Practical Approbation of Thermodynamic Criteria for the Consolidation of Bimetallic and Functionally Gradient Materials

This study concerns the key problem of determining the conditions for the consolidation or fracture of bimetallic compounds and high-gradient materials with different coefficients of thermal expansion. The well-known approach to determining the strength is based on the assessment of the critical energy release rates during fracture, depending on the conditions of loading (the portion of shear loading). Unfortunately, most of the experimental results cannot be used directly to select suitable fracture toughness criteria before such a connection is made. This especially applies to the region of interphase interaction, when it is required to estimate the internal energy of destruction accumulated during the preparation of the joint in the adhesion layer within the range of 20–50 μm. Hence, criteria for the adhesive consolidation of bimetallic compound layers were obtained on the basis of the thermodynamics of nonequilibrium processes. The analysis of the quality of the joint using the obtained criteria was carried out on the basis of the calculation of isochoric and isobaric heat capacities and coefficients of thermal expansion of multiphase layers. The applicability of the criteria for the qualitative assessment of the adhesion of layers is demonstrated in the example of bimetallic joints of steel 316L—aluminum alloy AlSi10Mg obtained by the SLM method at various fusion modes.

Mathematical Model of the Deaeration of Finely Dispersed Solid Media in a Spherical Matrix of a Roller-Type Apparatus

The additional operation of deaeration (compaction) of powders affects the quality of many products of chemical industries, the conditions for their delivery. Otherwise, energy consumption increases significantly. The aim of this work is the modeling of the deaeration of solid finely dispersed media in a gap with perforated hemispherical shapes on the surfaces of the shaft and conveyor belt within the framework of the mechanics of heterogeneous systems. A plane-deformation model is described, neglecting the forces of interphase interaction and taking into account the compressibility of a solid-particle-gas mixture without elastoplastic deformations. The model assumes consideration of the movement of (1) the components of the solid skeleton together with the carrying phase as a whole; (2) gas in an isothermal state through the pores of a finely dispersed material. This work is devoted to the study of part (a), i.e., behavior of the solid particle-gas system as a whole. The efficiency of the seal-deaerator is estimated using the obtained analytical dependencies for the main strength and speed indicators. The change in the degree of compaction of a spherical granule made of kaolin with given strength characteristics is investigated. It is shown that for the initial time interval up to 3.7⨯10−2 s, the growth of the porosity value relative to the horizontal coordinate along the conveyor belt is exponential and increases by a factor of 1.1. After eight such time intervals, the porosity values stabilize along the indicated coordinate with an increase of more than 1.4 times from the initial value.

Dynamics of interphase interaction between components during mixing

The processes of mixing, whipping, and foaming are essentially uniform and consist in dispersing the gas in a liquid. When mixing and whipping, the mixture of components is swollen due to the mechanical action; increased in volume water-insoluble protein substances (gluten proteins) form a three-dimensional spongy mesh continuous structure. It is called a gluten frame. It determines the elastic and resilient properties of the medium. Therefore, the purpose of the study is to establish the relationship between the gas holding capacity of the medium and the energy expended on the hydration of the components. The study solves the task of determining the gas holding capacity of the medium with variable parameters of the height of the liquid phase from the mixing intensity, the duration of transient processes for the formation of the full volume of the gas-liquid medium, the duration of the transient process for the dispersed gas phase yield. The difference between the levels before the gas phase formation and during the mixing (aeration) mode determines the value of the gas holding capacity. In this context, we concluded that it is expedient to completely destabilize the established modes by changing the operating modes in the working body in the flow system. An additional effect on the system is the change of hydrodynamic regimes due to the unstable dynamics of the dispersed gas phase formation. The generation of the dispersed gas phase means the presence of energy expenditure on the interphase layer formation, which should be considered in the total energy balance. At the same time, another feature should be mentioned. Part of the gas phase, which existed and continues to exist in the new mode after mixing, enters the mode of a transient process. Therefore, the most effective mixing occurs while adhering to the shifted mode for dosing components in a suspended state and the mechanical impact of the working body. Based on the given objectives and conditions of sponge dough mixing, we determined the requirements for the mixer design and found that the supply of components should last at least 45 seconds. During this period, hydration occurs and energy consumption is declining.

