Core-shell Powders Research Articles

Synthesis and spark plasma sintering of Ti5Si3-Mo powders with core-shell structure

Core-shell Ті5Si3-Mo powders were successfully synthesized by reducing of ammonium molybdate (para) tetrahydrate with hydrogen and glycerol, respectively. As a result, the Ti5Si3 core was coated with submicron and nanosized Mo particles. The morphology and microstructure of the synthesized powders were studied scanning electron microscopy along with local chemical analysis. Phase analysis was performed using X-ray diffraction. The synthesized powders were densified by spark plasma sintering (SPS) at a temperature of 1500 °C. It was shown that powders with a core-shell structure are densified up to a temperature of 1330 °C, while the mechanical mixture of commercial powders at this temperature only begins to densify. The hardness (HV20) of the obtained composites was also investigated. Compressive strength investigation at room temperature shows 5.5 % plastic strain and ultimate strength of about 3 GPa as well as fractographic studies have shown the presence of a pseudo-brittle fracture mechanism for the metal matrix composite (MMC), which was sintered by SPS of the core-shell Ti5Si3-Mo powder synthesized by reduction with glycerol.

Effect of decomposed TiCp on the mechanical properties of laser powder directed energy depositioned Inconel 718

As the demand for high-strength materials at elevated temperatures grows, this study pioneers a novel approach to the high-temperature mechanical properties enhancement of Inconel 718 alloy, achieving this through the controlled reinforcement with titanium carbide particles (TiCp) via laser powder directed energy deposition (LPDED). Core-shell composite powders with varying TiCp content (1, 3, and 5 wt%) were prepared using the surface modification and reinforcement transplantation method. The LPDED-printed TiCp-added specimens, which were crack-free and homogeneous, exhibited a higher density compared to their pristine counterparts. Microstructural variations were observed in the as-built and heat-treated samples, which impacted the mechanical properties at room and high temperatures. Notably, the sample with a 3 wt% TiCp addition exhibited an exceptional yield strength at 800°C, demonstrating a 40 % enhancement compared to its wrought Inconel 718 counterpart while also satisfying elongation requirements at room temperature. Through the analysis of the strengthening mechanism and investigation of mechanically tested samples at high temperatures, the strengthening enhancement is mainly induced by interstitial atom clusters near the dislocations and precipitates. This investigation underscores the modification of the microstructural and mechanical characteristics through TiCp control in LPDED, offering insights into the development of high-performance metal matrix composites for high-temperature applications.

Achieving high strength and ductility of titanium matrix composite reinforced with networked TiB via SPS sintering of core-shell powder and accumulative hot rolling

Achieving high strength and ductility of titanium matrix composite reinforced with networked TiB via SPS sintering of core-shell powder and accumulative hot rolling

Synthesis of ZrB2-SiC-ZrC composite powders with core-shell structure via sol-gel molecular modulation

In this study, ZrB2-SiC-ZrC (ZSZ) composite powders with molar ratios C/(B + Zr + Si) = 1.5, 1.9 and 2.4 were obtained by sol-gel method and boro/carbothermal reduction reaction. Meanwhile, the impact of heat treatment temperature (1100 °C–1600 °C) and holding time (1 h–2.5 h) on the resulting powders were studied. The results showed that the ZSZ powder precursors were first completely converted to ZrO2, SiO2, B2O3 and pyrolytic carbon after heat treatment at 1200 °C under the optimized molar ratio (2.4) and holding time (2.5 h). Then, the transformed oxidation products and pyrolytic carbon were completely transformed into ZSZ composite powders after optimized heat treatment at 1500 °C. The synthesized ZSZ composite powders are characterized by the core-shell structure, in which ZSZ particles act as the inner core are encapsulated by the low-crystalline ZrB2 phase as the outer shell to form a core shell structure. The ZSZ composite ceramic materials prepared using the core-shell structural powders have excellent ablative properties in the range of 2000 °C, with the mass and line ablation rate of −3.5 × 10−4 g/cm3 and 2.39 × 10−3 mm/s, respectively.

