Spherical Powders Research Articles

Three-Dimensional Numerical Simulation of High-Speed Shear Crushing of High-Density Fluid

Plasma atomization is a technology that can produce high sphericity, small particle diameters, and high-purity copper powder, which is of great significance for the development of metal additive manufacturing. At present, although plasma atomization can realize the industrial preparation of spherical copper powder, there are still some problems, such as unclear understanding of the atomization process and a lack of theoretical support for powder quality control. This leads to the inability to predict the average particle diameter of powder in advance based on the actual atomization conditions and to optimize the process parameters, which seriously affects the further development of the plasma atomization process. We mainly studied the non-stationary simulation of a DC argon plasma torch. The purpose of this paper was to study the specific influence law of the average particle diameter of the powder in the process of plasma atomization by means of numerical simulation and experimental observation. The aim was to establish the mapping relationship between the atomization condition and the average particle diameter of the powder and realize the controllable preparation of the plasma atomized powder. At the same time, we used industrial-grade plasma atomization equipment to carry out pulverizing experiments to verify the plasma atomization theory and the powder average particle diameter control scheme proposed in this paper, thus proving the reliability of this study.

Improvements in mechanical property and corrosion resistance of Ti-6.5Al-2Zr-1Mo-1V fabricated by laser powder bed fusion using cost-effective modified hydride-dehydrided powder

Due to higher mechanical properties and shorter fabrication time, Ti-6.5Al-2Zr-1Mo-1V (TA15) fabricated by laser powder bed fusion (LPBF) is gaining increasing attention. However, the high cost of raw powder limits its wide application. In this study, TA15 is fabricated by LPBF using cost-effective modified HDH powder (LPBF-ed modified HDH). Microstructure, mechanical properties, and corrosion resistance of the fabricated sample are investigated and compared systematically with sample fabricated by LPBF using gas atomization (GA) spherical powder (LPBF-ed GA). The result shows that both two samples can achieve full density at the optimized process parameters and consist of α′ phase. But compared with LPBF-ed GA sample, the volumetric energy density (VED) of LPBF-ed modified HDH decreases about 60 % (41.15 vs. 94.65 J/mm3), which makes the LPBF-ed modified HDH sample exhibit finger grain size (decreasing from 0.231 μm to 0.129 μm). Such differences together with different interstitial element content result in LPBF-ed modified HDH samples exhibiting higher mechanical properties and corrosion resistance compared with LPBF-ed GA sample, namely tensile strength and elongation improves about 10 % (from 1286.1 MPa to 1353.7 MPa) and 100 % (from 5.8 % to 11.2 %), respectively, while corrosion current density (Icorr) and passivation current density (Ip) reduces about a half (from 2.98 × 10−8 A/cm2 and 4.07 × 10−6 A/cm2 to 1.03 × 10−8 A/cm2 and 2.54 × 10−6 A/cm2, respectively). Furthermore, the cost analysis result indicates that the cost of modified HDH powder was reduced by 60 % compared with GA powder (50 vs. 120 $/kg). Cost-effective raw materials together with a good combination of tensile strength and elongation and excellent corrosion resistance make LPBF-ed modified HDH parts exhibit broad application prospects, especially in the fields of aviation and maritime.

Preparation of spherical Gd2Zr2O7 powders by RF induction thermal plasma process

Spherical Gd2Zr2O7 (GZO) powders with a uniform particle size distribution are successfully prepared using a novel industrial approach, which combines spray-drying process and thermal plasma sintering technology together. In this, GZO powders with pyrochlore structure as the main phase are first synthesized via a solid-state reactive route using a mixture of the milled Gd2O3 powders and ZrO2 powders as starting materials. The influence of sintering temperature on the microstructure of prepared powders is researched. Then, GZO granules are prepared after wet-grinding and spray-drying process, which exhibit a spherical shape with the average particle size of 46.5 μm. RF induction thermal plasma is finally used to sinter the granulated particles, and the influence of feeding rate on the properties of spherical powders is investigated. The apparent density of plasma sintered GZO spherical powders is increased from 1.53 g/cm3 to 2.29 g/cm3 when the feeding rate of granulated powders is 80 g/min, and further increased up to 3.90 g/cm3 when the feeding rate is 15 g/min. Such powders are in potential demand for plasma sprayed coatings and additive manufacturing techniques, and the successful synthesis of spherical GZO powders may guide the way toward the preparation of many other spherical rare earth zirconates powders.

