Fine-grained Powder Research Articles

Influence of Processing Routes to Enhance the Mechanical Properties of Mg–6Zn–1Y–3.5CeMM (wt.%) Alloy

The microstructure and mechanical properties were investigated for Mg–6Zn–1Y–3.5CeMM (wt.%) alloy processed by extrusion at 400 °C of as-cast ingots (ACE alloy) or cold-compacted atomized powders (PME alloy). The use of fine-grained atomized powders results in a refinement of the microstructure, manifested by a reduced grain size and a smaller particle size with respect to the alloy processed by casting. The second-phase particles are the same for both W-phase (Mg3Zn3Y2) and T-phase (MgZnCeMM compound) particles, regardless of the processing route. The yield stress of the PME alloy at room temperature is not only increased by almost 40% compared with that of the ACE alloy (307 and 224 MPa, respectively), but the elongation to failure also increases to twice as much for the PME alloy. This differing mechanical behavior is related to the smaller grain size and the homogeneous distribution of the second-phase particles in the PME alloy. Up to 200 °C, both alloys maintain high mechanical strength, with UTS values remaining above 120 MPa. At high temperatures and low strain rates, deformation is controlled by grain boundary sliding, improving the ductility at the expense of a significant decrease in the yield strength of the ACE and PME alloys.

Asbestos Hazard in Serpentinite Rocks: Influence of Mineralogical and Structural Characteristics on Fiber Potential Release

Naturally occurring asbestos (NOA) represents a matter of social and environmental concern due to its potential release in the atmosphere during rock excavation and grinding in quarry and road tunnel activities. In most cases, NOA occurs in serpentinites, i.e., rocks deriving from low-grade metamorphic hydration of mantle peridotites. The potential release of asbestos fibers from serpentinite outcrops depends on several features, such as serpentinization degree, rock deformation, weathering, and abundance of fibrous veins. In this study, we selected a set of serpentinite samples from a representative outcrop in Tuscany (Italy), and we analyzed them by Optical, Scanning, and Transmission Electron Microscopies. The samples were treated by grinding tests following the Italian guidelines Decrees 14/5/96 and 152/2006 for the determination of the Release Index (RI), i.e., the fiber amount released through controlled crushing tests. The fine-grained powder released during the tests was analyzed by quantitative Fourier transform infrared spectroscopy (FTIR) to determine the variety and the amount of released fibers and to assess the potential hazard of the different serpentinite samples. Results indicate that the amount of released fibers is mostly related to serpentinite deformation, with the highest RI values for cataclastic and foliated samples, typically characterized by widespread occurrence of fibrous veins. Conversely, massive pseudomorphic serpentinite revealed a very low RI, even if their actual chrysotile content is up to 20–25%. Based on our original findings from the RI results, a preliminary investigation of the outcrop at the mesoscale would be of primary importance to obtain a reliable hazard assessment of NOA sites, allowing the primary distinction among the different serpentinites lithotypes and the effective fiber release.

Proportioning of Oil Shale Ash for Sustainable 3D Printable Mortars

To achieve optimal strength and printability, mortars used in 3D printing typically contain high proportions of cement and other fine-grained powders. Consequently, the majority of mixtures used in 3D printing have high carbon footprint. Hence, there arises a critical need to study alternative supplementary cementitious materials aimed at reducing the environmental impact of mortars used in 3D printing. The use of oil shale ash as a partial substitute for cement not only addresses this issue but also presents an opportunity to repurpose waste from power plants in the Baltic states, where oil shale is intensively utilized.In this study, the influence on mechanical properties and durability of cement-based mortars was evaluated by substituting cement with oil shale ash in varying quantities. Specifically, 0% to 40% of cement mass was replaced with oil shale ash. Life cycle assessment (LCA) was performed for each mixture. By analyzing the material properties alongside the environmental impact for each mixture, the optimal percentage of substitute was determined.For the determination of the mechanical properties of each mixture, compressive and flexural strength tests were conducted on 3D printed samples in various directions, as well as on cast samples. To assess the durability of each mixture, freeze-thaw tests were performed on both 3D printed and cast samples.From the obtained results, we developed an algorithm that chooses the optimal mixture proportioning. Depending on material performance requirements set in the beginning, this algorithm gives the exact proportions of oil-shale ash and cement for the mixture, by taking into account both desired material properties and carbon dioxide emissions. As a result, an environmentally friendly cement-based mixture is obtained without losing the desired properties. By using this algorithm, it is possible to create a mortar with properties comparable to concrete with strength class C30/37 while reducing carbon emissions by 15% to 30%.

