Physicо-Technological Institute of Metals and Alloys of the National Academy of Sciences of Ukraine

Electrolytic processes are widely used to synthesize different nanomaterials and it does not depend on what kind of the method has been applied (wet-chemistry, sonochemistry, plasma chemistry, electrolysis and so on). Generally, the reactions in the electrolyte are considered to be reduction/oxidation (REDOX) reactions between chemical reagents or the deposition of matter on the electrodes, in line with Faraday's law. Due to the presence of electroconductive additives in any electrolyte, the polarization effect of polar molecules conducting an electrical current disappears, when external high-strength electric field is induced. Because initially of the charge transfer always belongs of electroconductive additive and it does not depend on applied voltage. The polarization of ethanol molecules has been applied to conduct an electric current by surface plasma interaction for the synthesis of a copper oxide/carbon nanocomposite material.

The concept of combined addition of C and N, as persued in previous work on martensitic steels, is transferred to austenitic stainless steels in order to gain highest phase stability. Thermodynamic calculations with special respect to the influence of temperature and interstitial content (C, N or C + N) were studied in the FeCrMnNC-system. Promising compositions like Fe-13Cr-17Mn and Fe-13Cr-21Mn revealed an extended austenitic phase field. Some appropriate alloys were investigated with regard to their microscopic and electron structure. The concentration of free electrons in the austenite as the origin of phase stabilitiy increased in the order of C, N, C + N being added. Thus, the metallic character of interatomic bonding is enhanced, which entails short range atomic order. Hence, the substitutional alloy content can be minimized. Konzept eines neuen hochfesten austenitischen nichtrostenden Stahles. Das Konzept eines C + N legierten Stahles, das bereits in früheren Arbeiten mit martensitischen Stählen untersucht wurde, soll auf austenitische nichtrostende Stähle angewendet werden mit dem Ziel eine hohe Austenitstabilität zu erreichen. Im System FeCrMnNC wurden thermodynamische Berechnungen unter Beachtung des Einflusses der Temperatur und des interstitiellen Gehaltes (C, N, C + N) durchgeführt. Erfolgversprechende Legierungen vom Typ Fe-13Cr-17Mn und Fe-13Cr-21 Mn zeigen dabei ein erweitertes Gebiet stabilen Austenits. Geeignete Stähle wurden im Hinblick auf ihre mikroskopische und Elektronenstruktur untersucht. Die Konzentration an freien Elektronen im Austenit als Ursache der Phasenstabilität nimmt in der Reihenfolge C, N, C + N zu. Dadurch wird der metallisch duktile Charakter der Bindung gestärkt, die Nahordnung nimmt zu. Die Gehalte substituierter Elemente können so minimiert werden.

Hollow graphitic carbon nanoparticles (HGCNs) obtained by catalytic graphitization of acetylene carbon black (ACB) were investigated using ultra-soft X-ray emission spectroscopy. The electronic structures of the ACB HGCNs were compared with those of HGCNs obtained from iron carbide-filled carbon nanocapsules (Fe3C@CNCs) and Q-graphenes. The occupation of the π sub-band decreased in the following sequence: Fe3C@CNC HGCNs > ACB HGCNs > Q-graphenes. This sequence can be explained by changes in the occupations of the C2p states due to the formation of bonds between carbon and residual metal atoms within the HGCNs. It was also found that the contribution of the overlapping of ppπ+ppσ-states in the ACB HGCN walls toward the spectra of the HGNCs was greater in comparison with the reference Q-graphenes. It was established that ACB was not fully transformed into the HGCNs. Scanning and transmission electron microscopy methods were used to study the spatial structures and morphologies of the fabricated HGCNs.

