Metal Powders For Additive Manufacturing Research Articles

New insights into the mechanism of ultrasonic atomization for the production of metal powders in additive manufacturing

Ultrasonic atomization is one of the promising technologies for producing metal powders for additive manufacturing, where precise control of particle size and morphology is essential. In this study, we coupled an ultrasonic transducer with a carbon fiber plate and atomized liquid droplets and films under different vibration amplitudes. Water, glycerol, and pure aluminum melt were used to study the atomization mechanism and the resulting droplet/powder characteristics, respectively. High-speed optical and ultrafast synchrotron X-ray imaging were used to study in situ the ultrasonic atomization dynamics, including pulsation and clustering of cavities inside the liquid layer/films, development of capillary waves, and formation of liquid droplets. For the first time, we observed and captured the occurrence of cavitation during the atomization of resting drops, films and impact droplets. The inertial cavitation events interfered with the capillary waves across the interphase boundary, puncturing and breaking the boundary to produce atomized mist. The in situ observation revealed the intricate dynamics of ultrasonic atomization and underscored the pivotal role of cavitation events throughout the entire atomization process. We also conducted experiments on ultrasonic atomization of liquid aluminum, producing particles of perfectly spherical shape. The particle size tended to decrease with reduced vibration amplitude Our work has demonstrated the important processing strategies on how to tailor the particle size while ensuring consistent particle shape and morphology, which is the key processing capability for producing high quality powders for additive manufacturing applications.

Solid-state production of uniform metal powders for additive manufacturing by ultrasonic vibration machining

This work presents a new technique to generate uniform and micron-sized metal powders for additive manufacturing. By collecting discrete chips resulting from ultrasonic vibration machining, we demonstrate the feasibility of all solid-state production consistent powders with tight dimensional tolerance, the ability to control powder geometry, and good efficiency. The technique offers a new route for sustainable and low-cost manufacturing of high-quality metal powders. The powder generation mechanism is analyzed with a special tool path design to ensure consistent dimensions over multiple cuts. An analytical model to predict the dimensions of produced powders under different cutting parameters is introduced. Aluminum and brass powders of different dimensions are produced, and the overall shear ratio that governs the deformation during the machining process is calibrated with the experimental results. The morphology consistency of produced powders is investigated over multiple hours of production, illuminating the role of tool wear on final powder shape. A high-efficiency powder collection system and a scalable solution for parallel production are proposed for the introduced technique. Additive manufacturing experiments (laser powder bed fusion) are conducted using produced A356 aluminum powders, demonstrating the printability of produced powders in additive manufacturing. The microhardness of the printed parts for five different process parameters is measured to be 45% higher than the raw material on average.

HIGH-SPEED VIDEO IMAGE ANALYSIS OF LIQUID METAL ATOMIZATION PROCESS

Gas-assisted atomization is used to produce metal powders for additive manufacturing. In these systems the primary atomization governs the powder size distribution, but it is experimentally challenging to investigate. In this study, the primary atomization of a molten metal spray was monitored with a calibrated high-speed camera and digital image processing. The technique enabled the generation of spatio-temporal maps at different distances from the nozzle. Among the characteristics of the spray, mean values and standard deviation of the spray width along the spraying direction, and the frequency of the oscillation of the spray boundaries are presented. Statistically relevant spray asymmetries were identified, which can be caused by faulty spray operation in form of a localized metal solidification at the pouring nozzle. By systematically varying the gas temperature and the gas atomization pressure, it is shown that heating of the gas up to 573 K stabilizes the spraying process and enhances the liquid dispersion in the recirculation zone.

Predicting the element loss in aluminum (AA2195) powder produced by gas atomization with a numerical model

Gas atomization (GA) is commonly used for making metal powders for additive manufacturing due to its efficiency and cost-effectiveness. However, the process results in the loss of low-boiling temperature elements like magnesium and lithium. These can negatively impact the performance of lightweight components of AA2195. To understand and address this issue, we used Inductively Coupled Plasma to compare the composition of ingots and powders produced by GA. The results showed a loss of around 20% of magnesium and lithium during the process. To investigated this symptom scientifically, we developed a numerical model based on evaporation theory. The simulation findings indicated that the loss of elements took place nearby the nozzle. Furthermore, it was observed that the utilization of powder with larger particle sizes resulted in a higher degree of element loss. Based on the results of simulation, we optimized the GA parameters and produced new powders that meet design criteria.