Nanosized Tungsten Powder Synthesized Using the Nitridation–Decomposition Method

A facile, one-step nitridation–decomposition method was developed for the synthesis of nanosized tungsten powder with a high surface area. This approach involved the nitridation of WO3 in NH3 to form mesoporous tungsten nitride (W2N), followed by in situ decomposition of W2N to directly yield single-phase W particles. The phase and morphology evolution during the synthesis were systematically investigated and compared with the carbothermal reduction of WO3. It was revealed that powdered tungsten product with single-phase particles was obtained after nitridation at 800 °C combined with in situ decomposition at 1000 °C, displaying an average particle size of 15 nm and a large specific surface area of 6.52 m2/g. Furthermore, the proposed method avoided the limitations associated with intermediate phase formation and coarsening observed in carbothermal reduction, which resulted in the growth of W particles up to ~4.4 μm in size. This work demonstrates the potential of the nitridation–decomposition approach for the scalable and efficient synthesis of high-quality, fine-grained tungsten powder.

High-strength 91W-6Ni-2Co-1Fe tungsten heavy alloys prepared by laser melting deposition using granulated powder

This study introduces a new approach for fabricating high-strength 91W-6Ni-2Co-1Fe tungsten heavy alloys (WHAs) using laser melting deposition (LMD) with a specially formulated granulated powder, characterized by near-spherical particles and a dense structure with fine W grains (2.6 μm). Thin plate samples were prepared using laser powers from 500 W to 900 W, revealing increased density at higher laser power, while the W grain size remains relatively stable. A near-fully dense sample (99% density) with the finest W grain size of 2.8 μm is obtained at a laser power of 900 W, while the highest hardness of 482 HV is achieved at 700 W. The contributions of the high cooling rate of LMD, the Co addition, as well as the use of fine-grained granulated powder to enhance the high strength are discussed. These findings offer significant insights into optimizing WHA fabrication using LMD, highlighting its potential in advanced materials engineering.

Enzyme Preparation Characteristics and New Technical Solution Development for Bioconversion of Collagen-Containing Raw Materials

One of the modern challenges facing the food and processing industry is the rational and resource saving technology development for the secondary resources use including collagen containing raw materials. Raw materials bioconversion is a promising solution method for the problem. A man run the research on the enzyme preparation use as hydrolysates of food raw materials including for the meat processing industry; studied the technological solutions appeared in the scientific and technical literature; identified the strengths and weaknesses of hydrolysis methods. Based on the studied data, the authors developed technological approach to the bioconversion of the broiler chicken skin. The developed approach consists in the technological preparation of collagen containing raw materials, its grinding, processing with an enzyme preparation from secondary fish raw materials for 15 minutes at a temperature of (3 ± 2)°C in a refrigerating chamber followed by filtration, regrinding and drying at a temperature of (41 ± 2) °C. According to the results of the conducted studies, the enzyme preparation is capable of collagen compound hydrolyzing, the proteolytic activity is 2.9 U/g. The enzyme preparation is a light-yellow substance with a faint specific aroma, a liquid, slightly viscous consistency. The mass fraction of dry substances in the enzyme preparation is 44%, the mass fraction of protein is 15%. Broiler chicken skin processing with an enzyme preparation resulted in a fine-grained free-running powder of light-yellow color with a mass fraction of 81.1% protein, 14.2% fat, 4.7% moisture, and 64.4% collagen. The ways of using the obtained collagen fermentolysate have been determined. The developed technology of using broiler chicken skin treated with an enzyme preparation is a new modern technical solution in the bioconversion of collagen containing raw materials. A man can exploit it in the food technology of meat pates and minced meat.

