Russian Metallurgy (Metally)最新文献

The development of surface morphology, the elemental and phase composition of surface layers, and the microhardness of a VT6 titanium alloy during treatment in a glow-discharge plasma of N⁺ ions is studied without and with heating alloy samples to 300, 500, and 700°C. The formation of thin surface layers (up to ~20 nm) during ion-plasma nitriding without heating and with heating up to 300°C is shown to be controlled by oxidation processes; at sample temperatures of 500 and 700°C, the formation is controlled by nitrogen diffusion. An increase in the treatment temperature leads to the formation of rounded block-like features on the surface, an increase in surface roughness parameter Ra, and higher microhardness values of the samples, which is attributed to the formation of the Ti₂N and TiN titanium nitrides at the surface and in the surface layers.

The stage of steel crystallization is one of the most critical in the metallurgical production process as far as arise of the future product imperfections is concerned. This paper investigates some promising directions for the development of metallurgy concerning the casting and solidification of steel ingots to be used in the production of critically important items (i.e. items with enhanced reability) for power and heavy engineering industry. The authors consider, from the standpoint of cluster growth theory, the possibility of managing the crystallization process by supplying additional external energy. In particular, the authors pointed out that electroslag heating of the hot top of the ingot which is used to increase the metal utilization factor, can be applied not only as a way to minimize the effects of shrinkage phenomena (formation of physical heterogeneity), but also as a means of managing the crystallization process and thus managing the formation of other types of heterogeneity (chemical, structural) through external electromagnetic field. The factors affecting the chemical heterogeneity of the ingot and the susceptibility of steel to segregation are described. The importance of developing an ingot technological summary that provides detailed description of the physical, chemical and structural heterogeneities throughout the ingot’s cross-section, and its application in actual production is emphasized. The authors outline ways of using such a technological summary as a source of additional information about the ingot for the subsequent processing stages (i.e. forging, heat treatment) which would help to achieve the required quality of the finished product while minimizing its cost. The considered development directions are directly related to the issue of increasing the production capabilities and reducing the costs of produced metallurgical outputs.

In this study, mullite was synthesized using the solid-phase sintering method, with coal gangue acid leaching residue serving as the silicon source and analytically pure alumina as the aluminum source. A critical aspect of the solid-phase sintering process is the effective mixing of raw materials containing silicon and aluminum components, which include hydroxides, silicon-aluminum oxides, and various types of silicates. During the calcination process, these raw materials undergo a diffusion reaction at elevated temperatures, where silicon, aluminum, and oxygen ions interdiffuse, ultimately leading to the formation of a mullite crystal structure. This paper investigates the effects of calcination temperature, holding time, and the Al/Si ratio on the synthesis of mullite products.

A comprehensive study of the primary crystallization kinetics of amorphous Co₄₁Cr₁₅Mo₁₄Fe₇C₁₅B₆Gd₂ and Co₄₁Fe₇Cr₁₅Mo₁₄C₁₅B₆Y₂ ribbons prepared by melt spinning is carried out for the first time. Differential scanning calorimetry (DSC) performed at different heating rates (5, 10, 15 K/min) showed that crystallization occurs in four stages. A crystallization mechanism consisting of two parallel processes is proposed; these are a heterogeneous n-order reaction and an m-order autocatalytic reaction, which are described by the Kamal–Sourour equation.

Using the modified phase field crystal model (MPFC-model), an analysis of dynamics of solid-liquid interfaces in solidification and melting processes is presented. Dynamical regimes for face centerd cubic (FCC) lattice invading liquid melt (solidification) and liquid propagating into a thermodynamically metastable crystal (melting) are described in terms of the dynamical moving equations obtained from amplitude expansion of the MPFC density field. A generalized form of the amplitude equations for one-mode and two-mode MPFC is obtained for the FCC crystal and for different crystallographic directions. The traveling wave solution for the front velocity is quantitatively compared with data of molecular dynamics simulation for solidification and melting of the copper FCC-lattice. The phase-field mobility and free energy parameters for Cu (copper) are quantitatively estimated.

The solidification of the surface layer of fixed-length iron cast hollow billets have been studied. The billets are produced by continuous-cyclic freeze casting without a core due to one-sided heat removal and the elimination of a liquid phase deficiency over the hollow casting formation time. This process results in a dense, defect-free structure across the wall thickness, and subsequent heat treatment ensures the required phase composition. The growing number of the manufacturers of synthetic cast iron and the abundant supply of steel scrap have generated significant interest in studying the structure formation of lamellar graphite iron melted from a charge containing at least 80% steel scrap. Computer modeling is used to construct a characteristic pseudobinary phase diagram for the melt composition of gray synthetic cast iron determined during a pouring campaign (chemical composition was determined in castings 5, 9, 12, 22). We have determined the temperature of precipitation of 0.65 primary austenite dendritic crystals and the corresponding degree of supercooling for the composition under study using the concept of cessation of dendritic growth after the formation of the maximum possible volume fraction of dendritic arms in a melt (which was developed by A.V. Il’inskii and L.V. Kostyleva for the alloys forming limited solid solutions) and geometric constructions. The microstructure of the surface zone, which consists of two regions formed by a flat substrate dendrite and dendritic crystals with developed secondary arms, is investigated. The absence of graphite and cementite inclusions in the surface zone is substantiated. The revealed features of melt solidification in the contact zone with the casting machine mold is shown to prevent a direct application of the Lapshin theory of wall solidification, in which the filling of the mold is considered as a periodic layer-by-layer flow of the melt meniscus to the mold wall during filling. According to the wall solidification theory, the mold is filled only for the first casting at the moment the entire gating system and the casting machine mold are filled. Therefore, further development of measures to improve the surface quality of hollow cylindrical castings produced by continuous-cyclic freeze casting requires additions based on an extensive series of investigations.

