Russian Metallurgy (Metally)最新文献

The article describes the results of tool wear tests of a tool for deformational cutting in external finning of copper heat-exchange tubes. The test method and equipment are presented. The tool wear topography is analyzed, the tool wear criterion is determined, and graphs of changes in linear and mass wear parameters are constructed. The tool wear life was 90 min at a cutting path of 13.3 km. A three-tool copper tube finning machine with the given tool life provides finning of 368 linear meters of tubes.

Theoretical investigation demonstrates that the effect observed during crystallization under isostatic pressure is determined by how the atoms involved interact with each other and how they form particular compounds. We formulate concepts that are used as a basis for a model of a crystal lattice in an equilibrium state without any external influences. A system of equations is derived which allows one to find the key parameters characterizing the configuration of the outer electron shell of an atom under isostatic pressure. The main parameters describing the electron density distribution of the native shells of an atom are determined.

The structure of modified layers in carbon steels after thermodiffusion zinc coating in an ammonia atmosphere was studied. Theoretical analysis of phase diagrams identified the possible phases in the Fe–Zn–N system, including solid solutions, intermetallics, and nitrides. Metallographic, electron microscopic, and Auger electron spectroscopic analyses showed that diffusion zinc coating in ammonia produces modified layers consisting of an outer coating based on chemical compounds and a diffusion layer of solid solutions with a transition zone. Parallel nitriding of steel and an increase in layer microhardness due to solid-solution strengthening were observed.

The study describes the unusual auxetic and magnetostrictive behavior of binary iron-based alloys: galfenol Fe_{100 – x}Ga_x and alfenol Fe_{100 – x}Al_x. We present experimental and theoretical results explaining the intrinsic auxetic properties of galfenol and alfenol in the range 0 < x < 27.2. Theoretical conditions for achieving negative Poisson’s ratios in body-centered cubic metals are presented, along with calculated values of Poisson’s ratios and Young’s moduli for galfenol and alfenol as functions of the atomic percent of Ga and Al incorporated into the iron alloy matrix. The study attributes the negative Poisson’s ratios to elastic anisotropy, that is, the difference between the tetragonal C ' and rhombohedral C₄₄ elastic moduli in a cubic single crystal. Experimental results on the anisotropic magnetostrictive behavior of galfenol and alfenol are described as a function of the applied magnetic field direction. Concentration dependences of tetragonal and rhombohedral magnetostriction for galfenol are provided. The study associates the unusual behavior in a magnetic field with differences in the phase composition of the alloys. Magnetoelastic behavior is examined, and correlations between the elastic moduli C₁₁, C₁₂, C₄₄, the magnetoelastic constants b₁ and b₂, and the magnetostriction λ in cubic crystals are identified.

This paper outlines the specific features of high-strength cast iron (SGI) structuring with or without late graphitizing modification, the specifics of graphitizing modification, and the factors that determine the modification treatment. A detailed review is provided of the factors that facilitate the modification of the melting process, the factors that affect the choice of method and materials for the modification treatment, the factors that stimulate the growth of graphite inclusions, and the results of the aging process of the modifying effect in the cast iron melt. Polynomial dependences are given of the effect of magnesium content on the number of graphite globules and shrinkage in SGI, and of graphitizing modifier consumption on chilling of cast iron and the number of graphite globules. The main causes of chilling of cast iron are also specified. The primary features of the spheroidization mechanism of graphite inclusions are described along with an explanation of the mechanism of their formation and growth. Basic ladle magnesium treatment methods for cast iron melt are listed, and their efficiency for SGI production is characterized. One of the effective ways of SGI production using the ladle and lid technology is analyzed in detail. Chemical elements introduced into graphitizing modifiers are classified by efficiency. Compact graphite iron (CGI) is characterized in general, and the main problem of its production is indicated. Polynomial dependencies of the key mechanical properties of CGI and of thermal conductivity on the content of spheroidal graphite (SG) therein are shown. Five most common methods of CGI production are listed. The main features and characteristics of the CGI production method by ladle modification with magnesium/REM-containing modifier are described. The furnace and final in-cast chemical compositions of CGI are recommended. Polynomial dependences of the magnesium/REM-containing modifier charge and holding time of the cast iron melt treated with a modifier on graphite compactness degree (GCD) are shown.

The possibility of using the results of studying the stress–strain state of a metal in the deformation zone during the formation of axisymmetric flanged forgings made of an AMg6 aluminum alloy with an internal cavity is considered. The forgings are formed under hot isothermal stamping in a single operation using a standard hydraulic press with a nominal force of 2.5 MN. The stress–strain state is investigated by mathematical modeling based on computational and full-scale experiments. Defect formation is evaluated using the Hartfield field and the QForm software. An algorithm for predicting defect formation has been developed. Its practical application is recommended for designing the technological process of hot isothermal forging of hollow flanged axisymmetric products made of an AMg6 aluminum alloy.

The effect of chromium carbide and graphite present in a flux cored wire charge on the structure of deposited metal, which was fabricated by arc surfacing using a filler wire, is considered. Chromium carbide is found to be mainly destroyed; however, as the graphite content in the flux cored wire charge increases, the stability of carbides increases. The destruction of chromium carbide during surfacing process allows us to alloy the deposited metal with chromium and carbon, which allows a hypereutectic structure to form at a certain composition of a flux cored wire. The hardness of the deposited metal changes slightly.

The study examines how surface roughness depends on manufacturing parameters, using as an example a powder feed shaft produced by additive manufacturing with fused deposition modeling/fused filament fabrication (FDM/FFF) technology. The work presents an analysis of the properties and selection of PLA and PETG engineering polymers. The results provide roughness values for specimens fabricated by FDM at different build angles and layer heights, and they show how the roughness of printed parts influences the flowability of metal powder compositions. These findings demonstrate the feasibility of producing FDM parts with surface roughness parameters specified at the design stage.

The features of processing the surfaces of parts with various external contours using an unbound grinding medium are described. A schematic solution of the method and the results of its practical implementation are provided. The dynamic characteristics of the process are investigated. Mathematical models for determining the pressure of a compacted abrasive medium on the surface of a workpiece and the cutting speed are presented.

The research works on the modeling and numerical algorithmization of combustion processes, the formation of secondary structures and the mechanisms of associated transient processes revealed that resonance can be avoided due to skip from local equilibrium manifold by turbulization of the laminar process during thermal pumping. In the case of a single active component, the global heterogeneity of a system can be characterized as a nonuniform enthalpy distribution over the flow (mixture). The results of numerical experiment show that the turbulization of combustion process during thermal pumping, as well as for vibrational combustion, leads to the formation of a vast .time zone of detonation combustion in the vicinity of thermal explosion resonance.