Structure and plastic deformation of metastable Ag–Cu metal-matrix composites produced by a bottom-up way from Cu@Ag core–shell powders

To understand mechanical behavior of metastable metal-matrix composites, Cu@Ag core–shell powders of two compositions, 51:49 and 80:20 (Cu:Ag in wt%), were compacted by spark plasma sintering. The microstructures of these metastable metal-matrix composites are characterized by single spherical particulates of pure Cu in the matrix of pure Ag in the former case while by aggregates of Cu particulates in Ag matrix in the latter one. The plastic deformation showed enhancement of the ultimate tensile strength compared to both pure component metals by a factor of ca. 3. It is shown that a part of plastic deformation can be correlated by a logarithmic dependence but a possibility to apply a polynomial (quadratic) correlation is suggested. As expected, the shape of the particulate changes during plastic deformation and depends on the level and type of the plastic deformation. A model is proposed showing that this dependence is of a hyperbolic character.

Production of sustainable polyester composite building material using industrial waste plastic core, hemp fabric, and shrimp shell powder: Effect of quasi-isotropic fiber stacking and particle loading

Production of sustainable polyester composite building material using industrial waste plastic core, hemp fabric, and shrimp shell powder: Effect of quasi-isotropic fiber stacking and particle loading

W–CeO2 Core–Shell Powders and Macroscopic Migration of the Shell via Viscous Flow during the Initial Sintering Stage

To retard the mutual contact of W grains to inhibit their growth, in this study, CeO2·2H2O was first coated on the surface of pure W (undoped) particles by a weight percentage of 4% using a wet chemical method to prepare CeO2·2H2O-doped W-based (doped) powders, with W particles as the core and CeO2·2H2O as the shell (W–CeO2·2H2O core–shell structure), without hydrogen reduction treatment. The undoped and doped powders were subsequently sintered using a spark plasma sintering (SPS) apparatus to fabricate bulk materials. The macroscopic migration of the CeO2 shell in the core–shell W–CeO2 system via viscous flow during the initial sintering stage was studied through simulations and experiments. The results showed that a core–shell structure with W particles as the core and CeO2·2H2O as the shell was successfully prepared. The doped powder contained approximately 3.97% CeO2, consistent with the designed content of 4%. The shell materials migrated among the selected four sintered powders, filling the pores and contributing to the improvement in the relative density of the sintered bulk.

A MgZn alloy with network structure prepared by powder metallurgy with Core-Shell powder

In order to slow down the degradation rate of the magnesium alloys, a core–shell powder with a layer of Zn coated on the surface of Mg particles was prepared by eletroless plating, and then was compacted and sintered to form a Mg-Zn alloy with a network structure (net MgZn alloy), in which a network structure of Zn alloy wraps around Mg grains. The strength of the net MgZn alloy is 102 MPa, which is slightly lower than that of the pure Mg. The degradation rate of the net MgZn alloy is about 25 % of pure Mg after 4 days immersion in simulated body fluid (SBF), at which time pure Mg was completely dissolved. Hydrogen evolution for the net MgZn alloy increased gradually and linearly and had not a rapid increase.

Study on hydrogen reduction mechanism of MoO3 using Ti–Mo core–shell powder

In this study, the hydrogen reduction mechanism of MoO3 was analyzed in detail using Ti–Mo core–shell powder manufactured through a milling and reduction process. MoO3 and Ti powders were ball-milled to refine the MoO3 powder and coat it onto the Ti powder to fabricated core-shell structure. Subsequently, the milled powder was heat-treated at 600°C in a hydrogen atmosphere to reduce MoO3 to nano-sized Mo. In addition, the reduction behavior of MoO3 was analyzed by varing the reduction times to 1, 10, 30 min and 1, 3, 5 h. Phase analysis was conducted using X-ray diffraction, and oxidation state analysis was conducted using X-ray photoelectron spectroscopy. Morphology analysis was performed using scanning electron microscopy, and elemental analysis was conducted using electron probe micro-analysis. It was confirmed that Mo9O26 and Mo4O11 intermediate phases were formed sequentially as MoO3 was reduced to MoO2, and Mo9O26 had a plate shape with a thickness of sub-70 nm, and Mo4O11 exhibited a thickness of sub-300 nm. Especially, the Mo2O3 intermediate phase, previously studied only theoretically, was experimentally confirmed for the first time in the reduction process from MoO2 to Mo. Furthermore, the analysis of Mo-oxide intermediate phases was explained by the structural characteristics of the core–shell. The shell of Mo oxide was thick and dense, making it difficult for the vapor phase necessary for CVT reduction to penetrate and diffuse into the shell. As a result, the rapid CVT reduction occurred outside the shell, while relatively slower reduction occurred inside the shell where intermediate phases were observed.

