Powder Metallurgy and Metal Ceramics最新文献

An important process task is to expand the range of raw materials applied for the synthesis of dysprosium titanate (neutron-absorbing material for VVER-1000 reactors) and to establish and optimize methods for producing powders and pellets with characteristics that meet specific technical requirements, primarily those for the density and structural and phase compositions of the materials. The influence of MoO₃ doping additions and TiO₂ powders with different particle sizes on the density and phase composition of dysprosium titanate (Dy₂O₃ · TiO₂) pellets was experimentally studied. Titanium oxide powders of two grades were used: powder with spherical 10–30 μm particles (OSCh 7-3 grade as per TU 6-09-3811–79) and powder with an average particle size of ~63 nm (China Rare Metal Material Co., China). The nanosized TiO₂ powder intensified the sintering of the pellets, which achieved a density of 6.9 g/cm³ and acquired a single-phase hexagonal structure at 1650°C. The coarse TiO₂ powder did not promote high density of the sintered pellets, nor did it facilitate complete synthesis of dysprosium titanate since a significant amount of intermediate dysprosium dititanate (Dy₂Ti₂O₇) and initial dysprosium oxide (Dy₂O₃) remained in the synthesized material. The introduction of MoO₃ intensified the sintering of pellets, increased the pellet density up to 6.7 g/cm³, and led to a single-phase cubic structure of pyrochlore type, regardless of the TiO₂ powder grade. The simultaneous use of the nanosized TiO₂ powder and MoO₃ doping addition increased the density of the sintered dysprosium titanate pellets to 7.1 g/cm³ and promoted a single-phase structure of pyrochlore type.

The use of refrigeration technology is widespread in national security, industrial and agricultural production, biomedicine, and everyday life. High efficiency, environmental friendliness, and low cost make solid-state refrigeration based on electrocaloric effect (ECE) a promising refrigeration technology. Lead-free ferroelectric ceramics (1–x)Ba(Zr_0.2Ti_0.8)O₃–x(Ba_0.7Ca_0.3)TiO₃ (BZT–BCT) are promising materials for electrocaloric refrigeration in the field. In this paper, Sm-doped 0.5BZT–0.5BCT ceramic was fabricated by the conventional solid-state reaction method. The effect of Sm-doping contents (0, 1.0, 2.0, 2.5, and 3.0 mol.%) on the phase structures, dielectric properties, ferroelectricity, and electrocaloric properties of 0.5BZT–0.5BCT ceramics was systematically examined. The results indicate that all ceramics have a pure perovskite structure with no other secondary phase available. High relative densities are observed in all lead-free ferroelectric ceramics and all of the samples show transgranular fracture with no clear grain boundaries seen. The ceramics’ ferroelectric hysteresis loops become thinner as the Sm doping content increases. At that, remanent polarization Pr decreases, indicating that more polar nanoregions (PNRs) are formed in BZT–BCT lead-free ceramics through Sm doping. The increase in Sm doping content resulted in a change in the dielectric permittivity and electrocaloric temperature that first increased and then decreased. The maximum dielectric permittivity is 5,518 when the doping content of Sm is 2.5 mol.% and the maximum electrocaloric temperature change ΔT_max of 0.109 K at 4 kV/mm was obtained when Sm doping content was 2 mol.%. The results show that an appropriate Sm doping is favorable for improving the dielectric, ferroelectric, and electrothermal properties of lead-free ceramics 0.5BZT–0.5BCT.

Aluminum metal matrix composites (AMMCs) are a new modern group of composite materials that are becoming more popular in industrial progress. As a solid welding method to fabricate metal matrix composites, accumulative press bonding (APB) is one of the most capable processes. One of the major disadvantages of the APB process is the weak bonding strength. This study utilizes tin (Sn) particles as filler metal to enhance the bonding strength of aluminum laminates. Thus, AA1060 bars with different content of Sn particles (interlayer filler material) were manufactured at various pressing temperatures and APB steps. The peeling test was used to evaluate the bonding strength. It was found that by increasing the number of APB steps, Sn content, and pressing temperature, better bonds of higher strength and quality were generated. The bonding strength was improved to 424 N for a sample fabricated with 15 wt.% of Sn particles at 300°C. Scanning electron microscopy (SEM) was used to examine the peeling surface of Al/Sn composite samples.

