PowderMet          AMPM          Special Interest

100 - Predicting Particulate Size Generation in Gas Atomization
Timothy Prost, Uniformity Labs, Inc

Current predictive models for powder size generation make many assumptions about atomization parameters, and for some conditions, the predicted value can be quite different than observed. Models published in the literature incorporate a generic characteristic length for the molten metal flow, often ascribed to the diameter of the pour tube orifice or melt stream diameter. However, these models do not typically incorporate more specific geometric data like apex angle, extension length, and gas jet configuration (e.g. close-coupled vs. free-fall, discrete jet vs. annular slit). In this study, these limitations and others are considered for a specific configuration of inert gas atomization; modifications to the models are suggested, and the resultant correlations are compared with observed values.

150 - Dynamic Statistical Visualization of Gas Atomization
Trevor Riedemann, Ames National Laboratory

A statistical visualization of the atomization process has been extended from a static image to a dynamic visualization.  Visual statistical representation of basic summary statistics for an image stack of high-speed video frames can be constructed via a z-project method. The result is a set of static images representing the average, minimum, maximum, median, and standard deviation of the pixel intensities with the image stack.  A sequence of such static statistical images can be used to reconstruct a video showing the statics evolving in time as the atomization progresses. The combination of standard video, high-speed video, and statistical visualization of the atomization process could serve to enhance human and machine learning operation of gas atomization. A technical methodology for real time statistical visualization is proposed. Work funded by USDOE-Advanced Manufacturing Office through Ames Lab contract DE-AC02-07CH11358.

106 - The Use of a Gas Flow Bench to Optimize the Performance of a Close-Coupled Transferred Arc Plasma-Wire Atomization Nozzle
Joseph Strauss, FAPMI, HJE Company, Inc.

The operation of the close-coupled transferred arc plasma-wire atomization nozzle consists of a plasma-generated plume of molten droplets radially surrounded by a secondary source of gas that is used to both propel and further atomize the contents of the plume. The secondary gas affects the plasma plume as can be seen from monitoring the stability of the operation and by measuring the particle size and distribution of the resulting powder. In order to investigate this effect, a flow bench used for quantifying the flow in conventional atomization nozzles was employed. By analyzing various trends, it was found that a close-coupled gas atomization nozzle was analogous to the plasma-wire nozzle. 

025 - Comparison of Compressibility and Compactability of Powders Based on a Piston-Equation
Gholamreza Aryanpour, University of Quebec Chicoutimi

Compressibility and compactability are two characteristics of a powder evaluated through a powder die compaction process. A piston-equation was previously introduced to describe die compaction of powders. The equation considers particle rearrangement and plastic deformation as two simultaneous mechanisms of densification from the beginning of compaction. The piston equation provides the possibility to calculate the contributions of rearrangement and plastic deformation phenomena in the material densification. This work describes how these contributions could be used to evaluate or compare the compressibility and compactabilty of different powders. 

018 - Strength, Fracture Toughness, Representative Defect Size and Stress Concentration Sensitivity, in Powder Compacts
Joseph Wright, Drexel University

The characterization of the green strength of powder compacts is commonly performed using bending tests and diametrical compression tests. This classic approach provides only a limited insight into the defects that limit the strength of the compact or the inherent fracture toughness of the compacted material.  In this work we reexamine some early work on the reduction of strength due to a stress concentration (a hole in this case) using modern concept of fracture mechanics.  As a result of this approach, we are able to obtain both the fracture toughness of the compact and the size of the representative defect for brittle compacts.  The usefulness of the latter can be easily demonstrated with its correlation with the average particle size.  This methodology uses simple die shapes (round or square with and without a hole).  In addition to a broader characterization of the compact, these experiments provide interesting insight into the observation that powder compacts are less sensitive to the presence of stress concentrations (notches, holes etc.) than the corresponding wrought parts. The work presented here is documented using experiments on pharmaceutical powders but the concept is fully application to brittle compacts from metallic powder also.