Spherical Submicron Powders with a Nanopolycrystalline Superstructure—a Promising Raw Material for Obtaining Fine-Grained High-Density Ceramics

Spherical Submicron Powders with a Nanopolycrystalline Superstructure—a Promising Raw Material for Obtaining Fine-Grained High-Density Ceramics

Development of hybrid technology of producing spherical powders from wire materials using high-speed plasma jets and electric arc

Development of hybrid technology of producing spherical powders from wire materials using high-speed plasma jets and electric arc

Development of hybrid technology of producing spherical powders from wire materials using high-speed plasma jets and electric arc

Development of hybrid technology of producing spherical powders from wire materials using high-speed plasma jets and electric arc

Synthesis of uniform spherical silver powder without dispersants in a confined impinging-jet reactor

Sliver powder is the most common and extensively utilized precious metal powder in electronics, primarily for electronic paste. Herein, micron-sized spherical silver powder was synthesized via a liquid phase reduction method employing silver nitrate as the source of silver and ascorbic acid as the reducing agent in a confined impinging jet reactor (CIJR). The impact of the molar ratio between silver nitrate and ascorbic acid, the flow rate, and the temperature on the particle size of silver powder was investigated. The optimal process conditions for silver powder are as follows: maintain a molar ratio of 1:1 and control the feeding rate at 10 ml/min while operating at 50 ° C. The confined impinging jet reactor offers enhanced control over reaction conditions during the synthesis of silver powder, surpassing the capabilities of traditional batch reactors. The aforementioned optimized methodology was employed to successfully synthesize uniform and spherical silver powder (with an aspect ratio approaching 1) in the low Reynolds number jet, resulting in an average particle size of d50 = 0.83 μm and a standard deviation of 0.07, without the addition of dispersant. The synthesis method presented here improves the performance of silver powder, simplifies the production process, reduces energy consumption, and minimizes waste generation. These advances yield significant environmental and economic benefits. In the future, with the continuous development and optimization of microreactor technology, this synthesis method is anticipated to play a more prominent role in the commercial-scale production and application of micrometer-sized silver powder.

Особенности применения электродов-инструментов, изготовленных аддитивными технологиями, при электроэрозионной обработке изделий

Introduction. The paper presents the results of a study of the use of a tool electrode (TE), manufactured by selective laser alloying from MS1 maraging steel powder for copy-piercing electrical discharge machining (EDM). Purpose of the work: experimental study of the features of the use of additively manufactured TE in the EDM of critical products. Research methods. The specimens were prepared using a ReaLizer SLM 50 system. The starting material was spherical MS1 powder with an average particle size of 30 μm. To test the modes and select a TE sample with the least number of surface defects, four manufacturing modes were tested, and the best TE sample was selected for further research. The EDM was carried out on EMT Smart CNC equipment in a dielectric oil environment. The specimens were installed in a clamp with straight polarity and were used as TE; a 0.12C-18Сr-10Ni-Тi steel plate served as the workpiece electrode. The study was conducted using a factorial experiment (type 23) with a central design. The input data of the factorial experiment is the current I (A), voltage U (W), pulse on time Ton (μs). The output parameters were the roughness parameter Ra and tool electrode wear γ. The roughness parameter Ra was measured using a Mahr Perthometer S2. Results and discussion. TE samples were made from MS1 powder using the SLS method; the highest quality TE sample No. 4 was selected for EDM. Empirical equations are obtained that describe the relationship between the roughness parameter Ra and tool electrode wear γ, depending on the EDM modes. At the minimum mode with a current I = 4 A and a voltage U = 50 V, the tool electrode wear is γ = 0.0063875 g. The maximum tool electrode wear is γ = 0.13938 g with a current I = 8 A and a voltage U = 50 V. It is established that at a constant pulse on time Ton = 75 μs, the smallest roughness Ra = 2.83 μm is obtained at a current of I = 4 A and a voltage U = 100 V, and the maximum roughness is Ra = 4.1568 μm at I = 8 A and U = 100 V.