Buildup (or additive manufacturing) processes enable the production of components where individual sections can possess distinct chemical compositions tailored to their specific purpose. However, the distribution of elements in the fusion zone and its sizes remain inadequately understood. Samples of VT1-0 and VT20 titanium alloys were fused so that the VT1-0 alloy powder was deposited onto the VT20 cast alloy in one case and the VT20 titanium alloy powder was deposited onto the VT1-0 cast alloy in the other. Regardless of the grain-size and chemical compositions of the powders, the chemical composition of the samples met relevant standards for the alloys. The macrostructures were studied employing a Neophot 32 optical microscope. Minimal porosity was revealed in the samples across all deposition options. Microstructural analysis showed that the deposited material formed a uniform structure both longitudinally and transversely. The microstructure in zones with specific chemical compositions resembled that of the associated as-cast alloys. Variations in the sizes and shapes of structural components were observed toward the powder/cast metal fusion line. A distinct transition zone was found in the fusion of titanium alloys with different chemical compositions. The chemical composition in the longitudinal and transverse sections in the powder/cast metal fusion zone was examined with a scanning electron microscope. The chemical composition was established at different distances from the fusion line. The results showed that the chemical elements redistributed and their contents changed. The presence of zones with altered chemical composition was ascertained by microstructural studies. The distribution of chemical elements was qualitatively assessed and found to be uniform.

To select and optimize the experimental conditions for producing powders from wear-resistant cobalt alloys, the following methods were tested: gas spraying of the KhTN-37 alloy, centrifugal spraying of the KhTN-61 alloy, cryogenic spraying of the KhTN-61 alloy, and ultrasonic plasma atomization of the KhTN-62 alloy melt. The production of particles in different sizes and shapes, the difference between the experimental values of their sizes, and the potential of using individual size fractions taking into account the industrial production requirements were analyzed and summarized. The gas spraying method used for the KhTN-37 alloy did not yield the required amount of suitable powder and was thus inexpedient. The centrifugal spraying method for the production of KhTN-61 alloy powders was characterized by a significant number of spherical/needle particles formed in the sprayed material, affecting its flowability and complicating sieving. In addition, this method did not reliably protect the sprayed material against oxygen. The cryogenic spraying process for producing KhTN-61 alloy powders turned out to be unsuitable because it changed the chemical composition. The method involving melt ultrasonic atomization turned out to be the most acceptable for producing KhTN-62 alloy powders. It yielded a fine spherical powder with the required particle size. The use of this rapidly hardened powder is promising for the development of wear- and oxidation-resistant surface layers on responsible components of friction units in power equipment, particularly in aircraft structures. The high-temperature wear-resistant alloy powders can be recommended for strengthening and restoring the surfaces of components in friction units in aviation equipment and for additive manufacturing of bulk parts (3D printing), possessing high wear resistance at elevated temperatures.

A comparative study of the structure and properties of composite materials produced from biogenic hydroxyapatite/glass/carbon fibers, depending on the type of carbon fibers (activated carbon nanostructured fibers or cellulose fibers), was conducted employing scanning electron microscopy, X-ray diffraction, infrared spectroscopy, Brunauer–Emmett–Teller method, helium pycnometry, and in vitro experiments. The potential to produce a biogenic hydroxyapatite/glass/carbon fiber composite by sintering at 800°C, involving the simultaneous formation of carbon nanostructures during thermal destruction and carbonization of cellulose fibers, was ascertained. This method allows preserving the hydroxyapatite phase in the newly formed biogenic hydroxyapatite/glass/carbon fiber composite and ensures the presence of carbon nanostructures. The microstructure of the composites produced with activated carbon nanostructured fibers is characterized by the presence of these fibers, contrastingly to the composite produced with cellulose fibers, which has more homogeneous microstructure. Moreover, as opposed to cellulose fibers, activated carbon nanostructured fibers in the composite significantly increase (by more than three times) the specific surface area of the material and significantly reduce the particle size. Regardless of the carbon fibers used, the biogenic hydroxyapatite/glass/carbon fiber composites are nanostructured and microporous (pores < 2 nm). The resorption rate of the biogenic hydroxyapatite/glass/carbon (activated nanostructured or hydrated cellulose) fiber composites in the physiological solution within the first two days is significantly higher than that of the starting biogenic hydroxyapatite/glass composites because of changes in the porous structure.

The interaction of Sc₂Ni₇ and Zr₂Ni₇ compounds (with C2/m and P6₃/mmc crystal structures and congruent melting temperatures of 1270 and 1438°C) in the ternary Ni–Sc–Zr system was studied employing physicochemical analysis methods (metallography, X-ray diffraction, differential thermal analysis, and electron microprobe analysis). The section between the compounds was shown to be quasibinary of peritectic type, with peritectic points of 1340 ± 13°C and 14 at.% Sc. At the peritectic temperature, about 10 at.% Zr dissolves in the Sc₂Ni₇-based phase and about 8 at.% Sc in the Zr₂Ni₇-based phase. Electrochemical studies conducted through cathodic polarization of the ternary Sc₂Ni₇ and Zr₂Ni₇ alloys using a PI-50-1 potentiostat, with a three-electrode electrochemical cell consisting of a working ceramic anode, a platinum cathode, an electrolyte (a 3% NaCl aqueous solution), and a silver chloride Ag/AgCl/KCl reference electrode, did not reveal any tendency to hydrogenation in their solid solutions. The influence of preliminary cathodic reduction of the 77.8 at.% Ni–8 at.% Sc–Zr sample on its subsequent anodic dissolution was determined. The initial surface of the 77.8 at.% Ni–8 at.% Sc–Zr sample was found to be much more resistant to anodic oxidation than the surface preliminary subjected to cathodic reduction because of a significant decrease in its oxide component.

