The process of grain refinement under severe plastic deformation was examined in an Al–5.4% Mg–0.5% Mn–0.1% Zr alloy, which was subjected to equal-channel angular pressing (ECAP) in the strain ...interval from 1 to 12 at a temperature of ∼300
°C. It was shown that the size and distribution of the second phase particles precipitated under homogenization annealing strongly affect grain refinement. Extensive grain refinement under ECAP was provided by a dispersion of Al
6Mn particles with an average size of ∼25
nm that precipitated during the homogenization annealing at an intermediate temperature. The fully recrystallized structure with an average crystallite size of ∼0.55
μm evolves through continuous dynamic recrystallization. In contrast, homogenization annealing at a high temperature leads to the formation of coarse Al
6Mn particles with a plate-like shape. Under further ECAP, the formation of coarse recrystallized grains takes place in this material due to the discontinuous growth of recrystallized grains during the inter-pass annealing between the ECAP passes. The role of second phases in grain refinement is discussed in terms of pinning and driving forces for recrystallization.
Systematized information on the formation of all types of diamond placers in the Vishera diamondiferous zone is given for the first time. The method of retrospective restoration of the ...diamond-bearing deposits made it possible to identify the five major stages of their genesis: modern, Neogene–Quaternary, Mesozoic–pre-Neogene, and Lower Silurian. Modern and Quaternary placers are represented by alluvial and deluvial–proluvial deposits consisting of almost unaltered Neogene–Quaternary formations. In terms of mineral composition, Cenozoic (Neogene–Quaternary) deposits are inherited from the Riphean–Vendian to Neogene deposits, repeatedly redeposited in different epochs of denudation. Due to fluvioglacial processes, earlier diamond-bearing deposits were eroded a few times and products of erosion were transported to other areas of the zone without significant changes. The Mesozoic giant diamond-bearing karst landforms are composed of deposits, formed as a result of erosion of the contact zones between the Polyudov–Kolchim rocks with the Takata basal unit with dolomites inside the Kolchim Formation. In general, the diamond-bearing sandy deposits of the Lower Silurian basal unit and the Takata Formation have no lithological or geochemical links. The Takata deposits are mainly alluvial, while the Lower Silurian ones are coastal marine. Geophysical methods make it possible to outline the lithofacies area, which will indicate possible kimberlite fields of the Russian Plate or unknown intermediate diamond collectors.
The types of igneous sulfide ores on the western flank of the Oktyabr’skoe deposit and the patterns of their distribution were studied. The ore-bearing rocks were investigated within the western ...branch of the Kharaelakh intrusion of the Talnakh ore field. The morphology of the ore bodies is described and mineragraphic characterization of ore types in the western part of the Kharaelakh intrusive is given based on recent drilling data. The data of earlier studies on the types of ores and their spatial distribution on the flanks of the Oktyabr’skoe deposit are summarized and confirmed. The main regularities of the spatial distribution, composition, and morphology of Cu–Ni sulfide ore bodies on the western flank of the Oktyabr’skoe deposit, which may be applied as prospecting criteria for further exploration, are identified.
▶ W, V, Nb was added in the 18Cr–9Ni steel. ▶ Solute atmosphere of W, V, Nb formed around dislocations. ▶ Dynamic strain aging (DSA) was found to occur in the temperature range 530–680°C. ▶ DSA ...increases strength of the modified 18Cr–9Ni due to formations of the clouds of solutes around the dislocations that exert the solute drag force.
Mechanical behavior and microstructural evolution of a 2.5%W+0.4%Nb+0.3%V+0.17%N modified 18Cr–8Ni austenitic steel was studied in the temperature interval 410–740°C at initial strain rates ranging from 6.7×10−6 to 1.3×10−2s−1. The Portevin-Le Chatelier (PLC) effect attributed to dynamic strain aging (DSA) was found to occur in the temperature range 530–680°C. The PLC effect is manifested in the form of serrated (jerky) flow and planar slip. DSA increases yield strength, σ0.2, and ultimate tensile strength, σUTS, in comparison with conventional SUS304 steel due to the additional alloying that provides the formations of the clouds of solutes around the dislocations that exert the solute drag force.
