Influence Of Interstitial Impurities Research Articles

ВЛИЯНИЕ ПРИМЕСЕЙ ВНЕДРЕНИЯ В СПЛАВАХ МИШЕНЕЙ СИСТЕМЫ Zr–Y НА КАЧЕСТВО ТЕПЛОЗАЩИТНОГО КЕРАМИЧЕСКОГО ПОКРЫТИЯ

The influence of interstitial impurities in the Zr–Y target alloys (manufactured by two different techniques) on the quality of thermal barrier ceramic layers of heat resisting coating are studied in this work. The heat resisting ceramic coating manufactured in the UOKS-2 devices by magnetron medium-feculence plasma–chemical deposition on the surface of components that are used at the high temperatures (above 1150 °C). It was found that when the content of interstitial impurities in the target alloy is more than 0,1% (1000 ppm), the rate of the coating process decreases and has to be maintained by increasing the energy of argon ions. This leads to overheating of the target alloy and the surface of the parts (substrate) which impairs the adhesion of the deposited atoms.

Influence of Hydrogen and Carbon on the Atomic Ordering and Ultimate Strength of N36 Alloy

We study the influence of hydrogen on the parameters of atomic ordering (Kurnakov temperature T K and long-range atomic order η) in N36 alloy doped with carbon. It is shown that the dissolved hydrogen increases the parameter η for the FeNi structure by 25% at a constant temperature T K . It is shown that the procedure of doping with carbon (0.26 wt.%) leads to an increase in T K by 12–15°K. In the doped N36 alloy, the ultimate strength σu increases from 300 to 360 MPa at 293°K and the additional heat treatment in hydrogen aimed at the atomic ordering enables us to increase σu to 440 MPa. The plasticity of the samples remains practically constant ( δ = 20%). The physical mechanism of the outlined influence of interstitial impurities is proposed.

Influence of interstitial impurities on the Griffith work in Ti-based alloys

The influence of interstitial B and C impurities on grain boundary cohesion in the series of B2-TiMe alloys, where Me = Fe, Co, Ni or Pd, was investigated using the plane-wave pseudopotential method within density functional theory. The most preferential sites for interstitial impurity atoms at the TiMe Σ5(310) symmetrical tilt grain boundary were determined. It was shown that the impurities’ sorption energies at the grain boundary depend strongly on their local environment. Analysis of the electronic properties allows us to reveal the microscopic nature of the chemical bonding of B and C at the grain boundary. It was shown that, in contrast with hydrogen, both impurities decrease the grain boundary energy more significantly than the surface one. This results in an increase in the Griffith work which also indicates the strengthening of the grain boundary. Our estimation of the Griffith work for the TiMe alloy containing both B and H atoms shows an increase in comparison with the undoped alloy, but the effect of carbon on grain boundary strengthening in the presence of hydrogen seems to be negligible. The contributions of the chemical and elastic mechanisms to the Griffith work are discussed.

Influence of Interstitial Impurities on Deformational Behavior and Fracture Mechanism of Submicrocrystalline Titanium at Room and Elevated Temperatures

General trends and other aspects of the deformational behavior, localization of plastic deformation on the macroscale level, and fracture of submicrocrystalline and coarse-grained titanium with different interstitial impurity levels are established. It is shown that for the submicrocrystalline structure as well as for the coarse-grained structure, strengthening by interstitial impurities decreases with increase of the deformation temperature. Experimental data are presented which indicate that in the development of grain-boundary sliding in submicrocrystalline titanium with simultaneous onset of recrystallization, a high degree of plastic deformation is reached before fracture occurs, where the deformational behavior and localization of plastic deformation on the macroscale level are analogous to the same processes under superplastic flow.