Ultrafine-bubble-water-promoted nanoceramic decoration of metal powders for additive manufacturing

The design of composite powders for exploiting the multifunctionality of metallic nanocomposites via laser additive manufacturing (AM) is challenging. Conventional ball-milling processes are prone to cause uncontrollable powder morphology and reduced flowability, while recently developed nanodecoration technologies are limited by complicated processing and impurity inclusion. Herein, a facile and scalable approach was developed using ultrafine bubble (UFB)-assisted heteroagglomeration to fabricate high-concentration, impurity-free nanoceramic/metal composite powders. Individual ZrO2 or Al2O3 nanoparticles up to ~10 wt% were homogeneously decorated on the surface of Ti-6Al-4V powders through the bridging effect of the negatively charged UFBs, leading to enhanced flowability and laser absorptivity. The nanoceramics were completely decomposed and dissolved into the matrix upon laser irradiation; therefore, a unique Ti nanocomposite exhibiting both high strength and ductility was obtained. Our work provides new insights into the application of UFBs and the fabrication of multifunctional AM components.

CFD Modeling of Primary Breakup in an EIGA Atomizer for Titanium Alloy Powder Production.

Electrode induction melting gas atomization (EIGA) technology is a commonly used and effective method for producing spherical metal powders in additive manufacturing. In this paper, we aim to describe the atomization and fragmentation of liquid sheets from a typical swirl nozzle and highlight the primary breakup of titanium alloy powder production. We developed a computational fluid dynamics (CFD) approach to simulate the primary disintegration process of the molten metal using the volume of fluid (VOF) method coupled with the large eddy simulation turbulence model (LES). Our numerical results show that high-speed spraying creates supersonic airflow in the atomization chamber. Recirculation is the main area where primary atomization occurs. The formation of the recirculation zone is the direct driving force that allows atomization to proceed, which will increase turbulence intensity and achieve higher atomization efficiency. VOF-LES simulation can capture some qualitative results such as conical melt-sheet shape, wave formation, ligament formation, and perforation formation. The primary droplet size mainly ranges between 200 and 800 μm. Finally, with increasing gas pressure, the particle size of the atomized powder gradually decreases, and the particle size distribution becomes narrower.

Understanding the breakup behaviors of liquid jet in gas atomization for powder production

Gas atomization (GA) is the main method to produce metal powders for additive manufacturing (AM) because of its low cost and high efficiency. However, the liquid breakup behaviors in high-speed gas flow during GA remains unclear, especially the primary breakup in the near field and the secondary breakup in the far field. Great difficulty exists in in-situ observation of the interactions between high-speed gas and high-temperature molten metal because of the limitations of the enclosed environment. Here, we built a new GA simulation system with a close-coupled atomizer utilizing liquids with low melting temperature, such as water, glycerin, etc. We use a high-speed camera to capture the evolution of liquid behaviors at various parameters. We first reveal that four primary breakup modes and four secondary breakup modes exist in the GA process, and these breakup modes significantly influence the particle size distribution (PSD) and the defects of the powder. Besides, the breakup modes are clarified by the dimensionless analysis. This manuscript provides an effective experimental platform to understand the breakup behaviors of the liquid jet in GA and suggests the optimal breakup mode for powder production.

An optical-based method to estimate the oxygen content in recycled metal powders for additive manufacturing

Powder recycling is key to enable sustainable and economically viable production of metal parts by fusion-based additive manufacturing (AM) processes. Determining the recyclability of a powder batch, however, requires continuous monitoring of the powder conditions during processing—notably the oxygen content—to avoid waste of resources while maintaining high build quality standards. In this work, we present a rapid and inexpensive method to acquire this information optically during the powder recoating step. Using a “powder bed scanner”, we capture high-resolution optical images of different powder batches and compute their relative oxygen content by assessing the colour of individual powder particles, which is a function of the surface oxide layer thickness. We compare these measurements against those obtained using conventional techniques and confirm that our method yields higher sensitivity and more consistent results. This work pinpoints a pathway to improving the recyclability of metal powders—at least of those which are heat-tintable—through continuous monitoring of their appearance during AM processes.