The results of the present study highlight the role of foaming agent and processing route in influencing the contamination of cell wall material by side products, which, in turn, affect the macroscopic mechanical response of closed-cell Al-foams. Several kinds of Al-foams have been produced with pure Al by the Alporas melt process and powder metallurgical technique, all performed either with conventional TiH2 foaming agent or CaCO3 as an alternative. Mechanical characteristics of contaminating products induced by processing additives, all of which were presented in one or another kind of Al-foam, have been determined in indentation experiments. Damage behavior of these contaminations affects the micro-mechanism of deformation and favors either plastic buckling or brittle failure of the cell walls. It is justified that there is no discrepancy between experimental values of compressive strengths for Al-foams comprising ductile Al + Al4Ca eutectic domains and those prescribed by theoretical models for closed-cell structure. However, the presence of low ductile Al + Al3Ti + Al4Ca eutectic domains and brittle particles/layers of Al3Ti, fine CaCO3/CaO particles, Al2O3 oxide network, and, especially, residues of partially reacted TiH2, results in reducing the compressive strength to values close to or even below those of open-cell foams of the same relative density.

Abstract The paper presents new method for production of closed-cell Al foams of improved sound absorbing ability with no machining operations. Opening the closed-cell structure of solid foamed Al is provided by micrometer sized cracks lengthways the eutectic domains created by finish heat treatment that includes heating below the solidus temperature followed by water quenching. The presence of through cracks provides for interconnection of the cells, making them like Helmholtz micro-perforated resonators and ensuring the increase by 15% of sound absorption coefficient. Processing parameters of foaming and followed heat treatment required for transformation of closed cells into micro-perforated resonators are discussed and specified.

The paper presents the results of the analysis of the resistance to hydrogen and high-temperature salt corrosion of the developed alloy of the CM88Y type for the turbine blades of gas turbine engines for marine and power purposes in comparison with the industrial heat-resistant corrosion-resistant alloy CM88Y and the alloy for the protective coating of the SDP3-A blades. SDP3-A alloy was chosen as a reference sample, which has high hydrogen and corrosion resistance. The new heat-resistant alloy additionally contains such refractory metals as rhenium and tantalum, which are added to the composition of the alloy in order to increase operational characteristics while maintaining phase-structural stability. These are properties such as long-term and fatigue strength, characteristics of plasticity and strength at room and elevated temperatures. Therefore, the purpose of these studies was to determine the resistance to high-temperature salt corrosion of the developed alloy in comparison with the industrial heat-resistant nickel alloy and to evaluate the influence of alloying, hydrogen embrittlement of CM88Y and ZhS3DK alloys with different contents of chromium, boron, zirconium, hafnium, and yttrium were compared. The corrosion resistance of the materials was evaluated after crucible tests in a salt solution at a temperature of 900 °C for 30 h, according to the standard method. The corrosion resistances of alloys were determined by the mass loss, corrosion rate, and data from metallographic studies.

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.

Metallic foams are commonly produced using titanium hydride as a foaming agent. Carbonates produce aluminum foam with a fine and homogenous cell structure. However, foams produced using carbonates show marked shrinkage, which is clearly different from those produced using titanium hydride. It is essential for practical applications to clarify foam shrinkage and establish a method of preventing it. In this research, cell structures were observed to study the shrinkage of aluminum foam produced using carbonates. The cells of foam produced using dolomite as a foaming agent connected to each other with maximum expansion. It was estimated that foaming gas was released through connected cells to the outside. It was assumed that cell formation at different sites is effective in preventing shrinkage induced by cell connection. The multiple additions of dolomite and magnesium carbonate, which have different decomposition temperatures, were applied. The foam in the case with multiple additions maintained a density of 0.66 up to 973 K, at which the foam produced using dolomite shrank. It was verified that the multiple additions of carbonates are effective in preventing shrinkage.

The paper presents a new method for the production of the closed-cell Al foams of improved sound absorbing ability. Final heat treatment procedure including heating below the solidus temperature followed by water quenching is proposed as an alternative method to machining, which is used commonly for improvement of the sound absorption coefficient. Several kinds of foams based on AlZnMg-alloys comprising brittle eutectic domains of interdendritic redundant phase have been produced by the Alporas-like melting process to realize the method above. Opening of the closed cell structure required for ensuring high sound absorption ability has been achieved by cracking the walls between neighboring cells, making them gas permeable. They ultimately looked like Helmholtz micro-perforated resonators. Processing parameters and other variables that are favorable both for foaming regime and for final heat treatment are discussed and specified.