The distribution of reinforcements in titanium matrix composites enhanced with graphene: From dispersed to networked

Designing the reinforcement distribution and thus tailoring the matrix microstructure can be leveraged to achieve titanium matrix composites (TMCs) with well-balanced strength and ductility. In this study, through the utilization of mechanical exfoliation to synthesize core-shell structure powders in-situ and spark plasma sintering subsequently, graphene nanoplatelets (GNPs) reinforced Ti6Al4V composites (GNPs/Ti64) with manageable ductility were successfully fabricated. The increasing incorporation of GNPs leads to the reinforcements' transition from dispersed to networked together with the microstructural equiaxialization, which is reflected in a monotonically increasing strength in conjunction with a bimodal distribution of ductility. As a result, both 0.13 wt% GNPs/Ti64 with dispersed reinforcements and 0.70 wt% GNPs/Ti64 with quasi-continuous networked reinforcements possess the well-balanced strength-ductility. This study suggests a practical strategy by regulating the reinforcement distribution for TMCs with attractive properties.

Ultrahigh-strengthened intragranular κ-Al2O3 nanoparticles dispersed Mo composite prepared via SPS sintering of core-shell Mo nanocomposite powder

Oxide dispersion strengthening (ODS) is an effective method to improve the mechanical properties of Mo-based materials. However, the mechanical properties of traditional ODS-Mo composites are always limited by the coarsening and intergranular distribution of second-phase particles. In this work, an effective nano-reinforcement dispersion strategy was developed to fabricate an ODS-Mo composite with ultrafine grain and intragranular distribution of second-phase particles. Core-shell structural Mo nanocomposite powders, with internally distributed sub-10 nm Al2O3 dispersoids, were prepared by nano atomization doping (AD) followed by a chemical vapor transport growth strategy. Then, ODS-Mo composites with ultra-fine Mo grain (below 700 nm) and high-density intragranular κ-Al2O3 (below 20 nm) nanoparticles were prepared via spark plasma sintering (SPS), in which a coherent interface between κ-Al2O3 and Mo matrix was formed. The composites present remarkably improved hardness (above 500 HV), bend strength, and compressive yield strength (above 1664 MPa) at room temperature, with a suitable strain to fracture of 27.1 %. The calculation of strengthening mechanisms indicates that the enhancement was mainly attributed to the intragranular κ-Al2O3 nanoparticles. This nano-sized reinforcement distributed within the grain can more effectively pin dislocations and achieve dispersion strengthening in ODS-Mo composites. Therefore, this strategy can efficiently construct intragranular second-phase nanoparticles and open up new avenues to fabricate high-performance ODS-Mo composites.

Preparation and interface analysis of Gd2O3@W core-shell powders as co-shielding absorbers for neutron and gamma-ray

