Spherical Powder Particles Research Articles

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.

Модель формування пористості брикетів губчастого титану на стадії спікання

This article examines the peculiarities of the formation of interparticle connections in porous products based on titanium powders using sponge titanium as an example, which are used in the aviation industry and airfield management. The developed model is based on the results of a previous study, where the structure of cuboctahedral and inverse cuboctahedral clusters of packing spherical powder particles was determined at the most dense packing. During the study, a model of the fusion of particles at the points of pressing deformation due to recrystallization under the influence of high temperatures in a vacuum was developed. 4 main stages of powder briquette sintering were considered, and a mathematical model was developed for each of them. Thus, the stage of liquid evaporation is considered from the viewpoint of the cavitation effect of boiling on the surface of particles and boiling of plasticizers. Euler's film boiling formula was used to describe the forces acting on the particle surface; Tolubinsky's formula was used for bubble boiling; convective heat exchange was considered part of the final stage of sintering. The stage of the formation of metallic bonds is modeled on the basis of the results of practical studies in the REV 5.5 furnace, recrystallization based on differential scanning colorimetry on the NETZSCH STA 449F1 Proteus device, and determining the change in grain size according to the E19 ASTM scales using the Jeffers method. The diffusion stage is modeled on the basis of the approximation of the particle deformation model in the contact zones at the pressing stage using the Frenkel formula. Linear shrinkage is modeled based on direct measurement of sample sizes before and after sintering. The developed model has a certain versatility when applied to simulate the interaction of particles of metal powders under the conditions of the formation of porous briquettes, especially if the shape of the particles is close to round or spongy. The obtained result will make it possible to more accurately evaluate such a factor as the adhesion between the particles of the pressing and predict the tensile strength of the material. Additionally, due to the mathematical characterization of the peculiarities of the formation of corpuscular porosity under the conditions of sintering in a vacuum, we can design materials with differentiated porosity, as well as lay the foundations for powder 3D printing of such materials, by assembling grain by grain, or layer by layer with the adjustment of the force of particle compression one into the other.

Automatic characterization of spherical metal powders by microscope image analysis: a parallel computing approach

AbstractThe microstructural characteristics of spherical metal powders play an important role in determining the quality of mechanical parts manufactured by powder metallurgy processes. Identifying the individual powder particles from their microscopic images is one of the most convenient and cost-efficient methods for the analysis of powder characteristics. Although numerous image processing algorithms have been developed for automating the powder particle identification process, they perform less accurately in identifying adjacent particles that are heavily overlapped in their image regions. We propose an automatic algorithm to robustly and accurately identify spherical powder particles, especially heavily overlapped particles, from their microscope images. A parallel computing framework is designed to further enhance the computational efficiency of the proposed algorithm. Powder characteristics such as particle size distribution and the location of potential satellite particles have been derived from our identification results. The accuracy and efficiency of our algorithm are validated by real-world scanning electron microscope images, outperforming other existing methods and achieving both precision and recall above 99%.

Effect of the Ti-6Al-4V powder size on the microstructure and mechanical properties of composites with nickel-coated graphene nanoflakes

In this study, 0.5 wt% Ni-P@GNF/ Ti-6Al-4V composites with different particle sizes (0–25, 15–53 and 53–150 μm) were fabricated via chemical nickel plating and speak plasma sintering. The plasma sintering temperature and the sintering pressure were 900 °C and 50 MPa, respectively. The microstructure and mechanical properties of the three composites were investigated via optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and compression experiments. The results showed that the microstructures of the composites were refined, and the compressive strength of the Ti-6Al-4V incorporated with graphene nanosheets was higher than that of the pure Ti-6Al-4V. Herein, with 0–25 μm Ti-6Al-4V powder, the compressive strength of 0.5 wt% Ni-P@GNFs/TC4 composite reaches 1339 MPa, which was an increase of 37.91% versus Ti-6Al-4V alloy (970 MPa). Moreover, with increasing spherical powder particle size, the size of the reinforcing phase of the network structure was coarser, and the plasticity was improved. • Ni addition could decrease the interfacial reaction of composites. • The particle size was beneficial for grain refinement of composites. • The homogeneous dispersion of GNFs lead to load strengthening and network structure