Perfectly dense ceramics of highly pure calcium manganese oxide

Immensely thermally stable and perfectly dense ceramics of highly pure calcium manganese oxide (CaMnO3) powders is realized at optimized minimal processing temperature and time using cost-effective ball-milling and hot-press techniques. The effect of ball milling time on the calcination time to prepare highly pure CaMnO3 powder and sintering time on the temperature adequate enough to achieve perfectly dense CaMnO3 ceramics is studied thoroughly and systematically. The as-synthesized single phase CaMnO3 is attained by mixing precursors of calcium carbonate and manganese oxide, using high energy ball milling for longer time followed by calcination for shorter time duration and vice-versa. A decrease in particle size in as-synthesized CaMnO3 is noticed for powders prepared with longer ball milling and shorter calcination times. The minimal time required for achieving highly pure and fine-grained powders containing sub-micrometer particles of CaMnO3 is accomplished by ball milling the precursor mixture for 12 h and calcining at 1273 K for 2 h. Relative density of 99.03% is achieved for the as-synthesized CaMnO3 powders hot pressed at 1073 K for 30 min.

Preparation and properties of shape-stable phase change material with enhanced thermal conductivity based on SiC porous ceramic carrier made of iron tailings

SiC porous ceramic carriers with adjustable porosity of 79.9%–90.7% were prepared by foam gel-casting forming and carbothermal reduction reaction sintering, using industrial waste fine-grained iron tailings and graphite powder as raw materials. Then paraffin/SiC shape-stable phase change materials were prepared by spontaneous infiltration employing paraffin as phase change material. Thermal conductivity of the SiC carriers (0.17–0.31 W/m·K) is 2.7–3.7 times higher than that of iron tailings porous ceramics with the same porosity. A thermal conductivity model of the SiC carrier is established and verified by experimental data. Phase composition, microstructure, molecular structure, mechanical properties and thermal properties of the shape-stable phase change materials were characterized by XRD, SEM, FT-IR, WDW, Hot Disk and DSC, respectively. There is only a physical combination between paraffin and SiC carriers. The compressive strength of the shape-stable phase change materials (2.0–2.3 MPa), weight loss and latent heat loss are less than 5% and 4.7% after 100 thermal cycles, respectively, which can meet the application requirements as a functional material. Thermal conductivity of the shape-stable phase change materials (0.7–0.73 W/m·K) is significantly improved, a latent heat of 138.5 J/g, and the efficiency of energy storage and release is 2.3–3.3 times as good as than that of paraffin, suggesting that this material is capable of recycling and reusing waste heat as a highly efficient thermal energy storage system.

Grain Size Effects on UV–MIR (0.2–14 μm) Spectra of Carbonaceous Chondrite Groups

Carbonaceous chondrites are among the most important meteorite types and have played a vital role in deciphering the origin and evolution of our solar system. They have been linked to low-albedo C-type asteroids, but due to subdued absorption bands, definitive asteroid–meteorite linkages remain elusive. A majority of these existing linkages rely on fine-grained (typically < 45 μm) powders across a limited wavelength range in the visible to near-infrared (0.35–2.5 μm). While this is useful in interpreting the fine-grained regolith of larger main-belt objects like Ceres, recent spacecraft missions to smaller near-Earth asteroids (NEAs), such as Bennu and Ryugu, have shown that their surfaces are dominated by larger grain size material. To better interpret the surfaces of these smaller, carbonaceous NEAs, we obtained laboratory reflectance spectra of seven carbonaceous chondrite meteorite groups (CI, CM, CO, CV, CR, CK, C2-ungrouped) over the ultraviolet to mid-infrared range (0.2–14 μm). Each meteorite contained five grain size bins (45–1000 μm) to help constrain spectral grain size effects. We find a correlation between grain size and absolute reflectance, spectral slope, band depth, and the Christiansen feature band center. Principal component analysis of grain size variation illustrates a similar trend to lunar-style space weathering. We also show that the Bus–DeMeo asteroid taxonomic classification of our samples is affected by grain size, specifically shifting CM2 Aguas Zarcas from a Ch-type to B-type with increasing grain size. This has implications for the parent body of the OSIRIS-REx target, Bennu. With Aguas Zarcas, we present results from Hapke modeling.