The influence of interstitial impurities on true grain-boundary sliding of titanium in coarse-grained and submicrocrystalline states

The structure and temperature dependence of low-frequency internal friction of Grade-2 and Grade-4 titanium specimens following equal-channel angular pressing is investigated. It is established that specimens of both grades in submicrocrystalline states possess a high fraction of high-angle boundaries (η ~ 70%) for the average grain size d ~ 0.8 μm. Formation of this structure results in a much lower temperature of initiation and development of true grain-boundary sliding compared to the coarse-grained titanium. It is noted that the grain-boundary sliding activation energy in submicrocrystalline titanium increases with the impurity concentration from 74 ± 4 (Grade-2) to 88 ± 4 (Grade-4) kJ/mol, but is found to be much lower for the coarse-grained recrystallized titanium (140 ± 4 kJ/mol).

The influence of interstitial impurities on temperature ranges of deuterium retention in austenitic stainless steel 18Cr10NiTi

The influence of nitrogen, oxygen and helium on the temperature range of deuterium retention in 18Cr10NiTi stainless steel (of AISI304L type) has been investigated. It is demonstrated that the introduction of oxygen, nitrogen or helium into 18Cr10NiTi steel extends the upper limit in the high-temperature range of deuterium retention. It has been found that for 18Cr10NiTi stainless steel, pre-irradiated with helium ions, the increase in the temperature range of deuterium retention occurs in steps: on attainment of helium concentration of ∼0.5 at.% He the temperature range increases by ∼100 K, and on attainment of helium concentration of ∼2.5 at.% He the temperature range increases by ∼350 K. The introduction of oxygen into 18Cr10NiTi stainless steel results in the increase of the temperature range of deuterium retention in the direction of rise in temperature. In the deuterium thermodesorption spectrum, this manifests itself by the occurrence of an additional low-amplitude peak with the maximum temperature T m ∼ 560 K. The introduction of nitric impurity into 18Cr10NiTi stainless steel results in the extension of the temperature range of deuterium retention towards higher temperatures.

Influence of interstitial impurities on the valence electron structures and phase transformation behavior in intermediate Ti–Al alloys

Development of intermetallic compounds in Ti–Al alloys for high-temperature structural applications has long been impeded due to their embrittlement. To overcome the embritttlement, it is necessary to understand thoroughly its chemical bonding nature and the resultant phase transformation behavior. In this study, based on the Empirical Electron Theory of Solids and Molecules (EET), effects of interstitial impurities on the valence electron structures and phase transformations in the intermediate Ti–Al alloys were investigated. It was demonstrated that for such alloy systems, because interstitial impurities can enhance the hybridization states of Ti and Al atoms, the valence electron structures of various phases became considerably anisotropic. As a result, some phase transformations at high temperatures was hindered, leading to the occurrence of complex metastable phases at the room temperature. Such theoretical calculations clarified some unclear results from experimental observations in the literature.

Change of the superconducting, transport, and microscopic properties of transition metals upon introduction of interstitial impurities and deformation-induced defects

For group-V transition metals (Nb, Ta) containing different concentrations of interstitial impurities (O, C, N, H) and deformation-induced defects, a numerical calculation of various effective microscopic characteristics averaged over the Fermi surface and of the band parameters in the framework of the Friedel model is carried out using the experimentally determined values of the superconducting transition temperature Tc and the temperature dependence of the resistivity in the interval Tc<T≲300 K. The causes of the polar character discerned in the influence of interstitial impurities and dislocations on the investigated physical characteristics are discussed.

The influence of crystallographic texture and interstitial impurities on the mechanical behavior of zirconium

Development of physically based constitutive models capable of simultaneously describing slip, twinning, and anisotropy requires knowledge of the coincident influence of each on mechanical response. In this article, the influence of interstitial impurities and texture on twinning in zirconium (Zr), in addition to variations in strain rate and temperature, are examined, to probe their effects on substructure evolution and mechanical behavior. The compressive-yield responses of both high-purity (HP) crystal-bar and lower-purity (LP) zirconium were found to depend on the loading orientation relative to the c-axis of the hcp cell, the applied strain rate, which varied between 0.001 and 3500/s, and the test temperature, which varied between 77 and 298 K. The rate of strain hardening in zirconium was seen to depend on the controlling defect-storage mechanism as a function of texture, strain rate, and temperature. The substructure evolution of HP zirconium was also observed to be a function of the applied strain rate and test temperature. The substructure of HP zirconium was seen to display a greater incidence of deformation twinning when deformed at a high strain rate at 298 K or quasi-statically at 77 K.