Коррозионностойкие стали в аддитивном производстве

This review discusses the main methods for producing spherical powder particles of corrosion-resistant steels as a material widely used in all industries. Also the examples of products made by modern additive methods are described. Currently, spherical powder particles of corrosion-resistant steels are used in the following additive methods: selective laser melting, selective laser sintering, direct laser sintering, and electron beam melting. Each of these methods has its own requirements for the characteristics of spherical powder particles of corrosion-resistant steels. The review provides a brief description of the principles of operation of each method and the requirements for spherical powder particles of corrosion-resistant steels. It also considers a detailed description of each method of additive manufacturing with a description of the principle of operation and specific examples of obtaining spherical particles of corrosion-resistant steel powders with indication of their properties (morphology, structural features, chemical composition, fluidity, bulk density). A comparative analysis was carried out with a description of disadvantages and advantages of each method. Examples of the use of spherical particles of corrosion-resistant steel powders for the manufacture of products by various additive methods (including post-processing) are given with description of the final products characteristics. Based on the data presented, a conclusion was made about the preferred methods for obtaining spherical particles of corrosion-resistant steel powders for specific additive methods used in modern industry. The review considers the following methods for producing spherical powder particles: water atomization (atomization of liquid metal with a jet of water under pressure); gas atomization (atomization of the melt with a jet of inert gas (argon or nitrogen) under pressure); centrifugal atomization (atomization of molten metal with a high-speed rotating disc); ultrasonic atomization (atomization of liquid metal by ultrasound); non-contact atomization (atomization of liquid metal with a powerful pulse of electric current); plasma wire spraying; plasma spraying of a rotating electrode; plasma spheroidization.

Preparation of W-C-Co Composite Micropowder with Spherical Shaped Particles Using Plasma Technologies.

The possibility of obtaining composite micropowders of the W-C-Co system with a spherical particle shape having a submicron/nanoscale internal structure was experimentally confirmed. In the course of work carried out, W-C-Co system nanopowders with the average particle size of approximately 50 nm were produced by plasma-chemical synthesis. This method resulted in the uniform distribution of W, Co and C among the nanoparticles of the powder in the nanometer scale range. Dense microgranules with an average size of 40 microns were obtained from the nanopowders by spray drying. The spherical micropowders with an average particle size of 20 microns were received as a result of plasma treatment of 25.36 microns microgranule fraction. The spherical particles obtained in the experiments had a predominantly dense microstructure and had no internal cavities. The influence of plasma treatment process parameters on dispersity, phase, and chemical composition of spherical micropowders and powder particles microstructure has been established.

Study of mechanical spheroidization of powders obtained from waste metal shavings

This paper covers the search for a new method for generating metal powders for additive manufacturing. Raw materials for 3D printing are subject to certain requirements regarding the spherical shape of the powder particles, which are not easily met. The powder preparation methods used in the powder metallurgy may not be directly used for 3D printing without additional energy consumption for the spheroidization operation. More high-tech principles of melt dispersion shall be used for the spheroidization (atomization) of powder particles. Metal waste grinding in ball or vibrating mills generally yields plate-like particles, also requiring the use of energy-intensive atomization technologies. However, an analysis of related foreign research provided an alternative that is to use two-stage grinding to obtain spherical metal powder particles. Continued research in mechanical spheroidization enables the simultaneous manufacture and grinding of the required spherical particles while maintaining practically the same energy consumption that had been previously required for the grinding process. In order to form a research program and establish the optimal grinding size in terms of energy consumption and the dependence between the ball diameter and the grinding and spheroidization results for metal particles, respective preliminary experiments were carried out. The results of these experiments were then used to formulate the conclusions required to develop a method for establishing the optimal grinding ball charge level and composition. The study was carried out under the grant issued by the Russian Science Foundation (project No. 20-79-10125).

Powder Metallurgy Processing and Mechanical Properties of Controlled Ti-24Nb-4Zr-8Sn Heterogeneous Microstructures

This paper gives some insights into the fabrication process of a heterogeneous structured β-metastable type Ti-24Nb-4Zr-8Sn alloy, and the associated mechanical properties optimization of this biocompatible and low elastic modulus material. The powder metallurgy processing route includes both low energy mechanical ball milling (BM) of spherical and pre-alloyed powder particles and their densification by Spark Plasma Sintering (SPS). It results in a heterogeneous microstructure which is composed of a homogeneous 3D network of β coarse grain regions called “core” and α/β dual phase ultra-fine grain regions called “shell.” However, it is possible to significantly modify the microstructural features of the alloy—including α phase and shell volume fractions—by playing with the main fabrication parameters. A focus on the role of the ball milling time is first presented and discussed. Then, the mechanical behavior via shear tests performed on selected microstructures is described and discussed in relation to the microstructure and the probable underlying deformation mechanism(s).