Chemical strengthening of glass powder particles

It is well known that chemical strengthening of glass brings the benefit of increased fracture strength. Despite extensive research on processing and mechanics at the macroscale, the effectiveness of chemical strengthening on glass elements with all three dimensions in the micrometer regime remains largely unexplored. Here, we develop a novel process for chemical strengthening of micrometer-sized spherical glass powder particles and study the fracture behavior of these particles with in-situ particle compression tests inside a scanning electron microscope. Cross-sectional microscopy and energy dispersive spectroscopy measurements confirm ion exchange and show an increase in diffusion depth with an increase in processing time and temperature. We report a higher fracture strength for chemically strengthened powder particles compared with the as-received ones. We show that the increase in fracture strength is associated to the compressive residual stress resulting from ion exchange during chemical strengthening.

Towards high-density and thick-walled NiFe2O4-based cermet by ceramic injection molding using spherical composite powder

Ceramic injection molding (CIM) is a near-net-shape technology for the rapid manufacture of complex-shaped small parts. Preparation of thick-walled parts remains a challenge owing to the difficulty in debinding process for green body based on micron and irregular ceramic powders. In this study, spherical metal-ceramic composite powders with different particle sizes were prepared using a wet granulation method. NiFe2O4-based cermets with a thickness of 20 mm were fabricated using both spherical (SP) and non-spherical (NSP) powders as raw materials. Roles of the powder shapes in catalytic debinding and sintering behaviour were investigated. Compared with that of NSP, green body with SP exhibited improved debinding efficiency, due to the well developed pore channels. A new perspective was proposed to explain the mass transfer mechanism during the debinding process. The adoption of spherical composite powders significantly enhanced the debinding rate without affecting the sintering performance. After sintering, sound cermet parts with uniform microstructure and the highest relative density of 98.62 % were achieved. This provides an important reference for the fabrication of large and thick-walled parts by CIM via controlling the powders.

Microstructure and tensile properties of transient liquid phase (TLP) sintering repaired Ti–6Al–4V alloys with large area hole defect

Repairing defects in titanium alloy components is economically justified due to their high cost. In this work, Ti–6Al–4V samples with large area hole defects are repaired by transient liquid-phase sintering. The microstructure and tensile properties after repair have been investigated. The factors of different base powder morphology and the ratio of braze metal are also studied. The results show that by using spherical Ti64 alloy powder with 40 wt% TiZrCuNi braze alloy powder, an overall repair effect with high-density repair zone and good interface combination can be obtained at 960 °C for 3 h. The tensile strength of the as-repaired exceeds that of the matrix, but the elongation is lower than that of the matrix. Finally, the repair experiment conducted at various angles demonstrates this technique's strong practical feasibility.

Preparation of spherical NiO-8YSZ composite powder through spray drying

Homogeneous sphere NiO-8YSZ composite powder with a narrow size distribution is significant for the fabrication of high-quality solid oxide fuel cell (SOFC) anodes. In this study, spray drying was used to prepare evenly distributed and spherical NiO-8YSZ composite particles used for the fabrication of SOFC anodes. The result showed that the particles prepared with a solid content of 65 wt %, atomizing pressure of 60 kPa, drying temperature of 180 °C, and sintering at 1200 °C for 2 h exhibited the best holistic quality with high sphericity (90 % over 0.84), narrow size distribution (D10 = 27.78 μm, D90 = 45.49 μm), high collection rate (70 %), and low content of unstable phases. The influence of these main parameters on the quality of the prepared particles was investigated and discussed as well. It was found that the solid content and the atomizing pressure demonstrated opposite effects on the particle size, with the former showing a positive correlation and the latter showing a negative correlation. The drying temperature decided the agglomeration degree of the prepared powder, which was involved in the presence of grape-like particles. In addition, the collection rate appeared to be positively correlated with the solid content and the atomizing pressure. The atmospheric plasma sprayed coating fabricated using the sprayed-dried powder prepared with the optimal parameters demonstrated significantly improved micromorphology and structure when compared with the coating fabricated using the mechanical mixed composite powder, which proved the prominent advantage of the powder produced through this spray drying method. All these progresses were considered good instructions for the studies on powder granulation and its applications in manufacturing high-quality coating materials.

