Russian Journal of Non-Ferrous Metals最新文献

In this study, the wear performance of TiC reinforced A356 matrix composite materials produced by the mechanical alloying method at high temperatures was investigated. As a solid lubricant, 2% graphite, and four different amounts (3, 6, 9, and 12%) of TiC were added to the A356 alloy matrix. The prepared powders were mechanically alloyed in a planetary mill for 4 h. The composite powders produced were cold shaped (750 MPa) to obtain green compacts. The green compacts produced were sintered at 550°C for 60 min in a vacuum environment of 10^–6 mbar. TiC reinforced AMCs have been characterized by microstructure, hardness, and density measurements. Wear tests were carried out in a standard pin on disc type wear tester by adding a temperature module. In wear tests, two different loads (10 and 30 N), five different temperatures (20, 100, 180, 260, and 340°C), and three different sliding distances (53, 72, and 94 m) have been used. As a result of microstructure studies, it has been observed that the reinforcement material exhibits a homogeneous distribution in the structure. In hardness and density measurements, the highest hardness and density were obtained in the composite material with 12% TiC added. As a result of wear tests, the lowest weight loss was obtained in the composite material with 12% TiC added at all operating temperatures.

A comparative study of the hot deformation of the aluminum (8021) alloy with and without Sr addition under the conditions of deformation temperature of 350–500°C and strain rate of 0.01–10 s^–1 has been performed. The effect of adding 0.4% Sr on the microstructure of the alloy was investigated by EBSD and TEM, and the constitutive equations for the 8021 aluminum alloy with and without Sr were established. The results show that the hot activation energy decreases from 225.69 to 217.72 kJ/mol with the addition of 0.4% Sr to the alloy, which expands the safe processing range of the 8021 aluminum alloy. Compared with the alloy without Sr, the alloy with 0.4% Sr has a lower ln(Z) value. Adding Sr to the alloy decreases the density of dislocations, and it promotes the occurrence of dynamic recrystallization in the alloy, with an increase in the number of subgrains. The hot deformation behavior of the 8021 aluminum alloy is important for optimizing the alloy’s processing parameters and provides a reference for the industrial application of the 8021 aluminum alloy.

In this paper, titanium nitride particles (TNPs) reinforced copper-matrix graphite composites were prepared by powder metallurgy, in which copper-coated (Cu-coated) graphite (2 wt %) was used as solid lubricating phase and uncoated/Cu-coated TNPs (0, 1, 3, 5, 10, 15 wt %) was used as reinforcing phase. The effects of uncoated/Cu-coated TNPs on microstructure, density, porosity and mechanical properties of composites were studied and compared. The strengthening and wear mechanism of uncoated/Cu-coated TNPs in copper-matrix graphite composites were investigated. The results showed that electroless copper plating on the surface of TNPs can effectively improve the wettability between TNPs and copper matrix. In composites reinforced by Cu-coated TNPs, TNPs have a better interface bonding state with the matrix. Under the same content of TNPs, composites reinforced by Cu-coated TNPs have lower porosity, wear, friction coefficient, higher hardness and compressive strength than those reinforced by uncoated TNPs. TNPs can effectively strengthen the friction surface of composites. In processes of friction, TNPs will form a titanium oxide protective film on friction surfaces, which makes composites exhibit better self-lubrication, thus reducing the peeling wear. Copper plating can effectively reduce spalling of TNPs and weaken the abrasive wear and exfoliation wear of composites. Considering wear and friction coefficient, composites containing 3 wt % Cu-coated TNPs, exhibited better friction and wear resistance properties.

The use of multiple materials in the design and manufacturing of components enhances their operational characteristics. The application of additive technologies is promising for creating complex multi-material products. There are prospects for producing multi-material components from heat-resistant alloys, including nickel alloys, for the aerospace industry. The aim of this study was to investigate the influence of printing parameters using selective laser melting on the porosity and structure of bronze alloy BrKhTsrT V and VZh159, including the effect of heat treatment on the structure, chemical and phase composition, and the hardness of the transition zone in multi-materials. Multi-material samples were manufactured using an SLM 280HL selective laser melting system. Various regimes were used to study the impact of printing parameters on the porosity in the transition zone of the multi-material samples. On the basis of results of the conducted research, the following conclusions were drawn: only a significant increase in energy leads to a reduction in porosity in the transition zones of multi-material samples. Heat treatment according to regimes characteristic of the BrKhTsrT V alloy and the VZh159 alloy does not have a significant effect on the microstructure and chemical composition of the transition zones. The sizes of the transition zones were evaluated, measuring 300 µm when building the BrKhTsrT V alloy on VZh159 and 250 µm when building the VZh159 alloy on BrKhTsrT V, respectively. After heat treatment typical for each alloy, peaks corresponding to the phases of both alloys are observed in the transition zones. Different heat treatments significantly affect the microhardness of the alloys for which they are standard.