Effect of gas pressure on conduit plasma atomization for fabricating spherical stainless steel powder

In this study, spherical stainless steel powders are produced using the conduit plasma atomization. Parameters of the conduit plasma atomization process with gas variations of 1.5 bar pressure, 2 bar pressure, 2.5 bar pressure with 316L stainless steel raw material with a current of 25 Amperes, feed speed of 2 mm3/s. The results of stainless steel powders were observed using a digital microscope (Dino-Lite AM4115), scanning electron microscopy (SEM-FEI-Inspect F50), and energy dispersive spectroscopy (EDS). To ensure the purity of the resulting 316L stainless steel spherical powder, EDS was used for qualitative and quantitative elemental analysis. The results showed that the 316L stainless steel spherical powder particles varied in size from 35 µm to 140 µm, making them ideal for powders metallurgy application. The effect of gas pressure on the powder weight percentages for particle sizes 50 µm – 100 µm for 1.5 bar pressure, 2.0 bar pressure, and 2.5 bar pressure were 67.14%, 78.71%, and 81.73%, respectively. It is possible that this could happen because to break down molten metal into smaller size droplets, it is needed the kinetic energy of larger gas pressure. So that large gas pressure can produce more small particle size compared to small gas pressure.

Fundamental principles of spark plasma sintering of metals: part II – about the existence or non-existence of the ‘spark plasma effect’

ABSTRACT The mechanisms of densification in spark plasma sintering (SPS) were investigated both analytically and numerically for a model system of two spherical metallic powder particles. From the microscopic temperature distribution, the possibility of a micro-local overheating of the particle–particle contacts was analysed for different particle sizes, contact geometries, materials, and electrical loads. It is shown that, for particles below the size of one millimetre, local overheating is below one Kelvin. Subsequently, the material transport by thermomigration, electromigration, and diffusion driven by surface curvature and external pressure was derived from microscopic field distributions obtained from analytical calculations and finite-element simulations. The results show that, while the mechanical pressure accelerates material transport by orders of magnitude, the electrical current and the temperature gradients do not. It is also shown that pulsing the current has no significant influence on the densification rate.

The possibility of obtaining spherical microgranules without satellites for surface-plastic deformation of responsible products

Problem. To strengthen the surface-plastic deformation (SPD) of components of a responsible purpose, for example, in the aviation industry, working bodies (microspheres) are used, which can be obtained by the technology of gas atomization. Powders used for SPD of machine parts must be spherical without satellites with maximum monodisperses. Goal. The aim of this paper is to develop a process for obtaining spherical microgranules without satellites in the process of gas atomization and to study the quality parameters of the surface layer of parts treated with the use of microgranules as SPD working bodies. Methodology. To obtain spherical microgranules it is proposed to use the method of gas sputtering of a metal melt with the use of a progressive rotating gas stream. In the proposed method, the destruction of the jet and the subsequent destruction of individual small particles occur in the vacuum, which is created by two opposite directed helical gas flows. This leads to the expansion of the crushing zone of the metal, reducing the direct impact of the gas on the liquid metal particles and, thus, allows the separation of the motion of small and large droplets in space, which significantly reduces the probability of the formation of small satellites on the surface of larger particles. Spraying of a metal melt of ShH15 steel, heated to a temperature of 1580 оС, was carried out at a gas pressure of 1,4… 1,7 MPa, a melt flow of 0,5 kg/s and a specific gas flow rate of 1,0 m3 /kg. Results. The efficiency of the application of the obtained working bodies is proved by the results of the study of the operational properties of the surface layer of the parts being processed: surface roughness corresponds RA = 0,9...0,8 μm; the degree of deformed state reaches 18...30% at a depth of up to 120 microns; the residual compression stresses are 300...700 MPa at a depth of up to 100 μm. Scientific originality. The factors that influence the number of satellites on the surface of spherical microgranules are analyzed in the paper. It is established that the organization of the rotation of the gas flow around the axis of the atomization in the radial direction facilitates the process of removal of fine particles beyond the sputtering torch, which, in turn, leads to a decrease in the number of satellites on spherical powder particles. Practical value. According to the tests, the use of microspheres of ShH15 steel for SPD of a wide range of parts, gives significant technical and economic advantages in comparison with other methods: elimination of costs for surface finishing after SPD; increased by 10...30 % endurance of processed materials; increased by 2...6 times the durability of parts; 3 times increased product life.

Production of Spherical Metal Powder for Additive Technology

A system is described for producing spherical metal powder (particle size 0.5–100 µm), with specified granulometric composition.