Gd2O3 is often used as an absorber in nuclear fuel shielding because of its excellent neutron absorption capacity. However, Gd element releases prompt gamma rays when absorbing neutrons, which threatens the safety of personnel and equipment. In this paper, a new absorber, Gd2O3@W core-shell powder, is proposed, which can simultaneously absorb thermal neutrons and prompt gamma rays. Firstly, MCNP5 software was used to explore the influence of tungsten layer thickness on γ-ray attenuation ratio, and the thickness of tungsten layer required to shield prompt γ-ray was obtained. Then, in order to explore an effective tungsten plating method, Gd2O3@W core-shell powders were prepared by three methods: powder coverage sintering, sol-gel method and immersion method. The Gd2O3@W core-shell powders prepared by the above three methods were observed and analyzed by SEM and EDS. The results show that the core-shell powder prepared by immersion method is more uniform and dense. Finally, the composition and shell thickness of the Gd2O3@W core-shell powder prepared by immersion method was further studied. The results show that the W layer thickness is about 200–600 nm, and there is a diffusion zone between the shell and the core, resulting in new phases Gd2W2O9 and Gd2WO6. The prepared Gd2O3@W core-shell powder in this paper.can be used as a co-absorber of neutron and gamma rays for shielding composites.

Fabrication of Ti-Mo Core-shell Powder and Sintering Properties for Application as a Sputtering Target

Fabrication of Ti-Mo Core-shell Powder and Sintering Properties for Application as a Sputtering Target

Influence of Ni Content on Microstructure and Hardness of Nickel-Graphite Abradable Seal Coatings Produced by Plasma Spraying

The influence of the initial shape of graphite powder and Ni content on the structure and properties of the nickel-graphite powders and plasma-sprayed coatings is investigated. The irregularly and spherically shaped graphite powders were produced by mechanical crushing and mechanical crushing with rolling, respectively. It is shown, that spherically shaped graphite powder has advantages in flowability and better deposition of Ni layer. The nickel-graphite core-shell powders with 50 and 75 wt.% Ni content were used to deposit coatings by plasma spraying. The composition, structure, and hardness of the nickel-graphite coatings were studied.

Heterointerface regulation of core-shell FeSiAl magnetic powders by in situ oxidation as high-efficiency absorbers

Developing electromagnetic (EM) absorbers that are highly efficient across a wide bandwidth is a significant hurdle in mitigating the growing issue of EM pollution emanating from the increasing prevalence of electronic and telecommunication devices. When considering the applications of absorbers in high-temperature environment, ensuring both structural and chemical stability becomes crucial. Incorporating a magnetic core and dielectric shell within core-shell structures appears to be a promising strategy for addressing this challenge. In this work, we have successfully synthesized the core-shell FeSiAl@oxide composites through in situ oxidation process, which offers a facile route for significantly enhancing their EM absorbing performance by promoting multiple interfacial polarizations and achieving ideal impedance matching. A systematic analysis has been conducted to uncover the morphological and microstructural evolution of the FeSiAl@oxide composites, shedding light on their EM properties. The remarkable EM dissipation capacity of these composites, owing to the strong synergistic effects between magnetic and dielectric losses, has been demonstrated with the minimum absorption of −41.7 dB over an impressive absorption bandwidth of 7.92 GHz at 2.5 mm.

Preparation of Fe@Fe3O4/ZnFe2O4 Powders and Their Consolidation via Hybrid Cold-Sintering/Spark Plasma-Sintering.

Our study is focused on optimizing the synthesis conditions for the in situ oxidation of Fe particles to produce Fe@Fe3O4 core-shell powder and preparation via co-precipitation of ZnFe2O4 nanoparticles to produce Fe@Fe3O4/ZnFe2O4 soft magnetic composites (SMC) through a hybrid cold-sintering/spark plasma-sintering technique. XRD and FTIR measurements confirmed the formation of a nanocrystalline oxide layer on the surface of Fe powder and the nanosized nature of ZnFe2O4 nanoparticles. SEM-EDX investigations revealed that the oxidic phase of our composite was distributed on the surface of the Fe particles, forming a quasi-continuous matrix. The DC magnetic characteristics of the composite compact revealed a saturation induction of 0.8 T, coercivity of 590 A/m, and maximum relative permeability of 156. AC magnetic characterization indicated that for frequencies higher than 1 kHz and induction of 0.1 T, interparticle eddy current losses dominated due to ineffective electrical insulation between neighboring particles in the composite compact. Nevertheless, the magnetic characteristics obtained in both DC and AC magnetization regimes were comparable to those reported for cold-sintered Fe-based SMCs.