Comparing features in metallurgical interaction when applying different techniques of arc and plasma surfacing of steel wire on titanium

This paper reports a study into the regularities of interphase interaction, features in the formation of intermetallic phases (IMPs), and defects when surfacing steel on titanium in four ways: P-MAG, CMT, plasma surfacing by an indirect arc with conductive wire, and PAW. A general tendency has been established in the IMP occurrence when surfacing steel on titanium by all the considered methods. It was determined that the plasma surfacing technique involving an indirect arc with conductive wire is less critical as regards the IMP formation. That makes it possible to obtain an intermetallic layer of the minimum thickness (25...54 μm) in combination with the best quality in the formation of surfaced metal beads. Further minimization of the size of this layer is complicated by a critical decrease in the heat input into the metal, which gives rise to the capability of the surfaced metal to be collected in separate droplets. The formation of TiFe2, TiFe, and the α-Fe phase enriched with titanium in different percentage compositions has been observed in the transition zone of steel surfacing on titanium under different techniques and modes of surfacing. The study has shown the possibility of formation, in addition to the phases of TiFe2 and TiFe, the Ti2Fe phase at low heat input. The technique of plasma surfacing by an indirect arc with conductive wire minimizes the thermal effect on the base metal. When it is used at the border of the transition of the layer of steel surfaced on titanium, the phase composition and structure of the layers in some cases approach the composition and structure of the transition zone of the original bimetallic sheet "titanium-steel" manufactured by rolling. A layer up to 5 μm thick is formed from the β phase with an iron concentration of 44.65 % by weight and an intermetallic layer up to 0.2...0.4 μm thick, close in composition to the TiFe phase. The next step in minimizing the IMP formation might involve the introduction of a barrier layer between titanium and steel.

Characterization of a Bimetallic Multilayered Composite “Stainless Steel/Copper” Fabricated with Wire-Feed Electron Beam Additive Manufacturing

The results of investigating the structure and properties of multilayered bimetallic “steel–copper” macrocomposite systems, obtained by wire-feed electron beam additive manufacturing, are presented in the paper. The features of boundary formation during 3D printing are revealed when changing the filaments of stainless steel and copper. Inhomogeneities in the distribution of steel and copper in the boundary zone were detected. Interphase interaction occurs both in the steel and copper parts of the structural boundary: Cu particles with an average size of 5 µm are formed in the iron matrix; Fe particles with an average size of 10 µm are formed in the copper matrix. It was revealed that such structural elements, as solid solutions of both copper and iron, are formed in the boundary zone, with additional mutual dissolution of alloying elements and mechanical mixtures of system components. The presence of the disc-shaped precipitations randomly located in the matrix was revealed in the structure of the “copper–steel” boundary by transmission electron microscopy; this is associated with rapid cooling of alloys and the subsequent thermal effect at lower temperatures during the application of subsequent layers. The existence of these disc-shaped precipitations of steel, arranged randomly in the Cu matrix, allows us to draw conclusions on the spinodal decomposition of alloying elements of steel. The characteristics of mechanical and micromechanical properties of a bimetallic multilayered composite with a complex formed structure lie in the range of characteristics inherent in additive steel and additive copper.