Self-dissolving medical implants, such as screws for bone fracture fixation or vascular stents, represent a promising application of magnesium alloys. Magnesium-based bioresorbable materials are currently not only the subject of research by scientific groups worldwide but also the raw material for producing commercial products—medical metallic implants that are actively used in patient treatment. Nevertheless, many technological issues remain unresolved. Chloride-containing fluxes are widely used in casting magnesium alloys. It is unclear whether the presence of flux particles in materials for bioresorbable implants poses a risk of corrosion damage to the surface of the product. This study investigates the processes of initiation and development of filiform corrosion caused by the presence of a chloride-containing particle on the metal surface. Energy-dispersive spectroscopy was used to determine the composition of corrosion products, and Kelvin probe atomic force microscopy was employed to measure their electrode potential relative to the magnesium matrix. It was shown that, under ambient temperature of 25°C and 30% humidity, filiform corrosion is initiated near the chloride-containing particle. Despite the shallow depth of damage (2–3 µm), corrosion spreads over a large area and is characterized by a high propagation rate (tens of microns per day). Analysis of the chemical composition of the corrosion products revealed that the process involves reactions leading to formation of hydroxide and its breakdown under the influence of chloride and CO₂. The corrosion products exhibit a positive potential relative to the metal, enabling the activation of anodic dissolution of the matrix. Placing the material in a vacuum completely halts progression of corrosion, which resumes upon exposure to air. This demonstrates the necessity of avoiding the use of chloride-containing fluxes in the production of bioresorbable alloys and storing finished products in a moisture-free environment whenever possible.

In this study, sulphuric acid was used to leach indium from zinc oxide dust, D2EHPA was applied to extract indium from the leaching solution, and hydrochloric acid was administered to strip indium from the indium-loaded organic phase. The effects of sulfuric acid concentration, temperature, leaching time and liquid-solid ratio on the leaching rate of indium were studied. The optimum leaching conditions for indium were as follows: sulfuric acid concentration of 200 g/L, leaching temperature of 80°C, leaching time of 120 min, and liquid-solid ratio of 8 : 1. Under these conditions, the leaching rates of indium, zinc, iron, and aluminum were 95.67, 97.97, 2.06, and 8.51%, respectively. On the contrary, lead was enriched in the leaching residue. Response surface analysis was carried out to further optimize the experimental conditions. The kinetic effects of temperature and sulphuric acid concentration on the indium leaching process were investigated using a shrinking-core model, and the activation energy of indium leaching was calculated to be 30.9 kJ/mol, with the kinetic model as: 1 – (1 – x)^1/3 = exp(5.11 – 3714/RT)t; 1 – 2x/3 – (1 – x)^2/3 = exp(8.84 + 3.599 ln[H₂SO₄])t. The results showed that the indium leaching process was controlled by a mixture of chemical reaction and diffusion, and the reaction stage of sulphuric acid was 3.599. Meanwhile, the McCabe-Thiel diagram for D2EHPA/HCl extraction/stripping of indium was constructed, and theoretically D2EHPA/HCl extraction/stripping of indium requires 2 stages to complete.

Silver extraction by percolation leaching on a pelletized sample of stale tailings with the organic binding agent Alcotac^® CB6 is studied. A column 0.5 m high and 56 mm in internal diameter was used for laboratory tests on percolation leaching. Pelletization was carried out in a drum-type granulator with the Alcotac^® CB6 reagent (BASF, Germany) consumption of 800 g/t; the moisture content of the granules was 8–10% with a size of 8–10 mm. The composition of the samples was determined based on the data of optical and electron microscopy, X-ray diffraction, local X-ray spectral, X-ray fluorescence, and mass spectrometry with inductively coupled plasma. Stale tailings of the Zhezkazgan enrichment plant (Ulytau region, Republic of Kazakhstan) were examined, in which the main part of copper is represented by oxidized minerals (78.47%); content of sulfide minerals is 21.53%. The results of physicochemical studies with the determination of the material composition of the sample and observations on the percolation leaching of copper and silver from the stale tailings of Zhezkazgan are presented. The copper leaching was studied in two stages using a sulfuric acid solution as a solvent. The next stage was the transfer of silver into the solution by cyanidation. Copper extraction into the solution was 88.55% with a sulfuric acid consumption of 80.0 kg/t of tailings, and that of silver was 75.31% with a sodium cyanide consumption of 0.55 kg/t. The studies of two-stage leaching showed the effectiveness of preliminary pelletizing of stale tailings with the Alcotac^® CB6 reagent. In the process of leaching, the pelletized material features sufficient porosity and permeability and provides access of cyanide solutions to the surface of precious metals.

Hot compression tests were conducted on an ultrahigh-alloyed Al–Zn–Mg–Cu alloy within a temperature range of 250 to 450°C and a strain rate range of 0.001 to 1 s^–1. The effects of strain rate and temperature on the flow curves were analyzed, along with the relationship between flow stress and microstructural evolution. The results indicate that, except for a strain rate of 1 s^–1 across all temperatures, the flow curves following the peak stress do not exhibit monotonic work hardening or dynamic softening. In contrast, continuous work hardening is observed at this strain rate. The diverse shapes of the flow curves are attributed to the various precipitates formed due to the high alloying element content. Dynamic recovery (DRV) is identified as the main flow softening mechanism for the ultrahigh-alloyed Al–Zn–Mg–Cu alloy. While dynamic recrystallization (DRX) contributes to flow softening at a strain rate of 0.001 s^–1, the deformed microstructure becomes the predominant softening mechanism at lower temperatures and higher strain rates. Additionally, the low intensity of isotropic texture at higher temperatures and strain rates facilitates DRX, resulting in a decrease in peak stress.