Production of a Functional Yogurt Powder Fortified with Nanoliposomal Vitamin D Through Spray Drying

In recent years, the problem of vitamin D deficiency has been echoed by extensive researches. Nutritionists believe that fortification of food products through this micronutrient is the best approach to solve this problem. In this study, properties of yogurt powders fortified with nano-liposomal encapsulated vitamin D were evaluated. The Taguchi method was deployed to design the treatments (16 runs) with 5 independent variables including temperature (160–190 °C), milk protein concentrate (0–3%w/w), modified starch content (0–3%w/w), gum Arabic (0–3%w/w) and maltodextrin (10–25%w/w), each at 4 levels. Dependent variables comprised of moisture content, solubility, colour and production (drying) yield. Analysis of our data revealed that the contribution order of different independent variables on responses was as follows: milk protein concentrate (30%), modified starch (28%), maltodextrin (22%), temperature (17%) and gum Arabic (3%). The average particle size of nano-liposomes containing vitamin D was about 120 nm. Also, SEM micrographs showed that addition of maltodextrin caused spherical powder particles with an even distribution in the matrix including yogurt and drying aids while incorporating milk protein concentrate, gum Arabic and modified starch brought about shrinkage as well as unevenness in the shape and size of powder particles.

The influence of powder properties on the adhesion strength and microstructural evolution of cold sprayed Ti6Al4V single splats

The adhesion strength and microstructure of single splats significantly influence the properties of cold sprayed coatings. Here, we compare the adhesion strength and microstructural changes of Ti6Al4V spherical powder (SP) particles with a martensitic microstructure and irregular powder (IP) particles with an equiaxed microstructure deposited by cold spray (CS). Splat adhesion tests were performed to determine the adhesion strength and electron channelling contrast imaging was done for microstructural analysis of splat cross-sections. IP splats formed a continuous bonded interface with the substrate resulting in a greater adhesion strength when compared to SP splats. IP splat cross-sections revealed ultrafine grains (UFG) near the interface followed by a highly deformed microstructure. SP splat cross-sections also showed UFG at the interface but largely retained the initial microstructure in the top portion of the splat due to poor deformability. The irregular morphology of the IP led to more adherent deposits while the equiaxed microstructure resulted in highly deformed post spray microstructures.

Preparation and characterization of spherical niobium silicide-based powder particles by electrode induction gas atomization

Nb-16Si-25Ti-8Hf-2Cr-2Al alloy powder was prepared by electrode induction gas atomization (EIGA). The Nb alloy ingot, which was prepared by vacuum arc melting and was subjected to solid solution treatment, was composed of a (Nb, Ti) solid solution and (Nb, Ti, Hf)5Si3. The grain size of each phase was larger than 50 μm. The ingot was gas-atomized using the EIGA process and sieved to the range of 45–75 μm. The spherical powder particles were manufactured successfully. The powder was composed of a (Nb, Ti) solid solution, (Nb, Ti, Hf)5Si3, and (Nb, Ti, Hf)3Si, and the silicide grain size was smaller than 5 μm.

A Taguchi approach production of spray-dried whey powder enriched with nanoencapsulated vitamin D3

The objective of the present study was to investigate the effect of inlet air temperature of spray drying and different combinations of carrier agents (maltodextrin (MD), gum Arabic (GA), modified starch (MS), and whey protein concentrate (WPC)) on the physicochemical characteristics of spray-dried whey powder, enriched with vitamin D3 to improve its usage as a functional ingredient. Firstly, vitamin D3 was nanoencapsulated by nanoliposome prepared with egg yolk lecithin, sesame oil, and glycerol through thin-film dispersion method. The mean particle size of prepared nanoliposomes was 140 nm. Then, the prepared nanocarriers loaded with vitamin D3 were added into the feed solution and dried through spray dryer. The effect of carrier agent types and inlet air temperature on the physicochemical (moisture content, solubility, porosity, color, and powder yield) and microstructure properties of obtained spray-dried powders were investigated. The optimal carrier agents and condition of spray drying were selected by Taguchi design. Our results showed that the inlet air temperature and carrier agent had significant effects on the characterization of powders. Powders produced by 2% WPC, 3% MS, and 25% MD at 170 °C inlet air temperature showed the highest powder yield (96.4%). Also, the morphology of powders was affected by carrier agent types; increase in MD concentration in feed solution causes to create smoother and spherical spray-dried powder particles.