Two typical microstructures of Ti–6.6Al–1.7Mo–2.3V–1.9Zr (TA15) titanium alloy were successfully fabricated by vacuum hot pressing using TA15 metallic powders of two different sizes with the spherical shape of particles. The size of prior β grains was consistent with the size of the as-received TA15 alloy powder. The microstructure of TA15 alloys differed depending on the size of the initial powder, forming Widmanstätten patterns for the sample from coarse powder or equiaxed microstructure for fine powder. The microstructure evolution during the vacuum hot pressing included solid-state phase transition and powder compact. In the temperature-rise period, the solid-state phase transition occurred (α → β). The anterior β-grain only grew to the original powder interface, which means that it would not coarsen causing its size to exceed that of the original powder. The solid-state phase transition occurred (β → α) when the temperature decreased during the subsequent cooling process. The nuclei of grain boundaries α appeared at the grain boundary of the anterior β-grain. Then the nuclei of grain boundaries α grew together enclosing the anterior β-grain. The grain boundaries α belonged to a certain anterior β-grain and could provide nucleation sites for the α-colonies of the two adjacent anterior β-grains. Finally, the α colonies grew into the anterior β-grain forming the Widmanstätten structure. The two typical microstructures will likely affect the mechanical properties of the TA15 alloys. An improvement in tensile properties was evident in the TA15 alloys (equiaxed microstructure) fabricated from a fine powder compared to their predecessors, consisting of colonies α microstructure fabricated from the coarse powder. To be specific, the tensile strength increased from 849 to 898 MPa and the ductility growth was from 5.5 to 6.5%.

The production of intricate samples from polymer–ceramic composites employing fused deposition modeling was studied. The samples were subjected to high-temperature heat treatment in microwave furnaces to yield titanium nitride ceramics. The conditions for making polymer–ceramic materials from polypropylene and titanium nitride powders and 3D printing conditions for associated intricate parts were examined. The TiN–polypropylene composite was produced at a temperature of 190°C through extrusion of a previously prepared homogeneous mixture with a reinforcement content of 10, 20, 40, 46, 50, and 60 vol.% TiN. Using fused deposition modeling, a gear-shaped part made of the polymer–ceramic material was printed. The printed samples with 20 and 40 vol.% TiN were heat-treated in microwave furnaces in air in a carbon black backfill and in a nitrogen flow. Following the heat treatment in microwave furnaces, the samples preserved their initial shape. The composite samples treated in a carbon black backfill in air exhibited a porosity of ~38% and those treated in a nitrogen flow showed a porosity of ~22%. The samples subjected to microwave heat treatment in a carbon black backfill in air underwent sintering and partial oxidation. After microwave heat treatment in a nitrogen flow, the titanium nitride samples showed higher density and bimodal structure with titanium nitride grains varying from several micrometers to 400–200 nm. The microhardness of the samples heat-treated in a carbon black backfill was 6.5–8.5 GPa and that of the samples treated in a nitrogen flow was 16 GPa.

The potential of wastewaters from the galvanic industry treated to remove toxic heavy-metal contaminants for the manufacture of commercial products lies in the development of processes for their reuse. This research addresses the feasibility of employing galvanic waste in the production of powder coatings. Powder waste generated through the resource-saving ferritic method and electroerosion dispersion method is significantly safer for the environment than that generated through reagent methods. Coatings resulting from wastewater treatment exhibit mechanical properties that meet current industry standards. The introduction of 15 wt.% spent polyvalent iron oxide sorbent into paint coatings enhances their mechanical performances. Specifically, the rebound strength increases from 20 to 40 cm/kg and tensile strength from 5 to 7.4 mm, the bending strength decreases from 8 to 5 mm, and the corrosion resistance of the coatings improves by 1.5 times compared to the standard samples. These improvements are attributed to the introduction of chemically and thermally stable crystalline phases possessing ferromagnetic properties into the coatings. As a result, these coatings increase shielding against electromagnetic radiation in the megahertz range by three times compared to the standard coatings. A significant research finding is the potential for reusing ferromagnetic waste from the galvanic industry in specialized materials.