191 - Realization of S-N Woehler Fatigue Data of High Statistical Evidence and Its Conversion into FKM-Conforming Fatigue Data Sets
Markus Schneider, GKN Powder Metallurgy Engineering GmbH

Fatigue experiments are time consuming and expensive. Therefore, careful planning regarding the needed fatigue testing specimens and the corresponding statistical evaluation is needed. In contrast to other industries (for instance the forging or the casting industry), the production of compacted and sintered fatigue testing specimens is not related to high machining costs if the as-sintered surface is accepted as representative of typical surface conditions. As a consequence, the statistical scatter of S-N Woehler data, the material’s high cycle fatigue (HCF), and long-life cycle fatigue (LLF) behavior can be evaluated without extra effort. In general, the German FKM-guideline requires several model parameters to approximate material response in terms of mean stresses, stress concentrations, process influences, and scatter. This paper shows GKN Powder Metallurgy’s current way of fatigue testing and provides step by step instructions for analyzing the fatigue data and converting it into the fatigue data sets used with the FKM-guideline.

088 -Advantages of Paste Feedstock over Loose Powder in Sinter-Based Additive Manufacturing Applications
Ben Arnold, Tritone Technologies

As Metal Binder Jetting continues to gain attention in new metal AM processes other technologies are available and offer important advantages.  This talk will highlight an emerging technology called Moldjet and will focus specifically on the use of paste feedstock and the advantages this brings to prospective users.
We will share the technical basis for how paste enables a wide range of particle sizes and morphology and improves density variation in green parts. Additional operating advantages in part post processing will also be explored.  Results of ongoing data collection across a number of experiments will be shared highlighting mechanical properties and dimensional results across varying part orientations, build locations, and material lots.   

156 - Analytical Methods for Reducing Binder Saturation Variation in a Sinter-Based Additive Manufacturing Technology
Midhun Gopakumar, 3DEO, Inc.

Research shows that binder saturation directly affects a variety of properties of AM parts in both green and sintered states. Properties such as sintering shrinkage, green part strength, debinding, and sintering densification are among the most important ones that define the quality of the final product. Therefore, it is beneficial to increase the uniformity of binder saturation across every printed layer. In this research, a proprietary test method was used to measure binder mass per unit area at various independent X-Y locations on the print bed. The scope of this study is to explain the statistical techniques and analysis of the test data performed in order to reliably choose the most suitable binder delivery design, minimizing binder saturation variation. The analysis led to a design that produced a more repeatable and uniform binder distribution in a printed layer that follows a Gaussian distribution.

173 - X-Ray Computed Tomographic Study of Density Gradients within Binder Jetting and the Influence of Printer Design and Printing Parameters on Ballistic Ejection
Jacob Feldbauer, Penn State University DuBois

Binder Jet Additive Manufacturing (BJAM) is a versatile powder bed technique that uses a binder deposited using ink jetting to form complex components. Ballistic ejection occurs during the application of the binder to the powder bed layer during the binder jet printing process.  The momentum of the binder droplet impacting the powder bed results in a disturbance of the powder layer.  This disturbance of the particles in each layer causes inconsistencies in the density and bonding during the sintering step of the process, resulting in a localized disruption in the uniformity of the material properties.

The printer design and the parameters used to print influence the size and momentum of the binder droplet.  The influence of these parameters will be reviewed to minimize ballistic ejection during printing and improve the quality and uniformity of the printed components. We use X-Ray computed tomography to study the differences in 17-4 steel parts as printed in the green state. This information will be critical for understanding the evolution of inhomogeneity in sintered components and their role in material properties. 

124 - High-Purity Spherical Tantalum for Additive
Abraham Calvin, Global Advanced Metals

Emerging applications in the energy, defense, and medical sectors are pushing the boundaries of conventional materials and processes, requiring technical advancements to achieve novel requirements.  Refractory metals, such as tantalum and tantalum alloys, in conjunction with additive manufacturing processes, are playing a pivotal role in rising to these new challenges by enabling high-temperature performance, biocompatibility, and ductility.  To achieve the highest possible performance, metal purity and quality must be maintained from raw material through to the final product.  By meticulously controlling the powder manufacturing processes, high-purity refractory metals can be consistently produced ensuring sustainable success in the additive manufacturing of a wide range of devices.

This presentation will highlight high-purity tantalum powders developed for a variety of AM technologies.   It is imperative that AM powder handlers and producers understand the various powder production processes to better design and define the material capability.  Through a better understanding of the process limiting factors and elimination of impurities such as oxygen, nitrogen, and carbon, it is possible to generate performance-optimized tantalum and other refractory powders, while also minimizing material yield loss to reduce material costs.  Tantalum powders manufactured with these considerations have and will be shown to be fully compatible with all additive technologies delivering high fidelity, fully-dense components with the potential of achieving mechanical performance on par with wrought material.

