Metallurgist最新文献

Evolution of the microstructure of new Al–Cu–Mg–Y(Er)–Cr alloys is studied during casting, surface laser melting, simulating selective laser melting, and subsequent homogenization annealing. A structure of surface laser melting tracks without defects of crystallization origin, in particular, hot cracks, is obtained. At the same time the track zone does not have a shrinkage cavity and porosity. The grain structure of tracks is represented by a narrow zone of columnar crystals and a zone of equiaxed crystals about 5 μm in size. During homogenization of the AlCuYMgCr–L alloy particles grow in size to approximately 500 nm, while in AlCuErMgCr–L alloy they grow to a significantly larger size of 2 μm. A common feature for both alloys is presence within aluminum solid solution of a large number of particles less than 100 nm in size. According to studies and thermodynamic calculations conducted previously, during alloy homogenization of these alloys, heterogenization should occur with nucleation of L1₂–Al₃(Zr,Y)/L1₂–Al₃(Zr,Er) and Al₄₅Cr₇ phases dispersoids.

A mathematical model of the aerodynamic and thermal processes in dry granulation of molten blast-furnace slag is developed and evaluated, and a relevant problem is formulated. The model is supposed to be used for numerical optimization of the process parameters when issuing input data for the design of the dry granulation plant.

Electromagnetic stirring is a technique of influencing the crystallization pattern of a continuously cast workpiece and suppressing the development of a number of macrostructural defects in it. In this study, technological schemes are presented for application of electromagnetic fields in continuous-casting machines (CCMs) while discussing the resultant physical effects. We present actual results on the quality of steel obtained using a roller-type EMS system installed in the secondary cooling zone of a slab CCM at Novolipetsk Iron and Steel Work.

Based on the conducted experimental studies aimed at studying the morphology and elemental composition of titanium powders for additive machines obtained by electrospark dispersion of metal waste of the OT4 alloy in propyl alcohol, it is shown that the process of rapid crystallization of molten OT4 in a liquid working medium contributes to spherical shaping of the particles containing the main elements of Ti and Al. Spherical titanium powder materials obtained from the titanium alloy OT4waste can be effectively used in additive manufacturing.

Features of high-temperature oxidation of N70VTYu-ID alloy with γ‑solid solution structure are studied. It is shown that characteristics describing this process stabilize with increasing oxidation time. The calculated oxidation activation energy is ~220,000 ± 5000 J/mol, which is comparable to the nickel self-diffusion activation energy. Influence of preliminary short-term high-temperature oxidation on alloy scale resistance is investigated. It is shown that this combined heat treatment can briefly increase N70VTYu-ID alloy scale resistance.

The impact of selective laser melting (SLM) process parameters on the porosity, microstructure, phase and chemical composition, texture, and physical-mechanical properties of orthorhombic titanium aluminide Ti₂AlNb (O-alloy) powder was studied using a range of methods, including hydrostatic weighing, scanning and transmission electron microscopy, X‑ray diffraction analysis, energy-dispersive X‑ray spectroscopy, microindentation, and compression testing. It was demonstrated that an increase in the volumetric energy density within the range of 28 to 139 J/mm³ led to the following effects: 1) increase in the relative density of the obtained O‑alloy from 97 to 99.9%, 2) intensification of axial texture with a pronounced 001 direction in the detected β/B2-solid solution, and 3) reduction in the Al content, increase in the Nb content, and lower enrichment with oxygen in the obtained samples. It was demonstrated that detachment from the build platform and longitudinal cutting of the O‑alloy results in the imbalance of residual stresses in samples synthesized on a platform, pre-heated at 200 °C, which is accompanied by the formation of cracks. This study considers the typical structural defects of the alloy, including pores, lack of fusion, and chemical heterogeneity, which are observed following SLM. A series of physical-mechanical properties of the synthesized O‑alloy samples were determined, including Vickers hardness (390–430 HV), elastic modulus (91–98 GPa), compressive yield strength (1060–1080 MPa), and compressive strain (of at least 30%). The relationship between these properties and the structural-textural state of the obtained O‑alloy samples is discussed.