The requirements for the quality and performance of the brake pads of railway rolling stock made of various materials are analyzed. The advantages of cast iron brake pads produced at foundries are shown. The disadvantages of brake pads made of composite materials based on rubber, asbestos, barite, carbon black and other components are noted. Ways to improve standards, specifications and other documentation for these products are proposed.

The phase equilibria in the ternary La2O3-Y2O3-Nd2O3 system at 1500 °C were studied by X-ray diffraction, petrography, and electron microscopy in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying, and calcination at 1100 and 1500 °C. The solid solutions based on various polymorphous forms of source components and ordered phase of LaYO3 were revealed in the system. The isothermal section of the phase diagram for the La2O3-Y2O3-Nd2O3 system has been developed. It was established that in the ternary La2O3-Y2O3-Nd2O3 system there exist fields of solid solutions based on hexagonal (A) and monoclinic (B) modifications of La2O3 and Nd2O3, cubic (C) modification of Y2O3, as well as perovskite-type structure of LaYO3 (R) with rhombic distortions. The systematic study that covered the whole composition range excluded the formation of new phases. The refined lattice parameter of the unit cell and the boundaries of the homogeneity fields for solid solutions were determined.

This paper reports a study into features of the formation of structures of permanent butt joints of plates with a thickness of 1.5 mm made from the high-strength aluminum alloy 7075 of the Al-Zn-Mg-Cu system. Welding by melting these joints was performed using three techniques: laser, microplasma, and hybrid laser-microplasma. To implement the latter two, a compressed arc on a multipolar asymmetric current was used. The purpose of the research was to establish the tendency to the formation of characteristic defects and the possibility of their elimination. It has been determined that during laser welding a small (~5 %) volumetric fraction of defects in the form of pores is formed, residual welding deformations are minimized. There is a decrease in the hardness of the melted metal by 15 % with a simultaneous increase in the hardness of the heat-affected zone (HAZ) by 8...12 % relative to the base metal. In the melted metal, cavities up to 100 μm in size are formed, which are the center of the origin of hot cracks with a length of 25‒30 μm. There are oxide inclusions in the root part of the seam. With microplasma welding, the volume fraction of defects of the melted metal in the form of pores with a size of 10...105 μm increases (up to 25 %). The hardness of the melted metal is reduced by 30 % with the hardness of the HAZ metal close to the base metal. In laser-microplasma welding, the volumetric fraction of defects of the melted metal in the form of pores with a size of 15...25 μm is reduced to 5 %. The hardness of the melted metal is reduced by 15...20 % with the hardness of the HAZ metal close to the base metal. In the lower part of the melted metal, cavities of ~100 μm are formed. No microcracks were found in the seam metal. Analysis of the research results showed the advantage of the laser-microplasma technique. This method reduces the use of laser energy by 40...50 %, the lifetime of the welding pool (0.03...0.05 s) approaches laser welding, it eliminates the danger of burnout of alloying elements.

Abstract Bismuth is a very brittle, silvery metal having a high metallic luster. It is next to lead in the periodic table of elements. Bismuth is considered nontoxic despite the fact that it has a heavy‐metal status. Bismuth is a minor metal in that it is usually mined as a by‐product and not for its own intrinsic value. It is usually a by‐product of copper or lead ores. However there are two mines that mine bismuth ore, one is in China and the other is the Tasna mine in Bolivia.The United States ceased production of bismuth in 1997. Bismuth is recovered by the Betterton‐Kroll process, Betts electrolytic process, and is recovered from tin concentrates. Bismuth has a wide variety of applications. It is used for metallurgical additives, in pharmaceuticals and in fusible alloys, solders, and ammunitions, Bismuth is used in over‐the‐counter stomach remedies and is thus considered safe. Bismuth alloys are discussed in detail.

The study presents the comparative analysis of the compressive response for the experimental aluminium foams of different parent alloys fabricated by melt processing with/without Ca additive and an expensive conventional TiH2 foaming agent or a cheap alternative CaCO3. It was recognized that the response of the foams is significantly dependent on the type of foaming agent and Ca additive due to the formation of low ductile and brittle products created in the foaming process. The presence of deformation bands and brittle eutectics in material, Al3Ti particles/layers, partially decomposed TiH2, Ca containing compounds, etc. cause a reduction of the foam’s compressive strength and deviation of its mechanical profile from the theoretical predictions. In addition, the usage of an inexpensive CaCO3 foaming agent offers numerous indisputable advantages compared to TiH2, resulting, particularly, in enhancing the energy absorption ability of foams.