Characterization and Magnetic Properties of Sintered Glass-Ceramics from Dispersed Fly Ash Microspheres

The recycling of hazardous industrial waste into high-tech materials with desired properties is of considerable interest since it provides optimal alternatives for its final disposal. Coal fly ash, the major waste generated by coal-fired power plants, contains significant quantities of dispersed microspheres with a diameter smaller than 10 μm, which are anthropogenic atmospheric pollutants PM10. Due to their composition and fine-grained powder morphology, they can be converted into sintered products. In this study, dispersed microspheres from class C fly ash were directly sintered without any additive to form high-strength glass-ceramics with magnetic properties. The optimum processing conditions were achieved at a temperature of 1200 °C, at which samples with a compressive strength of 100.6 MPa were obtained. Sintering reduces the quantity of the glass phase and promotes the formation of larnite, Fe-spinel, ye’elimite, and ternesite. Mössbauer measurements show that the relative concentration of the magnetic phase compared to the paramagnetic one rises almost in order. The sintered sample demonstrates a narrower distribution of the hyperfine magnetic field and a significantly lower value of the coercive field of 25 Oe, which allows proposing such materials as soft magnetic materials. The presented results demonstrate promising industrial applications of hazardous PM10 to minimize solid waste pollution.

Effect of the Particle Size Distribution of Irregular Al Powder on Properties of Parts for Electronics Fabricated by Binder Jetting

The present work analyzed the influence of the particle size of irregular aluminum powder on the properties of Binder-Jetting-printed parts, which can be used as electronic components. Powders of various particle sizes as well as blends in the ratio of 73–27 wt.% or 27–73 wt.% of coarse to fine powder particles were used. The parts were printed with constant parameters, such as a layer thickness of 120 µm, roller traverse speed of 10 mm/s, and binder saturation of 80%. For parts made of individual blends, analysis of the XRD, density, porosity, surface roughness, and dimensional changes in X, Y, and Z axes after the sintering process was conducted. The results confirmed the trend of smoothing the surface of 3D-printed parts with a reduction in the size of the powder particles used. The best results in terms of surface roughness were obtained for powder in which coarse particles (73%) had 50 µm and fine particles (27%) had 20 µm. However, the incorporation of coarser particles in an amount of 27 wt.% (AL160) to the fine-grained powder base (ALC100) allowed for the obtaining of details with higher density, lower total porosity, and relatively low surface roughness. The combination of these two powder particle sizes allowed the fine powder to fill the voids between the larger particles, resulting in properties that represent an excellent relationship between density, porosity, and surface quality. The research results indicate that the three-dimensional parts produced by Binder Jetting technology, through the phenomenal thermal conductivity of aluminum, can be successfully used as electronic components, such as heat sinks or transistor housings.