Self-assembly and in-situ characterization of Ti3C2Tx in Al: A step toward additive manufacturing of MXene-metal composites

Two-dimensional (2D) transition metal carbides, known as MXenes, have grown in research interest since 2011 partly due to their impressive high electrical conductivity, stiff mechanical properties, and abundant chemically-active surface groups. These key features of MXenes make them attractive candidates for uniform coverage of metal powders for additive manufacturing of multi-functional metal composites. In this study, we report on a tunable self-assembly process of nanometer-thick 2D MXene flakes on micron-size Al particles using 1–10 wt% of single-to-few and multi-layer Ti3C2Tx MXene. In addition, we discuss the characterization of these composites using 2D x-ray diffraction (XRD2) for identification of the characteristic Ti3C2Tx diffraction peaks. Lastly, we use in-situ XRD2 paired with Vickers hardness and scanning electron microscopy/energy dispersive x-ray spectroscopy methods to understand the effect of sintering on the Ti3C2Tx morphology and the resultant mechanical properties of the bulk composite. This study aims to assist future advances in additive manufacturing of MXene-metal composites for an array of multi-functional applications.

Absorbance study of powder conditions for laser additive manufacturing

Absorbance is often used for simulations or validation of process parameters for powder-based laser materials processing. In this work, the absorbance of 39 metal powders for additive manufacturing is determined at 20 laser wavelengths. Different grain sizes and aging states for: steels, aluminum alloys, titanium alloys, Nitinol, high entropy alloy, chromium, copper, brass and iron ore were analyzed. For this purpose, the absorbance spectrum of the powders was determined via a dual-beam spectrometer in the range of λ = 330 - 1560 nm. At the laser wavelengths of λ = 450 nm, 633 nm and 650 nm, the absorbance averaged over all materials was found to increase by a factor of 2.4 up to 3.3 compared to the usual wavelength of λ = 1070 nm, with minimal variations in absorbance between materials. In the investigation of the aged or used powders, a loss of absorbance was detectable. Almost no changes from the point of view of processing aged and new AlSi10Mg powders, is expected for laser sources with λ = 450 nm. The resulting measurements provide a good basis for process parameters for a variety of laser wavelengths and materials, as well as a data set for improved absorbance simulations.

Production of powders for metal additive manufacturing applications using surface grinding

Metal powders for additive manufacturing (AM) applications are commonly produced using atomization techniques, which are known to be expensive, capital intensive and highly inflexible. In this work, we explore an alternative route for producing metal powders by the use of surface grinding. We demonstrate the production of nearly monodisperse AISI 52100 steel powders for AM applications. The formation of these powder particles is analyzed using material characterization techniques. We then evaluate the usability of the produced powders for metal AM using a custom-built directed energy deposition setup. Post-process analysis of laser-assisted deposition tracks shows that our powders perform just as well as conventional gas-atomized powders, resulting in void and inclusion-free metallurgical bonding.

Effective thermal conductivities of metal powders for additive manufacturing

Effective thermal conductivities (ETCs) of five commonly used metal powders in additive manufacturing have been measured at temperatures up to 750 °C. The ETCs of Al-Mn-Sc and Ti-6Al-4V powders with different particle sizes are also investigated. When the temperature is lower than 300 °C, the ETC of metal powders is insensitive to the temperature and material. In contrast, when the temperature exceeds 400 °C, it increases significantly with increasing temperature and changes markedly dependent on the material. Additionally, in the lower temperature range, the larger size powders have higher ETCs, which is more pronounced for Al-Mn-Sc due to its higher thermal conductivity. In the higher temperature range, the larger Al-Mn-Sc powder shows higher ETCs than the smaller powder. In contrast, the smaller Ti-6Al-4V powder shows higher ETCs when the temperature exceeds 600 °C. The effects of temperature and particle size on ETC are investigated via particle morphology analyses.