The results of this study highlight the role of foaming agent and processing route in influencing the contamination of cell wall material by side products, which, in turn, affects the macroscopic mechanical response of closed-cell Al-foams. Several kinds of Al-foams have been produced with pure Al/Al-alloys by the Alporas like melt process, all performed with and without Ca additive and processed either with conventional TiH 2 foaming agent or CaCO 3 as an alternative one. Damage behavior of contaminations was believed to affect the micromechanism of foam deformation, favoring either plastic buckling or brittle failure of cell walls. No discrepancy between experimental values of compressive strengths for Al-foams comprising ductile cell wall constituents and those prescribed by theoretical models for closed-cell structure was found while the presence of low ductile and/or brittle eutectic domains and contaminations including particles/layers of Al 3 Ti, residues of partially reacted TiH 2 , and Ca bearing compounds, results in reducing the compressive strength to values close to or even below those of open-cell foams of the same relative density.

In the present investigation, the production of composites based on 7075Al is involved, reinforced with particles of high‐entropy alloy (AlCoCrFeNi), using the friction stir processing (FSP) technique. The primary objective is to examine how varying the rotational speed during processing affects the uniformity of the composite microstructure, the strength of the bonding between different materials, and the mechanical properties of the composite. In these findings, it is indicated that higher processing rotational speeds lead to enhanced homogeneity of the composite material and promote strong bonding with the matrix. The Al 13 Co 4 phase is generated at the interface before the formation of the Al 5 Co 2 phase. The microhardness of the composites exhibits an increase in hardness of 78%, 84%, 86%, and 83% compared to the hardness of the 7075Al. Similarly, the tensile strength is enhanced by 26%, 36.7%, 49%, and 40%, respectively. The broken surface shows an even spread of particles with many small depressions, which is a clear sign of a common type of fracture that can stretch without breaking. The primary processes that enhance the strength of the FeCoNiCrAl/7075Al composite manufactured by FSP include the load‐transfer effect, dispersion strengthening, grain refinement strengthening, and thermal mismatch strengthening.

By analyzing the development of standing waves and surges at the metal meniscus in the mold and their influence on crust formation, it is established that wave processes in the mold may be responsible for accidents and affect billet quality.

The expanded use of continuous-cast billet in the production of structural-steel bar is considered. The quality of 135 × 135 mm continuous-cast billet produced on a standard continuous-casting machine and the bar derived from it is evaluated. At more recently built plants, the production of quality bar from continuous- cast billet requires total extension of the order of 6–7. On the basis of the analysis developed in the present work, it is possible to determine the maximum critical bar cross section such that the required properties are ensured.

Details of a case of selective corrosion of Inconel and a tentative mechanism by which it proceeds are presented in this paper. Sheet, rod and tube samples were tested in the as-received condition by complete immersion in a fused salt bath. Tests were carried out at 800 C for tests times up to 50 days. It was found that a layer of porous sponge-like material formed on the surface. Chromium and iron were preferentially leached out of these layers. 6.3.10

Abstract Indium is a very soft, silvery metal and its abundance is about 0.05 ppm in the earth's crust. It is widely distributed, but never in concentrations high enough to justify mining for its own intrinsic value. Indium is considered a minor metal and is a by‐product of other mining and refining operations. Important mines producing indium are in South America, Canada, China, and the Republic of Korea. Indium is recovered from fumes, dusts, slags, residues, and alloys from zinc or lead‐zinc smelting. Indium metal itself poses little or no environmental risks, however sometimes the form that indium takes or other metal associated with it may pose dangers to the environment. A large portion of secondary indium is produced from indium tin oxide (ITO) recycling. Indium's major use is in the production of ITO. ITO thin film coatings are primarily used for electrically conductive purposes in a variety of flat‐panel devices. Other uses include solders and alloys, electrical components, and semiconductors.