Clay/nanocomposite hydrogels: In review

The development of advanced materials those are stronger, more rigid, lighter, hotter and self-renewable than existing materials has been the rising point of many research studies conducted in recent years. Within this scope, the interest to production of nanostructured materials is received considerable attention worldwide due to their potential positive contribution to wide variety of technological areas such as electronics, catalysis, adsorbents, ceramics, magnetic data storage, structural components etc. In these efforts polymer nanocomposites as the form of hydrogels, reinforced with well-dispersed layered silicate, typically montmorillonite can be given as a one of the promising composite material. However, long-standing problems for polymer-clay nanocomposites include actual exfoliation of clay particles in discrete layers, uniform distribution of clay layers throughout the polymer, and randomness of clay sequences. For the exfoliation of clay particles, although the chemical modification of clay minerals in aqueous media is the well-known and more general way applied by researchers, the physical pathway method performed by high-energy ball mills is also gaining increasing attention as an alternative pretreatment way. Grinding of crushed materials is one of the key processes in the mineral and cement industry, but the increased concern on the preparation of fine-grained powders (nano powders) or the manufacture of composites with desirable properties, especially performed with use of high-energy ball mills, has led to significantly widen the usage field of grinding. Undoubtedly, the main reason for these efforts is to improve the performance of existing materials. In this paper the fundamental concepts, classification, physical and chemical characteristics and the production methods of clay/polymer nanocomposites was briefly reviewed base on the composite hydrogel. Particular attention was paid to the pre-treatment (exfoliation) of clays with high-energy ball mills, which is increasingly being accepted as an alternative method to eliminate the negative effects of chemical treatment in some composite forms.

Influence of Sodium Hexametaphosphate on Muscovite Grinding and Its Mechanism Analysis

In this paper, different doses of sodium hexametaphosphate (SHMP) were added as grinding aids in the process of muscovite grinding, and the effect of SHMP on the grinding efficiency of muscovite was studied. The grinding experiment results show that the grinding efficiency increases significantly with the increase in SHMP dosage. The mechanism of SHMP improving the grinding efficiency of muscovite was analyzed by various test methods. Experimental results showed that when SHMP was used as a grinding aid, the ordered structure of muscovite crystals was destroyed, the surface of muscovite was roughened, and obvious cracks appeared. SHMP was physically adsorbed on the muscovite powder, which effectively improved the pulp environment of muscovite powder during grinding, resulting in more dispersed muscovite powder, and improved the grinding efficiency. This study provides theoretical guidance for the efficient preparation of fine-grained muscovite powder and the action mechanism of grinding aids.

Creation of self-hardening aluminum phosphate binders for manufacturing foundry cores

The aims of this publication is to study the physical and chemical conditions of formation of self-hardening aluminum phosphate binders based on orthophosphoric acid and fine-grained aluminum powder, research of its chemical structure and properties of core mixtures for foundry production.The methods used in the work are: X-ray phase analysis on the Rigaku Ultima IV, differential thermogravimetric analysis on the STA 449 C. Orthophosphoric acid 85% concentration and finely dispersed aluminum powder were used as materials. Samples of core mixtures were made on the basis of quartz sand with an average particle size of 0.2 … 0.3 mm.As a result of the experiments, it was established that in the system of orthophosphoric acid and finely dispersed aluminum powder, a chemical interaction occurs at ambient temperature, which leads to the formation of a phosphate binder. It has been confirmed that it is aluminum orthophosphate in the form of berlinite, and it does not undergo phase transformations, namely it is thermally stable when heated from 20 to 1000 оС. A significant advantage for core mixtures in foundry production is that the chemical interaction in this system does not begin immediately after mixing the components, but after 5 … 10 min, which is explained by the presence of protective oxide or hydroxide films on the aluminum particles. This ensures the period of technological suitability of the core mixture, and subsequently ensures its self-hardening.In contrast to previously known aluminum phosphate binders, which required heating from 200 to 300 оС for their hardening, a self-hardening aluminum phosphate binders and the core mixture based on it were created for the first time.With the amount of 2 … 3% of orthophosphoric acid and 1 … 2% of aluminum powder, after 1 h the strength indicators of the mixture based on quartz sand exceed 1 MPa, which is sufficient for the production of foundry cores.