Impact of Chemical Composition Changes during Ultrasound Atomization and Laser Powder Bed Fusion of Low Alloy Steel

This study investigates the effect of changing the chemical composition during ultrasonic atomization (UA) and laser powder bed fusion (LPBF) of low‐alloy steel. UA is used to produce a spherical powder with d50 equal to 49 μm. During UA, the chemical composition of the material changes, which is associated with selective evaporation of Mn from 1.42% to 0.35% and B from 0.0012% to <0.0001%. Thermodynamic calculations confirm that during atomization, mostly Mn and Fe evaporate. To achieve a high density of 3D printed parts, in situ remelting in LPBF is applied. A microstructure consisting of fine grains of tempered martensite and bainite in crystallized meltpools is observed. The selected high‐quality LPBF samples are austenitized in the temperature range of 900–1200 °C for 20 min and quenched in oil. The samples are characterized by light and scanning electron microscopy, as well as Vickers hardness. Changes in chemical composition result in a decrease in the hardenability of the material, and quenching only at 1200 °C produces a martensitic microstructure. LPBF samples show a hardness higher than that of the postheat‐treated sample, but still significantly lower than that of the as‐delivery condition, which is related to the change in chemical composition.

Effect of Laser Power on Microstructure and Properties of WC-12Co Composite Coatings Deposited by Laser-Based Directed Energy Deposition.

During the laser-based directed energy deposition (DED-LB) processing, a WC-12Co composite coating with high hardness and strong wear resistance was successfully prepared on a 316L stainless steel substrate by adopting a high-precision coaxial powder feeding system using a spherical WC-12Co composite powder, which showed a large number of dendritic carbides and herringbone planar crystals on the substrate-binding interface. The influences of laser power on microstructural and mechanical properties (e.g., hardness, friction resistance) of WC-12Co composite surfaces were investigated. The results show that laser power has a significant effect on determining the degree of Co phase melting around the WC particles and the adhesion strength between the matrix and the coating. Lower laser power does not meet the melting requirements of WC particles, thus weakening the molding quality of the composite coating. At high laser power, it is possible to dissolve the WC particles and melt the metal powder between the particles, thus improving the material properties. The laser power increased from 700 W to 1000 W and the average hardness of the coating surface gradually increased from 1166.33 HV to 1395.70 HV, which is about 4-5 times higher than the average hardness of the substrate (about 281.76 HV). In addition, the coatings deposited at 1000 W showed better wear resistance. This work shows that the processing parameters during laser-directed energy deposition can be optimized to prepare WC-12Co composite coatings with excellent mechanical properties.

Application of 3D-printed individualized porous tantalum buttress in shelf acetabuloplasty for developmental dysplasia of the hip

Shelf acetabuloplasty is a viable treatment for developmental dysplasia of the hip (DDH), yet autologous bone grafts have faced challenges such as morphological mismatch, imprecise placement, and long-term graft resorption. The rapid advancement of three-dimensional (3D) printing technology in orthopedics has enabled the acquisition of digital image correlation method (DICM) data from patient pelvic to bilateral femoral proximal regions through computed tomography (CT) scans. This data is then utilized by software to create 3D models and design individualized metal implants. Using tantalum-based TA1 type I spherical powder as the raw material, a porous tantalum buttress with a pore size of 600 microns and a porosity of 75% was fabricated employing the selective electron beam melting (SEBM) technology. Our Center has applied this 3D-printed individualized porous tantalum buttress in shelf acetabuloplasty for 21 DDH patients (25 hips), including 6 males and 15 females, with a mean age of (21.38±7.39) years. The follow-up period ranged from 12 to 47 months, averaging (22.64±10.86) months. At the final follow-up, patient-reported outcomes (PROs) were used to assess patient’s subjective feelings. Significant improvements were observed in the Non-Arthritic Hip Score (NAHS), modified Harris Hip Score (mHHS), Hip Outcome Score-Sports Subscale (HOS-SSS), International Hip Outcome Tool-12 (iHOT-12), and Visual Analog Scale (VAS) compared with preoperative levels (P<0.01). Radiographic assessments showed that postoperative lateral center edge (LCE) angle, Tonnis angle, acetabular angle (Sharp’s angle), and femoral head coverage all trended towards normal, with statistically significant differences (P<0.01). There was no implant displacement or bone resorption in any case, and no progression in Tonnis grading for hip osteoarthritis (OA) was noted postoperatively, with an 84% patient satisfaction rate. The early follow-up results of 3D-printed individualized porous tantalum buttress in shelf acetabuloplasty are satisfactory, indicating a reliable application prospect for the treatment of DDH patients.