The effect of impurity content on thermally activated deformation in NiAl single crystals

NiAl-base materials are attractive candidates for high temperature structural applications due to their low density, excellent oxidation resistance and high thermal conductivity. However, in single crystal and polycrystalline form, NiAl suffers from low tensile ductility and toughness. The mechanisms responsible for the limited ductility of NiAl single crystals are still in question. For this reason, thermally activated deformation in NiAl single crystals has been studied with the use of strain-rate change experiments. The preliminary results suggest that the intrinsic mobility of a , and to a lesser extent a dislocations, is limited below the DBTT in NiAl. To examine the influence of interstitial impurities and the possibility that strain-aging embrittlement is the mechanism responsible for the limited ductility of NiAl, further experiments on high purity NiAl crystals have been conducted for comparison to the results on commercial purity crystals.

A study of the chlorine nuclear quadrupole resonance frequency spectrum in potassium hexachloro-osmate by Fourier transform methods

A study of the chlorine nuclear quadrupole resonance spectrum of K2OsCl6 in the vicinity of the structural phase transition using Fourier transform techniques is reported. At high temperatures a single symmetric line spectrum is observed as expected from the high temperature cubic antifluorite structure. Below Tc = 45 K the two symmetric line spectrum characteristic of a tetragonal distortion is seen. At intermediate temperatures, 45 < T < 150 K the spectrum consists of a single asymmetric line. A detailed analysis reveals that for the single crystal sample the asymmetric line is composed of two symmetric components, a main line, and a weak satellite shifted −1.5 kHz relative to the main line. This feature is unaffected by changes in temperature near Tc. It is attributed to the influence of interstitial impurities on neighbouring chlorine ions. For the powder sample, the asymmetry is qualitatively different. A detailed analysis shows that the line is a superposition of three components. In addition to the two components present in the single crystal, a third, broad component develops as the temperature approaches Tc. This feature of the spectrum is the cluster induced order-disorder manifestation of the local dynamics. The most probable reason that this third component is not observed in the single crystal spectrum is because it is too broad due to a difference in the detailed dynamics of the two samples.

The isotope effect and the influence of interstitial impurities on the hydrogen solubility limit in niobium and vanadium

The solubility limits for hydrogen and deuterium in niobium were determined resistometrically between 175 and 280°K before and after purification of the niobium by ultra-high vacuum treatment. No isotope effect was observed; neither was an interstitial impurity effect detected in the low concentration range studied. The solubility limits for hydrogen in vanadium were measured at temperatures between 230 and 325°K before and after additions of oxygen greater than 1000 at. ppm. Large concentrations of solute oxygen increase the apparent solubility limit for hydrogen in vanadium.

Influence of interstitial impurities on the magnetic properties of pure iron

Iron-carbon alloys with bcc structure were prepared in different gas mixtures by gas-carburizing. Special care was taken in order to achieve homogeneous carbon distribution. Viscosity field and anisotropy field measurements were made on samples containing different amount of carbon interstitials to test the theoretical relationship between the viscosity field and induced anisotropy.

Influence of interstitial impurities on defect production and recovery in niobium neutron-irradiated at 4.6 K

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Superconductivity of heat-treated Nb-65 at.% Ti alloy

Brief reviews are given of the effect of heat-treatment on the microstructure of cold-worked bcc metals and the superconducting properties of niobium alloys. Particular attention is paid to the influence of interstitial impurities in these processes. The annealing effects in microstructure and superconducting properties of a cold-worked Nb-65 at.% Ti alloy, containing oxygen as a major impurity, have been studied. The precipitation process takes the form βTiNb + O2→ various Ti oxides → αTi + TiO. Differences in precipitation sequence are described for vacuum-annealing and annealing in impure argon. Flux-pinning is related to the microstructural observations. At least three pinning mechanisms appear to operate; dislocation pinning and two types of precipitate pinning. These observations are in accord with previously proposed pinning models.