Tensile properties and deformation behavior of an extra-low interstitial fine-grained powder metallurgy near alpha titanium alloy by recycling coarse pre-alloyed powder

An extra-low interstitial near alpha alloy Ti−3Al−2Zr−2Mo (wt%) was fabricated by hydrogenation and thermomechanical consolidation (TMC) of the coarse and spherical pre-alloyed powder with particle sizes of 60 to 270 μm. The coarse powder is a byproduct of pre-alloyed powder produced for selective laser and electron beam additive manufacturing. The TMC process involves powder compaction, fast sintering, in-situ dehydrogenation and an immediate hot extrusion to form a fully dense and fine-grained martensitic microstructure. Further dehydrogenation in vaccum at 700 °C converted the martensitic microstructure into an interwoven α/β microstructure which exhibited an improved yield strength, apparent necking and premature cracking at grain boundary α (αGB) ribbons. A further annealing of 880 °C/1 h/AC led to the formation of a fine-grained α/βt composite structure, which achieved an enhance ultimate tensile strength of 835 MPa and excellent tensile ductility of 16.0%. Analysis of the deformation behavior of the alloy in different states revealed that the α/βt composite structures brought about an enhanced strain hardening capability by heterogeneous deformation effect of hard βt and soft α-laths, which inhibited the formation of microcracks and consequently improved the coordinated deformation.

Fabrication of dense albite aggregates by hot pressing

Synthetic rocks are used in laboratories to measure the physical and chemical properties of Earth’s constituent minerals in order to understand Earth’s interior. To understand the phenomena in the middle and upper crust, dense aggregates of Na-rich plagioclase are necessary. Therefore, we explored a method of fabricating dense aggregates of albite with low porosities, homogeneous microstructures, the absence of melt and sample sizes larger than a cubic centimetre using hot pressing by solid-state sintering. We conducted multiple experiments in which we varied the particle sizes, the agglomerations of powder, the method of forming, the sintering temperature, and the pressure and duration of the hot pressing. Two particle size fractions of powder, less than two micrometres and less than a few hundred nanometres, were prepared by pulverisation and decantation of natural albite powder. Because fine-grained albite powder seems to agglomerate easily, a technique to dry and disperse the powder was also developed. Hot pressing was carried out at temperatures of 1000‒1150 °C and pressures of 40‒120 MPa. The following were found to be important in obtaining dense aggregates of albite: (1) powders with a particle size less than a few hundred nanometres; (2) powders are adequately dispersed; and (3) preparation of green bodies by slip casting, which makes hot pressing efficient. A dense albite aggregate can then be fabricated using hot pressing at a temperature of 1080 °C and pressure of 100 MPa by solid-state sintering.

Effect of grain boundary state and grain size on the microstructure and mechanical properties of alumina obtained by SPS: A case of the amorphous layer on particle surface

The work was aimed at the investigation of kinetics of Spark Plasma Sintering (SPS) of the α-Al2O3 particles with amorphous surface layers and investigation of the effect of the amorphous layers on the grain growth and on the mechanical properties of alumina. The objects of investigations comprised:(i) submicron α-Al2O3 powder, (ii) submicron α-Al2O3 powder with the amorphous layers on the particles' surfaces, and (iii) the fine-grained α-Al2O3 powder. The submicron powders (i) and (ii) were used to analyze the effect of the amorphous layers on the sintering kinetics. Powders (i) and (iii) were used to analyze the effect of the initial particle sizes on the shrinkage kinetics. The effect of the temperature regime and of the rate (Vh) on the shrinkage kinetics of the submicron and fine alumina powders has been studied. The shrinkage curves were analyzed using the Young–Cutler and Coble models. The sintering kinetics was shown to be determined by the intensity of grain boundary diffusion for the submicron powders and by simultaneous lattice diffusion and grain boundary one for the fine powders. The amorphous layers on the surfaces of the submicron α-Al2O3 particles were found to affect the grain boundary migration rate and the Coble equation parameters at the final stages of SPS. The abnormal characteristics of the alumina ceramics sintered from the submicron powder with the amorphous layers on the particles’ surfaces were suggested to originate from the increased concentration of the defects and of the excess free volume at the grain boundaries formed during crystallization of the amorphous layers.