Heat-mass transfer simulation of fluid media in the magma channel

<p>The paper presents a non-stationary model of heat-mass transfer of heterophase media in application to the study of the intrusion processes of magmatic melts in permeable zones of the lithospheric mantle and crust. Special emphasis is given to the study of the change in rheological properties of the fluido-magmatic mixture in the process of magmatic channel formation. The increased compressibility of the fluid phase is taken into account in the model by setting the Van der Waals equation of state. The calculated values of thermodynamic parameters of the fluid-magmatic system such as pressure, temperature, volumetric phase content, are the basis for the analysis of metasomatic changes in mantle matter. The Numerical model is based on the Runge-Kutta-TVD method. Verification of the numerical model on standard tests shows good accuracy of the program code and the possibility of using it for investigations of the currents of fluid-magmatic flows. The study of variation in interphase interaction parameters during melt movement in permeable zone, including change in interphase viscous friction, demonstrates a significant change in temperature distribution in the section of fluid-magmatic system. The work was financially supported by the Russian Foundation for Basic Research, grants No. 19-05-00788.</p>

Method of operational life’s increasing of transport’s parts due to usage of coatings based on epoxy matrix modified by maleinic anhydride with improved thermal physical properties

The use of a new method of operational life increase of the transport means parts due to the introduction of polymer-based modified materials has been substantiated in the paper under discussion. It is shown that the use of matrices based on epoxy diane oligomers is quite promising direction in protective coatings formation. Some active additives have been applied to improve the properties of epoxy matrices on preliminary stage of their formation. The use of maleinic anhydride modifier containing active to the interphase interaction functional groups is promising as well. Epoxy diane oligomer has been used as the main component for the matrix in the composite formation. The hardener polyethelenepolyamine has been used to link the epoxy compositions enabling to harden the materials at room temperature. The choice of maleinic anhydride as a modifier to improve thermal-physical properties of the developed materials has been substantiated. It has been found that to form a composite material or a protective coating with improved thermal-physical properties it is necessary to apply maleinic anhydride as a modifier in epoxy matrix in the following ratio: q = 0,5 pts.wt. per q = 100 pts.wt. of epoxy oligomer ЕД-20. In this case the material has been formed where, comparing with nonmodified matrix, the indices of glass transition temperature are being increased from Тс = 327 К tо Тс = 335 К, heat resistance (by Martenson) from Т = 341 К to Т = 362 К, and thermal coefficient of linear expansion in the range of temperatures ∆Т = 303…423 К is being decreased from α = 9,9 ×10-5 К-1 to α = 4,4 ×10-5 К-1. It has been proved that the maleinic anhydride content in the matrix with its small fraction (q = 0,5 pts.wt.) has activated the processes of interphase interaction in epoxy CM structure formation, resulted in the increase of number of both physical and chemical bonds per polymer volume unit. This process will involve the increase of gel fraction degree in CM, and, correspondingly, both the cohesion and thermal-physical properties of modified CM have been improved. The developed material under discussion could be efficiently used as a matrix in formation of protective coatings which are to be operated under high temperatures conditions and dynamic or static loadings.

TOWARDS THE PRESENCE OF REGULARITIES BETWEEN THE FUNCTION OF INTERFACIAL INTERACTION AND THE FILTRATION CAPACITY PROPERTIES

This paper discusses the results of identifying possible regularities between the parameters describing the function of interfacial interaction and filtration capacity properties of rocks. The studies have employed real laboratory data, forming four clusters. The capillary pressure curve data and relative phase permeability data were obtained on the same core samples. The authors describe the factors determining the interphase interaction during multiphase fluid flow in a porous medium. On this basis, a method for calculating discrete values of the interfacial interaction function based on the results of laboratory studies of relative phase permeability is proposed. For the approximation of the interfacial interaction function, the four-parametric formula following from derivative of Buckley — Leverett function at assignment of relative phase permeability functions by means of Corey functions is substantiated. The authors suggest two variants of interphase interaction function formulation. They prove that for the first variant, there is a stable dependence only for one parameter, and for the second variant — with three parameters. Thus, one of the parameters in all cases has appeared close to one. The results show that the error of the detected dependencies on the deviation of the parameters has a linear dependence, and for both variants of the interfacial interaction function, the ranking of the parameters is different according to their influence on the error. Using a test sample, the authors show that the dependencies obtained allow determining the parameters of the interphase interaction function with an acceptable error.