170 - Plasma Gas Atomizer for Refractory Metal Alloys in High Temperature Applications and Harsh Environments 
Aamir Abid, Retech Systems LLC.

There is an increase in demand for refractory metal alloy powders using additive manufacturing modalities. To improve the overall efficiency of gas turbines, high-quality refractory metal alloy powders are required in pilot or production scale quantities.  High-temperature alloys are also required to solve corrosion and thermal stability challenges in renewable energy applications. Current powder production methods are not suitable to produce such powder as the process requires an engineered feedstock such as rod or wire. Many alloy systems of interest are either too brittle to form rod/wire (for example, refractory high entropy alloys) or have a complex chemistry that is not commercially available.  Retech has developed an atomization system that provides a larger production capacity for a range of metal and alloy powders utilizing Plasma Arc Melting (PAM) in combination with gas atomization. Plasma melting allows for the introduction of a broad range of feed materials including revert without incurring the additional cost of processing feed to wire or bar forms. With this flexibility of feed materials, recycling high-value materials become an economically viable option. The powders produced on the Plasma Atomizer are spherical with minimal satelliting and low internal porosity. Refractory metal alloy Particle Size Distribution (PSD), morphology, and chemistry will be presented in this study.

009 - Cost-Effective Manufacturing of Metal Powders through Continuous Process by SMS Group
Tobias Brune, SMS Group GmbH

SMS group supplies plant technology for the production of high-quality metal powder for Additive Manufacturing (AM) and other technologies. Cost-effective and high-quality powders will be one of the main drivers for the development of metal AM towards a sustainable industrial technology. By operating a gas atomization plant (VIGA - Vacuum Induction Gas Atomization) integrated in the SMS 3D-Test Center, the SMS group has optimized the classical powder production for the requirements in AM over the last years.
In addition to conventional gas atomization plants, the SMS group, together with a customer, has developed another innovative powder production process. The conventional batch-wise process is transformed into a continuous process. The continuous powder production plant enables cost-effective and large-scale production of up to 4,000 tons per year. Compared to the traditional gas atomization process the capacity is increased by a multiple. Production costs for spherical, high-quality metal powders are significantly reduced. The increase in capacity results in enormous economies of scale. Set-up times, melting and cooling times are reduced. In the new process developed by SMS group, two Vacuum Induction Melting (VIM) furnaces continuously hold liquid melt, which is atomized successively through the nozzle. The nozzle can be exchanged during operation. Melting is done under vacuum to guarantee highest quality levels like in the conventional process.

083 - A Computer Vision Approach to Predict Powder Flowability for Metal Additive Manufacturing
Mahdi HabibnejadKorayem, GE Additive

Additive manufacturing (AM) is a transformative technology to many industries that enables the fabrication of parts with complex geometries. For the AM techniques using powder feedstock, powder packing behavior and flowability significantly affect the defect density, such as porosity, and eventually the reliability of as-built parts. Experimental characterization of these powder properties, such as Hausner ratio, Carr index, and angle of repose, is rather time consuming and cost inefficient. Here, we show a fast, low-cost, and reliable computer vision approach to predict powder flowability. We employ seven machine learning models to “learn” from the 2,000 scanning electrons microscopy (SEM) images of 16 types of powders commonly used in metal additive manufacturing. Our results indicate that the vector of locally aggregated descriptors (VLAD) model with speed up robust features exceeds by about 12% mean absolute percentage error (MAPE) value, which is at least 3% lower than traditional convolutional neural network model. The performance of all the models is robust to the changes of image brightness and contrast. This result verifies the established computer vision model can predict the flow properties of metal powder that does not exist in the dataset. Our study demonstrates that the computer vision approach is a powerful tool to automatically analyze powder flow properties, providing a new opportunity to inspect and evaluate the flowability for the powders used for AM.