The possibilities of extracting associated components, primarily strategic and critically important metals, from overburden coal seams in the south of the Russian Far East have been investigated. A fundamentally new resource-saving technology has been proposed for the disposal of waste from coal mining. The application of this method for extracting valuable components from coal mining waste using pyro-hydrometallurgical techniques will allow for the inclusion of numerous carbon-based man-made materials in production processes in accordance with the principles of resource conservation and without causing significant environmental damage.

This study investigates the hot forging of a straight bevel gear shaft made from DIN 15CrNi6 steel under realistic hydraulic press conditions using DEFORM-3D simulations. A Box–Behnken design with three variables—billet temperature (1000–1200°C), punch velocity (10–60 mm/s), and friction coefficient (0.1–0.5) was used to assess their effects on forging force and billet temperature. Regression models showed billet temperature and friction were key factors for forming load, while punch velocity strongly influenced thermal retention. A multi-objective optimization using the NSGA-II algorithm yielded an optimal configuration: 1200°C, 43.8 mm/s, and 0.10, achieving a reduced maximum forging load of 106.5 tons and a heat loss ratio (HLR) of 32.5%. The results demonstrate the benefit of integrating finite element modeling with evolutionary optimization to enhance the process design for complex gear forging applications.

The influence of a production method (hot rolling, electron beam additive manufacturing (EBAM)) and subsequent heat treatment on the microstructure and corrosion resistance of a KhN62M nickel alloy (composition (wt %): 23–24 Cr, 12–14 Mo, ≤0.75 Fe, Ni for balance) in a molten salt of the 3LiCl–2KCl eutectic composition at a temperature of 650°C is studied. Hot-rolled samples are characterized by an equiaxed polycrystalline structure with an average grain size of ~150 μm and a developed network of intergranular boundaries. Some of the EBAM samples are subjected to heat treatment, namely, water quenching from 1120°C. The formation of intermetallic phases (presumably σ phase) and their role in protecting the material from corrosion damage are shown. Microstructural analysis (scanning electron microscopy with energy dispersive spectroscopy, SEM/EDS) has revealed the following key differences: EBAM samples in the as-built state have a pronounced dendritic microstructure with chemical segregation of elements (Cr, Mo) and secondary phases, which are localized in interdendritic regions and form via layer-by-layer growth during deposition. This structure decreases the corrosion rate due to the formation of microgalvanic couples, where intermetallic phases act as local anodes, dissolving protectively and limiting the spread of corrosion in the dendritic matrix. Subsequent heat treatment of the EBAM samples leads to the dissolution of these protective phases and structural homogenization, which causes a decrease in corrosion resistance. In contrast, hot-rolled samples demonstrate significantly higher corrosion activity. This is associated with a developed network of intergranular boundaries, which serve as paths for accelerated diffusion and centers for the development of intergranular corrosion. Selective leaching is confirmed by chromium depletion in the surface layers of the alloy. The obtained data, which establish a direct link between manufacturing technology, microstructure, and corrosion behavior, open prospects for a targeted use of additive technologies to create corrosion-resistant nickel alloys with improved performance characteristics in high-temperature aggressive media, such as halide melts.

The rapid development of femtosecond lasers facilitates the widespread use of laser technologies to solve many practical problems in such areas of material science as the development of new materials, high-precision micromachining of metals, including the process of homogeneous melting, and a number of other applications. One of the most complex physical problems has turned out to be femtosecond laser ablation, the mechanisms of which are being studied with great effort. Material research at high heating rates requires the development of new methods that are capable of tracking dynamic processes in materials with extreme spatio-temporal resolution. In this paper, a relatively simple mathematical model of the microlevel is developed to study fast interrelated processes in an overheated metastable crystal, in which a significant role belongs to the generation of structural defects. When structural defects reach certain conditions that lead to the appearance of stable nuclei of the liquid phase, the process of homogeneous melting occurs in the crystal. The determination of the main function, which is a function of the degree of crystal overheating, as well as the values of the parameters included in the proposed model, is carried out by molecular dynamics modeling of the process of homogeneous melting of a single crystal of aluminum. Using the constructed mathematical model, various crystal heating modes were investigated: with a low rate k < 100 K/ps and high values of the rate k > 100–150 K/ps. Depending on the heating rate, various lattice destruction modes are realized. In the first case, destruction occurs due to the accumulated critical number of defects. In the second, the lattice destruction is carried out due to the high kinetic energy of the particles.