Fine grains, dispersed phases and strong crystal defect interactions inducing excellent strength-ductility synergy in powder sintered Cu–18Sn-0.3Ti alloy via hot extrusion and solution treatment

In order to prepare the Cu–18Sn-0.3Ti alloy with excellent mechanical properties to realize the favorable collaborative deformation of Cu–18Sn-0.3Ti alloy and Nb in the preparation process of Nb3Sn superconducting wires by bronze method, the hot extrusion process of the Cu–18Sn-0.3Ti alloy prepared by Direct Current assisted Hot Pressed sintering based on micron atomized spherical alloy powders was systematically investigated by the combination of experiments and finite element simulation in this work. The ultimate tensile strength, yield strength and elongation can reach 683.5 MPa, 414.3 MPa and 33.3 %, respectively, through the optimization of hot extrusion parameters and subsequent solution treatment. The results show that hot extrusion with high strain rate induced the formation of fine α grains and dispersed δ phases. Especially, strong dislocations-annealing twins (ATs) interaction occurred, which was manifested as the pile-up of dislocations at twin boundaries of ATs, slippage of dislocations in multiple directions inside ATs and storage of dislocations inside ATs. Meanwhile, the high strain rate induced the formation of deformation twins inside partial grains. The grain refinement of α matrix, formation of dispersed δ phases and strong interactions of crystal defects were the main reasons for the strength-ductility enhancement of hot extruded samples, and laid an excellent microstructure foundation for further improving the mechanical properties of alloy by subsequent solution treatment. The results not only describe a feasible method for simultaneously enhancing the strength and ductility of Cu–18Sn-0.3Ti alloy, but also provide a theoretical guidance for the strength-ductility enhancement of multicomponent alloys.

Spherical nanocrystalline ScYSZ thermal barrier material by a novel supersonic plasma spheroidization method: Simple synthesis and excellent performance

The performance of plasma sprayed thermal barrier coatings (TBCs) is strongly dependent on the quality of the feedstock powders, which usually are fabricated by conventional spray drying and multi-step sintering methods. In this work, a novel supersonic plasma spheroidization technology was employed to fabricate the spherical nanocrystalline Sc2O3-Y2O3 co-stabilized ZrO2 (ScYSZ) powder. The deformation process from the irregular powder to the spherical one was stimulated by the COMSOL phase field simulation. The results suggested that the original irregular pyrolysis products of ScYSZ precursors were aggregated into spherical powders by plasma spheroidization technology. The COMSOL simulations verified that the powder changed from irregular particles to spherical ones. The spheroidized ScYSZ particles exclusively consisted of non-transformed t’-ZrO2 phase and showed good fluidity, smooth surface and high apparent density, which were expected to have a broader application prospect in the field of TBCs and other ceramic coatings.