041 - Powder Feedstock Characterization for DEM Simulation of Laser Powder Bed Fusion
Guohong Xie, McGill University

The laser powder bed fusion (LPBF) process contains several steps including powder preparation (feedstock), powder spreading and laser printing. In LPBF, the quality of the powder feedstock is of great importance. In general, fine, and spherical powders are typically used but are more expensive. A better understanding of the powder and the powder flow behaviour is required to minimize defects from improper usage of the powders. The discrete element method (DEM) provides a particle-scale approach to simulate the motions of the powders that can be used in LPBF. But to maximize the reality of the simulation, appropriate characterization of powder properties is paramount. The current presentation compares the properties of AA5056 and CPAL powders with three particle size distributions. Shear interaction tests with the FT4 apparatus and drop tests with a high-speed camera were used to determine the coefficient of static friction and the coefficient of restitution. The results show that the CPAL powders have a higher coefficient of friction than AA5056. The results from rotating drums indicate that the CPAL powders are more cohesive than AA5056, and finer powders have larger cohesion. These results are used in DEM simulations involving powder spreading.

065 - The Recycling of Water Atomized Tool Steel Powders Used in the Laser Powder Bed Fusion Process
Denis Mutel, Laval University

The production of parts by laser powder bed fusion (LPBF) involves the input of a large amount of energy to the powder bed in the form of a highly localized laser beam. The creation of a melt pool unfortunately leads to the projection of liquid droplets on neighboring particles, which can eventually compromise the quality of the powder and therefore its reuse for future prints. This phenomenon is particularly critical for water atomized powders that have fewer regular particles than those fabricated by gas atomization. The successive utilization of a same powder lot, including cleaning after each use, also has the effect to change the rheological properties. For obvious economic reasons, the recycling of powders is a subject of high interest, that if coupled with the production of LBPF feedstock by water atomization, would greatly contribute to drive down the costs of LPBF. The work summarized in this manuscript studies the variation of the rheological properties, the particle size and shape distribution as well as the chemical composition throughout multiple reuse cycles in LPBF of water atomized too steel powders.

027 - Material Extrusion 3D Printing Using Low-Viscosity MIM-Like Feedstocks
Vincent Demers, École de Technologie Supérieure

Material extrusion (MEX) 3D printing is an additive manufacturing process that has become particularly interesting for manufacturing metal parts. This relatively recent process now uses high solid loading powder-binder mixtures similar to those used in MIM to fabricate layer-by-layer green parts that are finally debound and sintered to obtain dense metallic parts. This communication aims to present a novel 3D printer developed to print low-viscosity MIM-like feedstocks and quantify its performances in terms of printability, defects occurrence, and dimension accuracy. Using high solid loading (64-66 vol. % of powder) but low-viscosity feedstocks, it will be shown in this paper that the typical and almost unavoidable interlayer defects can be completely eliminated, therefore producing fully dense green parts. Because no extrusion flow multiplier technique, this intrinsic advantage linked to the rheological properties of the powder-binder mixture will also guarantee precise component dimensions. Finally, 17-4PH powder will be blended with paraffin wax, stearic acid, and different proportions of ethylene vinyl acetate to design a printable feedstock that will be printed, debound, and sintered to obtain monotonic mechanical properties of this new fabrication approach that will be benchmarked with MIM.

004 - Detection of Defects in Parts Produced by Material Extrusion 3D Printing Using In-Line Pressure Measurement
Raphaël Côté, École de Technologie Supérieure

Material extrusion (MEX) of highly-filled polymer is a metal additive manufacturing process that has received increasing interest over the past 3-5 years for its ability to produce dense metallic parts with complex shapes. In this process, a metal powder is mixed with a polymeric binder to produce a MIM-like feedstock that is extruded in a FFF-like process to 3D print green parts. The latter is then debound and sintered to produce a dense metallic part. Although present only in small amounts, air trapped in the molten feedstock may produce sub-millimeter size voids in the printed parts that are still present after sintering, resulting in a decrease in the part density and so in its mechanical properties.  In this work, a new plunger-based 3D printer design was equipped with a load cell to measure the printing pressure and detect pressure variations due to air trapped in the feedstock. In addition to validate printing pressure obtained by numerical simulations, the experimental pressure profiles were suitable to detect variations in pressure corresponding to punctual and sudden changes in flow rate due to the extrusion of air bubbles. X-ray tomography analysis confirmed the sudden changes in pressure detected using this in-line extrusion pressure technique was originated by the presence of voids in the defective printed parts. The printer presented in this paper therefore offer a new low-cost and in-line tool for the real-time detection of defects in green parts, avoiding post-printing analysis. 