The current stage of development in metallurgy is characterized by unprecedented attention to reducing CO₂ emissions. Replacement of carbon with hydrogen in smelting of cast iron is a method of reducing CO₂ emissions; however, the production of hydrogen is also associated with CO₂ emissions. The carbon monoxide utilization rate during indirect reduction in a blast furnace is 28–38%, in contrast to direct reduction, in which the utilization rate is more dependent on contact area between the reducing agent and oxides. Use of ore-coal briquettes is a promising direction for increasing the utilization rate of the reducing power of carbon in a blast furnace. The study investigates the efficiency of using ore-coal briquettes in production of vanadium cast iron from the perspective of reducing CO₂ emissions. We show that carbon consumption for direct reduction of titanium-magnetite concentrate is six times lower than for indirect reduction. Using ore-coal briquettes in blast furnace charge can reduce the specific fuel carbon consumption in production of vanadium cast iron, which will reduce CO₂ emissions.

The work presents the results of the corrosion resistance study of composite coatings obtained by cold spraying of the aluminum and boron carbide powder mixture on the surface of 08Cr18Ni10Ti austenitic steel. Their chemical and phase compositions, macro- and microstructure, as well as the effect of subsequent heat treatment are analyzed. It is shown that the corrosion of coatings in a 2% boric acid solution at 60 °C is accompanied by an increase in the sample mass and the formation of an aluminum oxide layer. The minimum mass change was observed in case of the coating heat treated at 400 °C, while an increase in heat treatment temperature leads to the intensification of corrosion destruction.

This article studies the process of laser alloying of aluminum and alloy AL25 with metals: nickel, chromium, niobium, in a melting regime. Choice of metals for the study is made according to the criterion of efficiency of melt zone filling under laser treatment. Theoretical analysis of possible intermetallic phases within Al–Ni, Al–Cr, Al–Nb systems is performed, including physical parameters and crystallographic characteristics. Experimental studies by methods of metallography and X-ray diffraction analysis allows establishment of the spectrum of phases formed during alloying of aluminum from powders of these elements. They include both aluminum-rich intermetallics, and chemical compounds enriched with alloying metal. Alloying with niobium disilicide is also investigated to reveal differences in mechanisms of introducing chemical compounds into a laser-affected zone. On alloying with NbSi₂ particles get into the melt zone directly from the powder (a mechanism of particle “flight”), and when alloying with pure metal intermetallic formation of occurs in situ during crystallization. On the basis of calculating the change in lattice spacing of aluminum the concentration of alloying metals within supersaturated solid solution is estimated. The increase in microhardness of alloying zones due to solid solution hardening and dispersion strengthening by intermetallic particles is established.

Systems theory can be used not only to assess the existing state of engineering and technological systems, but also to forecast their development. This approach implies the creation of a generalized model of the object under study taking the existing connections between its individual components into account, along with an analysis of the energetic, material, and informational resources inherent in this object. This allows selection of the most optimal solution for improving the technological system under analysis from a variety of possible options. Creation of high-entropy compounds of various compositions is an intensively developing direction of modern materials science. Due to their specific chemical composition, such materials may exhibit a unique combination of properties, thereby outperforming other types of compounds. In this work, we study structural and functional interactions in a technological system aimed at obtaining coatings by laser cladding of high-entropy materials, which are represented by the starting powders mixed in a certain proportion. The input and output parameters of the laser cladding process are established. This process is represented in the form of sequential phases, resulting in the formation of a coating on the surface of the product. The coating is characterized by both technological and specific properties, depending on the chemical composition of the starting powder components. A structural and functional scheme describing the process of coating formation from a high-entropy material during laser cladding is proposed. Connections between the input and output process parameters are demonstrated. These connections reflect the formation of specific coating properties in the process of laser cladding as a result of interaction of the powder material with the laser beam. It is noted that structural and functional schemes should be used when simulating technological processes based on mathematical models, taking the occurring transformations of substances into account.