The movement of a metal melt in an inhomogeneous high-frequency magnetic field is considered. A system of equations with boundary conditions defining the diffusion of the magnetic field and the heat ...conduction in such a melt in the Boussinesq approximation with account of the Joule heat released in the melt and the volume Lorentz forces acting in it is presented. The correctness of the mathematical model proposed is demonstrated. The amplitude distributions of the magnetic fields of the eddy currents induced in a metal melt, the velocity distributions of the heat flows in it, and the distribution of temperatures in the melt were calculated for the control parameters of its flow determined by the frequency and amplitude of the alternating magnetic field acting on it. The conditions under which the structure of this flow is completely determined by the parameters of the magnetic field and the problem on determination of the heat and mass transfer in the metal melt can be reduced to the calculation of its forced convection in the Lorentz force field and the temperature distribution in the melt at a definite velocity of its flow were determined.
Ultrafine grained (UFG) structure with an average grain size of ~
0.6
μm was produced in sheets of Al–Cu–Mg–Ag alloy by equal channel angular pressing (ECAP) followed by hot rolling (HR) at 250
°C. ...These sheets were joined by friction stir welding (FSW) with efficiency of about unity. The effect of severe plastic deformation (SPD), FSW and heat treatment on the microstructure and mechanical properties of the welds and sheets was examined.
► Ultrafine grained Al-Cu-Mg-Ag sheets were produced by ECAP followed by hot rolling. ► The formation of ultrafine grained (UFG) structure increases strength and ductility. ► UFG sheets were joined by friction stir welding. ► Friction stir welding retains UFG structure in the weld. ► Friction stir welding produces full-strength joint in the UFG Al–Cu–Mg–Ag alloy.
We obtain an asymptotic approximation to a moving inner layer (front) solution of an initial–boundary value problem for a singularly perturbed parabolic reaction–advection–diffusion equation with ...small advection. We separately consider the case of a continuous source (the nonlinearity describing the interaction and reaction) and the case of a source discontinuity for a certain value of the unknown function, which arises in a number of topical applications. For either problem, an asymptotic approximation to the solution is constructed and existence and uniqueness theorems for such a solution are proved.
•The convection of metal in alternating magnetic field is studied.•Significant buoyancy impact on forced convection for frequency range was found.•Maps of quasi-steady averaged flows was plotted in ...plane frequency-force parameters.•The frequency dependence of loss sensitivity to properties was found.
The averaged quasi-steady flow patterns of metal melt situated in alternating magnetic field are studied numerically. It is taken into account the buoyancy due to non-uniform heating, the intensive radiation heatsink from the melt surface and the Lorentz forces arising in conductor in the alternating magnetic field. The governing equations of the suggested mathematical model are given and the model validations are described. The flow regime maps are plotted based on analysis of melt velocity dependence on the Hartmann number and the parameter of magnetic field diffusion. Flow patterns corresponding each parameter area at the map are given and interpreted. The way of acceleration of melt motion computation is suggested.
The article proposes a new approach to improving the methodology for calculating the bearing capacity of the eccentrically compressed reinforced concrete elements for cases of their loading with ...large eccentricities. The basis of this technique is considered as a modified version of the deformation model for the reinforced concrete resistance force. The main feature of this model is the energy approach to transforming the reference diagrams of compression and concrete tension into the diagrams of non-uniform deformation, corresponding to the stress-strain state of the compressed and stretched zones of concrete in the cross section of the eccentrically compressed reinforced concrete structures. This way there is no falling branch in the concrete diagrams obtained by this method. A calculation diagram of the steel reinforcement deformation with a physical yield point was taken as a partial function, consisting of one linear and two non-linear equations. The proposed method also shows the possibility of taking into account the greatest curvature of an eccentrically compressed reinforced concrete element in the plane of its loading. The article presents all the necessary dependencies allowing the theoretical value of the carrying capacity of an eccentrically compressed reinforced concrete element determination. The results of the numerical studies performed using the design software developed by the authors for the personal computer are given.
To study the variations in the solar wind velocity during inferior conjunctions of Mercury and Earth, we analyzed 54 events in the period 1995–2012 by the superimposed epoch method. We have found a ...noticeable increase in the velocity both before and after the conjunctions as well as decrease in the velocity within 3–4 days after them (Mercury׳s “shadow”). Variations of the solar wind density in 1997–2013 show a similar character, but their dispersion is substantially larger than for the velocity. The results obtained might be used to analyze variations and to improve a forecast of the solar wind velocity and density.
•The effect of the Mercurian magnetosphere on the solar wind was studied for 54 inferior conjunctions.•Both the periods of increase and decrease in the solar wind velocity and density were reliably identified.•Therefore, influence of the Mercurian “shadow” can be observed even at the Earth׳s orbit.
PDF