Microwave spheronization of polyetherimide powder in plasticizer liquids for laser powder bed fusion

Preparing spherical powders from high-performance engineering plastics is usually challenging due to their high characteristic temperatures and excellent chemical resistance. This study reported an innovative liquid-phase microwave heating method for rapid spheronization of amorphous polyetherimide (PEI) powder and explored the processability of resultant powder in laser powder bed fusion (PBF-LB). The results indicated that the microwave process conditions, including the type of plasticizer liquids and microwave time, significantly influenced the spheronization effect and physicochemical properties of the powder. The plasticizing effect of the liquid largely reduced the glass transition temperature and melt viscosity of PEI particles, promoting their spheronization process. Spheronization enhanced the PBF-LB processability of PEI powder and reduced structural defects in parts, thereby leading to improved mechanical properties. Furthermore, its valuable flame-retardant properties were largely preserved. These findings showed the power of microwave spheronization in plasticizer liquids for advancing the application of optimized high-performance engineering plastic powders in the field of PBF-LB.

Influence of evolution in reinforcement scale characteristic parameters on the microstructure and properties of Ti6Al4V-TiBw composites fabricated by electron beam powder bed fusion

The size, aspect ratio, and distribution of reinforcement, referred to as the scale characteristic parameters (SCP), are critical factors that influence the mechanical properties of discontinuous reinforced titanium matrix composites (DRTMCs). To investigate the impact of SCP evolution on the microstructure and mechanical properties of TiBw, this study employed spherical Ti6Al4V-TiBw composite powder prepared by electrode induction melting gas atomization (EIGA) as feedstock for fabricating Ti6Al4V-TiBw composites through electron beam powder bed fusion (EB-PBF) process. By implementing a two-step rapid cooling approach in EIGA and EB-PBF processes to “freeze” the TiBw at nanoscale within Ti6Al4V-TiBw composites, a significantly wider regulation window for microstructure and mechanical properties was achieved. Subsequently, heat treatment was conducted at temperatures ranging from 850 to 1200 °C to systematically elucidate the mutual influence regulation among SCPs, microstructure, and mechanical properties of TiBw. Based on our findings, it can be concluded that when subjected to heat treatment temperatures higher than 950 °C, an orientation relationship between TiBw and α-Ti is observed: {0001} α-Ti//{001} TiBw, {11 2‾ 0} α-Ti//{010} TiBw, {10 1‾ 0} α-Ti//{100} TiBw. Additionally, the cross-section of columnar-shaped TiBw exhibits semi-coherent interfaces with coherent interfaces bonded to Ti along its (100) crystal plane while displaying incoherent interfaces with Ti matrix along its (101) and (10 1‾) crystal planes. The strength of Ti6Al4V-TiBw composites exhibited a trend of initial increase followed by decrease with the evolution of TiBw scale characteristic parameters, while the elongation demonstrated an overall decreasing pattern. This research aims to establish a foundation for microstructure and properties control of DRTMCs and provide experimental references and theoretical basis for high-performance DRTMCs research.

Microstructural investigation of nanocrystalline Nd-Fe-B magnets fabricated by laser powder bed fusion

Nd-Fe-B magnets were manufactured by laser powder bed fusion (LPBF) using commercially available spherical powder (MQP-S-11-9). The magnets were manufactured at four different volume energy densities but similar relative densities to investigate the relations between the process, structure, and characteristics. Unlike the nanocomposite microstructure of the initial powder, the microstructure of the LPBF samples had (Nd, Pr)2Fe14B grains separated by grain boundary phases through the remelting and solidification of the initial powder. The cooling rate of the melt pool increased as the volume energy density decreased, suppressing the crystallization of α-Fe in the grain boundary phase. When the volume energy density was less than 86 J/mm3, the crystallization of α-Fe was fully suppressed, and the grain boundary phases became amorphous, resulting in higher coercivity than that of the initial powder. The magnet with the strongest magnetic properties of Hci = 10.3 kOe, Br = 6.2 kG, and (BH)max = 7.5 MGOe was produced when LPBF was performed under the conditions of P90, V500, H70, and L30 (volume energy density = 85.7 J/mm3). The solidification behavior of Nd-Fe-B magnets during LPBF was analyzed in detail using thermodynamic simulations. In this study, the microstructure of the fusion zone (FZ) and the heat affected zone (HAZ) according to process parameters was analyzed, and the effect of the solidification microstructure on the magnetic properties of Nd-Fe-B magnets was reported.