Tetradecahedral Cu@Ag core–shell powder with high solid-state dewetting and oxidation resistance for low-temperature conductive paste

We demonstrate a novel tetradecahedral Cu@Ag core–shell powder with large Ag shell grains, which has better solid-state dewetting resistance, oxidation resistance and conductivity compared to conventional spherical Cu@Ag core–shell powder.

Sintering property of micro/nano core-shell molybdenum powder synthesized by mechanochemical process

In this study, a micro/nano core-shell molybdenum powder was synthesized by mechanochemical process to improve its microstructural uniformity and density by pressureless sintering the core-shell powder. The micro-sized spherical Mo powder, prepared through an electrode induction melting inert gas atomization process, was mixed with MoO3 powder and ball-milled using a three-dimensional shaker mixer. A mechanochemical process involving hydrogen reduction was employed to prepare the core-shell Mo powder. The prepared powders were sintered through the compacting and pressureless sintering. The density was measured using a densitometer to analyze the properties of sintered specimens. Phase analysis was performed using X-ray diffraction. In addition, microstructure analysis was conducted using scanning electron microscopy and electron backscatter diffraction. Comparing the sintered core-shell powder to the sintered conventional mixing powder under the same conditions, we observed that the former exhibited a uniform microstructure and higher density. Furthermore, we experimentally demonstrated the dependence of sintering properties on mixing ratio.

Mesoscopic Simulation of Core-Shell Composite Powder Materials by Selective Laser Melting.

Mechanical ball milling is used to produce multi-materials for selective laser melting (SLM). However, since different powders have different particle size distributions and densities there is particle segregation in the powder bed, which affects the mechanical properties of the printed part. Core-shell composite powder materials are created and used in the SLM process to solve this issue. Core-shell composite powder materials selective laser melting (CS-SLM) has advanced recently, expanding the range of additive manufacturing applications. Heat storage effects and heat transfer hysteresis in the SLM process are made by the different thermophysical characteristics of the core and the shell material. Meanwhile, the presence of melt flow and migration of unmelted particles in the interaction between unmelted particles and melt complicates the CS-SLM molding process. It is still challenging to investigate the physical mechanisms of CS-SLM through direct experimental observation of the process. In this study, a mesoscopic melt-pool dynamics model for simulating the single-track CS-SLM process is developed. The melting characteristics of nickel-coated tungsten carbide composite powder (WC@Ni) were investigated. It is shown that the powder with a smaller particle size is more likely to form a melt pool, which increases the temperature in the area around it. The impact of process parameters on the size of the melt pool and the distribution of the reinforced particles in the melt pool was investigated. The size of the melt pool is significantly affected more by changes in laser power than by changes in scanning speed. The appropriate control of the laser power or scanning speed can prevent enhanced particle aggregation. This model is capable of simulating CS-SLM with any number of layers and enables a better understanding of the CS-SLM process.

Thermodynamics aided design of hBN-capsulated diboride powders from novel nitrate precursors for high entropy ceramics

Hexagonal BN-coated powders have been widely used in various engineering sectors, however, their productions are restricted by the complexity of gas-solid reactions. In this study, guided by thermodynamics, a novel approach to synthesize Layer-structured hexagonal BN (hBN)-coated high entropy diboride powders in vacuum was developed, using metal salt Zr(NO3)4·5H2O, HfCl4, NbCl5, TaCl5, C16H36O4Ti, boric acid, and sucrose as raw materials. By adjusting the ratio of carbon to metal source (C/M), powders only consisting of two boride solid solutions and hBN were finally obtained, under an optimal processing condition of C/M = 5.5 and synthesis temperature of 1400 °C. Parts of hBN were found to coat on high-entropy metal diborides ceramic (HEB) particles, corresponding formation mechanism for core-shell structured powders was investigated, together with the liquid precursor assisted boro/carbothermal reduction process. Starting from as-synthesized core-shell powders, (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2–11 vol% hBN ceramics were densified at 1900 °C under 50 MPa without holding, with a high relative density of 97.3%.