz) method is used to determine the temperature ranges of cold shortness (ductile-brittle transition temperatures) in bcc metals (ferritic-martensitic EK-181 steel, V-4Ti-4Cr alloy), which depend on their structure-phase state and strength (yield strength). [ABSTRACT FROM AUTHOR]

Shock fracture mechanisms of different scales were investigated on epoxy composite materials reinforced with silicon carbide microparticles of different concentrations. It is shown that the high heterogeneity of the epoxy composites at different structural scales is one of the factors responsible for their physical and mechanical properties. Under dynamic loading, the material reveals a developed structural scale hierarchy which provides self-consistent deformation and fracture of the material bulk with the lead of rotational deformation modes. As a result, microcracks develop due to low shear strain limited in addition by reinforcing particles. At the start of a main crack, microscale mechanisms dominate, whereas the propagation of its front is governed by macroscale fracture mechanisms. [ABSTRACT FROM AUTHOR]

We investigate formation of pores in the process of formation of the epoxy matrix-polyvinyl alcohol-disperse filler system and their influence on the impact toughness. The optimal ratio of the components for the preparation of a material with given properties is determined. [ABSTRACT FROM AUTHOR]

Our laboratory has demonstrated that treatment of MCF-7 breast cancer cells with melatonin (Mlt) followed 24 h later with physiological concentrations of all-trans retinoic acid ( atRA) results in apoptosis. These studies were extended into trials using the N-nitroso-N-methylurea (NMU)-induced rat mammary tumor model. Initial studies conducted by feeding the animals 9-cis-retinoic acid ( 9cRA in the chow) and administering melatonin by subcutaneous injection in the late afternoon demonstrated that the combination of Mlt and 9cRA was able to significantly prevent tumor development, and that the combination was more efficacious that either Mlt or 9cRA alone. In this report, we conducted studies to determine if lower doses of 9cRA could be used in combination with Mlt while still maintaining anti-tumor activity and if the route of administration of 9cRA (bolus (gavage) v.s. chronic (chow) routes) affected its interaction with Mlt. The studies presented here demonstrate that significantly reduced doses of 9cRA can be used in combination with Mlt while maintaining anti-tumor efficacy. Furthermore, our studies demonstrate that 9cRA is equally effective when it is administered chronically (chow) or as a bolus (gavage). These data demonstrate that the combined use of Mlt and 9cRA produces additive or synergistic effects, which are more efficacious than 9cRA alone. This combination of Mlt and 9cRA could be a potentially useful clinical treatment regimen for breast cancer since it allows the use of lower doses of retinoic acid, thus, avoiding the toxic side effects associated with the use of high dose retinoids. [ABSTRACT FROM AUTHOR]

The structure and thermophysical properties of fullerene C60aqueous solutions were investigated both experimentally and theoretically. The aggregation kinetics results indicated that the structure of fullerene C60aggregates in water could be described as a fractal system. The IR and electronic absorption spectra obtained confirm the presence of the crystalline phase in aqueous solution. The numerical values of thermodynamic coefficients αP, βT, βS, cP, and cV, and sound velocity were determined from the measured ( P– V– T) data. The vibrational spectrum of the crystalline structure (Thsymmetry group) formed from the hydrated single fullerene C60molecules in aqueous solutions was calculated using the molecular dynamics approach. [ABSTRACT FROM AUTHOR]