Specimens of aluminum and Al-Li alloys were irradiated with a polyenergetic (2-20 keV) flux of fast hydrogen particles generated in a high-voltage glow discharge. Concentration profiles of hydrogen (in relative units) absorbed by Al and its alloys are obtained for depths up to 13-14 μm using the SIMS method. Trapping of hydrogen atoms depends on the chemical composition of alloying additions in the alloy.
The behaviour of sandwich structures of cold cathodes has been studied in a glow discharge. The differences in the behaviour of the cold-cathode composite structures under the action of a glow discharge in a helium-neon mixture are discussed.
The variation in surface microrelief of the aluminum-lithium alloy Al-2% Li-2.5% Cu and pure aluminum as a result of irradiation by powerful pulsed hydrogen-plasma fluxes at heat-flux densities of 105-5·106 W·cm-2 and pulse length 20 μsec is investigated on a Desna unit. The minimum heat-flux density from the high-temperature plasma required to initiate surface melting of aluminum materials is determined. The temperature and corresponding vaporization rate from the sample surface are estimated for several characteristic heat-flux densities.
It has been investigated the corrosion resistance, strength and plasticity of vanadium-based ternary (V-Ti-Cr) alloys in a steam–water medium. It has been found the optimum compositions with the best properties.
The features of manufacturing composite alloys for secondary- electron emitters on the base of noble metals (platinum, palladium, silver) with alkaline and rare earth metal additives are considered. The effect of surface charging on the measurement of the emission characteristics of the materials is analyzed. Optimum properties distinguish composite alloys with lithium oxide additives.Reaxys Database Information |
The corrosion resistance of aluminothermic vanadium and vanadium-based binary (with 10 and 35 at. % Ti) and ternary (V–Ti–Cr) alloys in lithium is studied upon neutron irradiation. Samples of the alloys sealed in lithium-filled ampules are irradiated with fast neutrons to a fluence of 1023 cm–2 at 350–830°C in a BOR-60 reactor. It is found that the concentration of interstitial impurities (oxygen and carbon) at the surface of vanadium alloys upon irradiation is higher than that in the alloys studied under static conditions. When the vanadium alloys operate under irradiation and attack by lithium used as a heat-transfer medium, a high contamination of the surface layers in the alloys with interstitial impurities and their effect on the physical and mechanical properties of the alloys it should be taken into account.
The vacancy migration energy in fcc metals is calculated using a modified embeddedatom method and with allowance for the relaxation of the atoms nearest to a vacancy. The calculated energies are close to the experimentally determined vacancy migration energies. Taking into account the relaxation of the atoms nearest to a vacancy makes it possible to find a relation between the sublimation energy of a metal and the calculated vacancy migration energy. This relation is shown to correlate satisfactorily with the experimental relation between these parameters.
A technology for sintering electron sources (emitters) consisting of a metal (base) and an active component is considered, and optimal sintering conditions are determined. Group-VIII metals (nickel, copper, platinum) are used as the base, and mixtures of barium, magnesium, beryllium, and lithium oxides as the active component. The secondary-emission characteristics of the electron sources are investigated. Oxide mixtures with BaO:MgO:BeO = 8:5:2 and BaO:Li2O = 1:5 have the best secondary-emission properties. Optimal emitter-activation conditions are obtained, as well as the dependence of the emission characteristics on the structure of the source and the content of active components. The emission characteristics are stable under electron bombardment.
The results of the irradiation of the Inconel 718 alloy with pulsed helium ion and helium plasma fluxes at a power density q = 107 W/cm2 and a pulse duration τ ≈ 100 ns in the Vikhr Plasma Focus setup are presented. The surface layer is not melted under the irradiation conditions. However, a slight increase in q causes melting of local regions in the surface and the formation of a wavy relief. Beam–plasma irradiation results in structural and phase changes in the irradiated surface layer, namely, the precipitation of microinclusions (complex niobium carbides), a redistribution of alloy elements, a slight decrease in the microhardness, and, accordingly, slight softening. These changes in the microstructure and the properties are determined by the melting of the irradiated surface in local regions, partial sputtering of solid-phase regions, and recrystallization in the near-surface layer during pulsed heating for each beam–plasma action.