Features of Amorphization of the Fe-TM-Nd-REM-B Alloys System at Melt Quenching by Gas Atomization

Gas atomization powders (GAP) chemical composition which corresponds to the first area of the phase equilibrium, and the fraction that ensures a cooling rate of a separate powder particle of more than 103K/s contains an amorphous component of two types: the first (AC1) has a chemical composition similar to that of the alloy; and the second (AC2) has a chemical composition of the triple eutectic. AC1 is mostly localized on the surface of the powder particles (in the form of layers, shells, nodules) or are detected in the whole volume of the spherical powder particles with its size less than 5 μm. The authors hold that during gas atomization, powder particles of this size have a cooling rate ≥ 105 K/s. Alloys having a similar chemical composition at similar cooling rates are also amorphized by quenching from the liquid state. This proves that an amorphous alloy of the first type is formed directly from a supercooled melt. While AC2 (enriched by Nd) is formed on the border or in the between the crystal phase Fe14Nd2B of the remaining (after primary crystallization during the primary phase) melt enriched by the moment of the solidification of Nd.

Melt Pool Analysis and Mesoscale Simulation of Laser Powder Bed Fusion Process (L-PBF) with Ti-6Al-4V Powder Particles

The laser powder bed fusion (L-PBF) process is accompanied by rapid melting and solidification that results in intense thermocapillary convection within the melt pool. Open-source particle simulation software was utilized to generate a single layer of spherical powder particles of variable diameter. Considering the importance of particle size and the particle size distribution (PSD) in the L-PBF process, three distinct categories of PSD were generated with identical settings. A three-dimensional (3D) thermofluid model was developed in this study, incorporating the generated layer of powder particles of nonuniform size over a thick substrate. A moving volumetric heat source was applied to melt a single track in the powder layer using a user-defined function in FLUENT software. Temperature-dependent material properties including variable surface tension were considered in the computation. The numerical model was used to simulate Ti-6Al-4V powder particles to observe the melt pool flow dynamics. Presence of particles of smaller diameter in the powder mix supported consistent and continuous melt pool flow, while any kind of void enhanced fluid convection in the downward direction, causing a temporal increase in melt pool depth.

Effects of Reusing Ti-6Al-4V Powder in a Selective Laser Melting Additive System Operated in an Industrial Setting

Cost control and quality of additive manufactured (AM) components are critical characteristics for the success of this technology for industrial applications. Understanding how the virgin powder changes in terms of chemistry and physical properties with reuse cycles provides important information that can be translated into cost-effective practices for managing recycled powder. In this study, we focused on an industrial AM setting, where different numbers of components were printed on each build. A single lot of powder was reused for manufacturing a total of 31 builds using a selective laser melting additive system. The effects of reuse cycles on the characteristics of Ti-6Al-4V extra low interstitial powder were evaluated, during and prior to the printing process, by means of particle size distribution, tap density, flowability, powder morphology, and chemical composition. Additionally, chemical analysis and tensile testing of solid bars in the hot isostatically pressed (HIP) condition were evaluated in relation to powder reuse times. After reusing the powder for 31 times, it was found that the oxygen content increased to a maximum of 0.13 wt.%, whereas nitrogen, aluminum, and vanadium remained stable. The powder exhibited surface coarsening, and although some elongated/irregular particles were observed, mostly spherical powder particles with fewer satellites were present. Flowability improved, and tap density showed a slight decline with reuse times. No detrimental effect was found on the tensile properties of solid material postprocessed using HIP.

Feasibility of Spray Drying Concentrated Acid Whey After Nanofiltration

Concentration of acid whey and crystallisation of lactose followed by spray drying in the production of acid whey powder are severely restricted by the presence of lactic acid (LA) and calcium (Ca). These compounds cause stickiness during spray drying. The present study examined the effects of removing LA and Ca by membrane processing to varying extents in order to improve the feasibility of the spray drying of an acid whey stream. Spray drying of unaltered acid whey achieved a powder recovery of ~ 18% in the collection vessel and ~ 31% in the cyclone. Removal of LA and Ca by 30 and 40%, respectively, by nanofiltration significantly increased the powder recovery to ~ 58% in the collection vessel. Powder particles decreased in size giving a D[4,3] of ~ 18 μm, with SEM images confirming the presence of well separated spherical powder particles. A solubility of > 75% was also achieved. However, removing Ca > 60% compromised the spray drying process. FTIR analysis suggested that water molecules in the hydration layer of lactose and the structural changes of both lactose and protein molecules at the molecular level appeared to play an important role in governing the extent of the drying feasibility. In addition, the formation of calcium lactate may restrict the diffusion of lactose molecules, once the appropriate stoichiometry was reached. Thus, manipulating LA and Ca concentrations in a particular acid whey stream can improve the spray drying process and production of a non-sticky acid whey powder.