049 - Development of an Aluminum-Based Feedstock for Material Extrusion 3D Printing
Dorian Delbergue, École de Technologie Supérieure

Material extrusion (MEX) of metallic feedstock has received an increase of interest over the past 5 years. In this additive manufacturing process, a mixture of sacrificial polymeric binder is highly-filled with metallic powder (similarly to those developed for metal injection molding) and then printed layer-by-layer to shape a green part. The latter is then debound and sintered to remove the binder and densify the final metallic part. The quantity and occurrence of adhesion defects and voids, which are the major drawbacks of the MEX process, can be minimized or avoided by controlling the feedstock viscosity. As many aluminum alloys can be difficult to print using laser powder bed fusion (L-PBF) and the productivity is still rather limited with L-PBF, MEX process becomes an interesting alternative to fabricate complex-shape aluminum parts. However, such kind of aluminum-based powder-binder mixtures are simply absent from the market or scientific literature. This study aims to develop aluminum-based (AlSi10Mg) feedstocks used in MEX 3D printing. First, rheological analysis will be used to correlate the feedstock viscosity with its printability. Then, 3D printing will be performed using a laboratory plunger-based printer. Finally, Archimedes density and SEM observations will be performed to quantify the performances of such aluminum-based feedstocks.

510 - High Purity Tungsten Powder – Achieving Five Nines
Tyler Showalter, Buffalo Tungsten

Conventional methods of tungsten powder reduction achieve a purity of 99.99%. For some industrial applications, a higher purity material is desirable. A tungsten content of 99.999% can be achieved with high purity raw materials using special production methods and material handling. An overview of the equipment and procedures will be presented. A review of laboratory methods for detecting impurities at this level will be given. Assay results for high purity material will be compared to the purity of tungsten powder produced with standard methods. An examination of current industrial applications for high purity tungsten powders will be offered.

511 - Understanding Refractory Metal Thermocouples at 350–2,315 °C
Todd Leonhardt, Rhenium Alloys

Rhenium Alloys Inc. performed a comprehensive metallurgical study of the chemical, physical, and electrical properties of ultra-high temperature type C thermocouples (tungsten 5% rhenium/ tungsten 26% rhenium (by weight) wires). All thermocouple components (wire, ceramic insulators, and molybdenum sheath were examined with optical microscopy and scanning electron microscopy- energy dispersive spectroscopy before and after elevated temperature exposure in a hydrogen atmosphere.  An evaluation of temperature measuring techniques was performed for type C thermocouples versus an optical pyrometer to understand the limitations of both temperature measuring systems. Finally, we will discuss the potential of a new type C thermocouple that is stable at temperature beyond 2,200°C. 

512 - Additive Manufacturing of Tungsten-Copper Bi-Material Structures for Plasma-Facing Component Applications in Fusion Devices
Robert Lürbke, Max-Planck

In future magnetic confinement fusion reactors, so-called plasma-facing components (PFCs) have to sustain high heat flux loadings and intense neutron irradiation reliably. These harsh operating conditions create the need for the development of corresponding advanced materials and component solutions. Tungsten is currently considered the preferred directly plasma-facing material in fusion devices due to its low hydrogen retention as well as its low physical sputtering yield. Apart from that, tungsten-copper (W-Cu) composite materials are currently of interest as advanced high-temperature heat sink materials for highly loaded PFCs. In this context, additive manufacturing (AM) of W can be regarded a potentially useful tool as it provides a way to realise W parts and preforms for composite structure fabrication with a high degree of design freedom. Hence, this approach opens up new possibilities to realise W-Cu composite structures, e.g. with tailored macroscopic thermophysical/-mechanical properties. However, the AM of W is challenging, due to the properties of W which is an intrinsically brittle refractory metal. Against this background, the contribution will summarise topical results regarding the AM of W by means of laser powder bed fusion (LPBF). This will include results of parametric fabrication studies, including the fabrication of delicate lattice-type parts as well as tailored W-Cu interface structures. Apart from that, results regarding the multi-material AM of W and a copper alloy (CuCrZr) will be presented focussing on microstructural analyses.