The effect of powerful pulsed fluxes of nitrogen plasma and nitrogen ions generated in the PF-4 Plasma Focus setup (LPI; energy flux density of plasma pulse was 108–1010 W/cm2) on the modification of vanadium surface is studied. Melting and ultrafast solidification result in a fine cellular structure (cell size of 100–200 nm) in a thin surface layer in samples. There are irradiation regimes causing directional crack growth after solidification and cooling of the surface layer and the formation of a block microstructure with a block size of several tens of micrometers. The thickness of the melted layer in the samples is 2–4 μm. Cracks propagate to a depth of 5–20 μm. It is established that irradiation by pulsed nitrogen plasma and high-energy nitrogen ions changes the microhardness of the vanadium surface layers. The microhardness increases by a factor of three with the number of plasma pulses and the distance between a sample and the anode of the Plasma Focus (PF) setup. The increase in the microhardness is in agreement with the refinement of coherent scattering regions, the increase in lattice microstrain ε, and the formation of vanadium nitrides. Pulsed fluxes of nitrogen plasma and nitrogen ions decrease the lattice parameter much greater than cold working (rolling) does. The lattice parameter decreases when the total irradiation power is increased (the number of pulses increases or the distance between a sample and the anode of the PF setup decreases). Such changes seem to be caused by the action of the residual macrostresses induced by pulsed plasma irradiation. In addition, X-ray diffraction analysis showed a change in the texture of the surface layer after ion-plasma treatment of coldworked vanadium samples in the PF setup.
The effect of the relief and the emission properties' nonuniformity of a cathode surface upon the distribution of ion current is studied.
For modelling thermodynamic properties of the Fe–Cr alloys necessary to know the concentra tion dependences of the Debye temperature, the lattice parameter, the elastic moduli, the average magnetic moment, and the Curie temperature. The investigations are performed on iron alloys with chromium or vana dium in the concentration range 2–8 at %. The lattice parameters of the alloys are determined by comparing them with a standard sample placed on the surface of the sample under study. As the standard, a silicon crystal is used, and its lattice parameter is measured by the highprecision Bond method. The Debye temperatures of the alloys are determined from the temperature dependences of the integrated Xray diffraction line inten sities. The specific magnetization is measured by the Faraday method to compare the magnetic properties of Fe–Cr and Fe–V alloys. The partial magnetic moment of the iron atom is shown to increase with the alloy ingelement concentration.
Thermodynamic analysis of the chemical and phase compositions of uranium–plutonium nitride (U0.8Pu0.2)N0.995 irradiated by fast neutrons to a burn-up fraction of 14% shows that a structure, which consists of a solid solution based on uranium and plutonium nitrides and containing some elements (americium, neptunium, zirconium, yttrium, lanthanides), individual condensed phases (U2N3, CeRu2, Ba3N2, CsI, Sr3N2, LaSe), metallic molybdenum and technetium, and U(Ru, Rh, Pd)3 intermetallics, forms due to the accumulation of metallic fission products. The contents and compositions of these phases are calculated. The change in the chemical and phase compositions of the irradiated uranium–plutonium nitride during the β decay of metallic radioactive fission products is studied. The kinetics of the transformations of 95Nb41N, 143Pr59N, 151Sm62N, and 147Nd into 95Mo42 + Ns.s., 143Nd60N, 151Eu63N, and 147SmN, respectively, is calculated.
The influence of oxide film upon the operation of secondary-emission cathodes (SEC), made of oxidized metals and alloys, is studied theoretically for the conditions of electron bombardment. The expediency of applying aluminium and its alloys with low roughness of the oxidized surface for the SEC manufacture is substantiated.
The interaction of uranium mononitride UN with a refractory metal (rhenium) is studied in the temperature range 1773–2273 K. The coefficients of uranium diffusion from UN into polycrystalline and singlecrystal rhenium and their temperature dependences are determined. The diffusion mobility of uranium in rhenium is shown to be lower than that in molybdenum and to be higher than in tungsten.