An Electrochemical Sensor Based on Carbon Paper Modified with Graphite Powder for Sensitive Determination of Sunset Yellow and Tartrazine in Drinks.

The paper describes the development of an electrochemical sensor to be used for the determination of synthetic food colorants such as Sunset Yellow FCF (SY) and Tartrazine (TZ). The sensor is a carbon paper (CP) electrode, manufactured by using hot lamination technology and volume modified with fine-grained graphite powder (GrP). The sensor (GrP/CP) was characterized by scanning electron microscopy, energy dispersive spectrometry, electrochemical impedance analysis, cyclic, linear sweep and differential pulse voltammetry. The mechanism of SY and TZ electrochemical oxidation on GrP/CP was studied. The developed sensor has good electron transfer characteristics and low electron resistance, high sensitivity and selectivity. Applying the differential pulse mode, linear dynamic ranges of 0.005–1.0 μM and 0.02–7.5 μM with limits of detection of 0.78 nM and 8.2 nM for SY and TZ, respectively, were obtained. The sensor was used to detect SY and TZ in non-alcoholic and alcoholic drinks. The results obtained from drink analysis prove good reproducibility (RSD ≤ 0.072) and accuracy (recovery 96–104%).

Additive manufacturing parts made of cobalt-chromium powders synthesized by electroerosion dispersion

Considering the standard procedure for producing globular powder particles, the authors of this paper propose to use the process of electroerosion dispersion for the production of globular particles of certain size for 3D technology. The proposed process is characterized with energy efficiency and sustainability. The waste cobalt-chromium alloy of the TsELLIT grade was used for the purposes of the study. Cobalt-chromium powders were produced by electroerosion dispersion on a special unit designed for conductive materials. Through experiments, it was established that as the particle dispersion rises, the baking process goes faster resulting in enhanced mechanical properties of the final products. Oxides present in fine-grained powders contribute to the intensity of the baking process as they are subject to reduction under heat impact. The spongy texture that forms when the oxides are gone from the metal surface appears to be more active compared with the oxide-film-free surface. The conducted study showed no changes to the structural and phase state of the specimens. Hence, all four specimens retained the following phases: Co, Cr, Ni и Cr3Ni2. The increasing dispersion and specific surface area of the powder leads to decreased porosity and increased microhardness in the final product. Due to the presence of particles of various sizes, the powder layer appears to be denser as cavities and micropores occurring between coarser particles get filled up. This results in lower roughness and higher compression and bend strength in baked parts. This study proves the possibility to control the structure and physico-mechanical properties of additive manufacturing parts made of powders that are obtained from waste cobalt-chromium alloys by electroerosion dispersion. This helps reduce the reliance on imported powders suitable for additive manufacturing while also cutting the cost of the final products.

Solution combustion synthesis of MnFeCoNiCu and (MnFeCoNiCu)3O4 high entropy materials and sintering thereof

Single-phase, fine-grained high entropy MnFeCoNiCu alloy and (MnFeCoNiCu)3O4 oxide powders have been pioneered by an in-situ solution combustion synthesis without post-treatment, utilizing alanine and glycine as organic reducers and ammonium nitrate as an auxiliary oxidizing agent. In order to regulate the porosity, homogeneity, phase composition and morphology of the obtained powders, multivariate studies on the influence of the following parameters were performed: type and quantity of reducers, pH of solution, ignition temperature, presence of oxidizing agent, etc.. It has been shown that the amount of the reducer holds the key for governing combustion temperature and speculation of lower and upper combustion limits in the systems under study. In turn, according to the temperature-time profiles of combustion, product microstructure, as well as phase composition of the product, the combustion area turned out to be divided into two sub-domains: volume combustion (with vigorous flaming) and self-propagation combustion. After thorough characterization, high entropy MnFeCoNiCu alloy and high entropy (MnFeCoNiCu)3O4 oxide powders were subjected to consolidation by spark plasma sintering and mechanical properties were evaluated. The influence of sintering temperature on the phase transformation of the products was revealed.