Interaction between high-velocity gas and liquid in gas atomization revealed by a new coupled simulation model

Due to the high efficiency and low cost, gas atomization (GA) has been widely applied to produce metal powders. In this paper, the GA process is first modeled by combining the volume of fluid (VOF) model with dynamic adaptive mesh and the discrete phase model (DPM) to simulate the formation of the powders and the evolution of the defects. Simulation results show that the Kelvin-Helmholtz instability in the primary atomization and the membranous droplet breakup and closure in secondary atomization can form the hollow powder. While the presence of the satellite powder is caused by the collisions between the large and small droplets with different velocities. Moreover, the irregular powder is produced when the drag force is not enough to separate the droplets but deforms them. The estimated morphology and size distribution of the particles have a good agreement with the experimental ones. Finally, the possible measures to reduce the defects of the powders have been put forward based on the revealed mechanism of defect evolution. This work provides a deep simulation insight into the GA process, towards producing high-quality metal powders for additive manufacturing on a large scale.

Metal powders in additive manufacturing: A review on reusability and recyclability of common titanium, nickel and aluminum alloys

Metal additive manufacturing (AM) has received a lot of attention since its introduction, owing to its cost efficiency and freedom in design. For a successful and repeatable AM process, metal powders conform to strict chemical and physical properties requirements. There are numerous factors affecting these characteristics in both virgin and used powders. This article presents a comprehensive overview on manufacturing methods of AM metal powders and the reusability of titanium, nickel and aluminum alloys (mainly Ti‐6Al‐4V, nickel alloy 718 and Al-Si10-Mg) as well as criteria for such reuse. Moreover, the feasibility of recycling AM metal powders is discussed. This article also provides perspectives and recommendations for AM users to develop a well-defined and standard powder reuse process for consistent powder characteristics and built parts.

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).

Application of particle-size analysis in various industries

For various materials, rapid generation of results is always critical. Particle-size analysis of processing products using a laser-based particle-size analyzer is a valid alternative to the traditional sizing test. The article presents the results of studies conducted using Microsizer 201C equipment by the example of layered aluminosilicates and metal powders for additive manufacturing. The size analysis for these products is generally complicated by their ability to stick and agglomerate. Ultrasonic mixing does not harm the material analyzed and promotes uniform distribution of the sample during analysis. The results of granulometric analysis of kaolin ores obtained after different heat treatment are presented. The results of air-electric classification of metal powders obtained after vibration disintegration of metal chips are presented. The variety of raw materials shows a wide range of applications of this method in industry.

Intelligent System for the Efficient Classification of Metal Powders for Additive Manufacturing

Intelligent System for the Efficient Classification of Metal Powders for Additive Manufacturing

Reducing cohesion of metal powders for additive manufacturing by nanoparticle dry-coating

Additive manufacturing processes, such as laser powder bed fusion, require steady powder processing but often exhibit poor flowability and low powder bed densities. Reducing the attractive Van-der-Waals force through nanoparticle coating can enhance initially poor flowability. We investigated the effect of dry-coating nanosized SiO2 on gas-atomized CoCrFeNi powders containing different amounts of particles<20μm with respect to nanoparticle concentration and mixing time. The dynamic angle of repose of a 0–90μm powder reduced 50% and bulk powder density increased 30% with nanoparticle concentrations up to 0.153 wt.-%. The granular Bond-number was correlated with the powder flowability and porosity. The effect of mixing time was investigated with mixing two fractions 20–90μm and 0–90μm at a constant nominal nanoparticle surface area coverage of 128% for 2 to 1440min. Short mixing times improved the flowability, while extensive mixing resulted in nanoparticle reagglomeration and deteriorated flow.

Vibration technologies for producing metal powders

The history of application of vibratory devices for the processing of metal waste is considered. The report demonstrates the possibility of grinding metal waste generated in metalworking production on the example of iron-nickel and steel chips and of subsequent production of metal powders for additive manufacturing using the vibratory disintegration method. For the first time, the dependences of the main indicators of vibratory grinding of metal shavings on the degree of its mechanical processing were established, which made it possible to determine the specific energy consumption for the production of the required size classes. The regularities between the time spent on crushing metal shavings and power consumption during crushing are determined, which allows to detect the close relationship between energy consumption parameters and the physicomechanical properties of the chip, which makes it possible in the future to carry out a more detailed correlation of its physical and mechanical properties during disintegration.

Selective Laser Melting of Metal Powders in Additive Manufacturing

Selective Laser Melting of Metal Powders in Additive Manufacturing