PowderMet AMPM Tungsten Special Interest
SESSION P09 Water-Atomized Powder Development
043 - A Lab-Scale Water Atomizer to Produce Metal Powder: Flexible Design for Parametric Study and Visualization
Ali Asgarian, University of Toronto
Water atomization is a cost-effective method for producing metal powders. Though relatively mature, this method is yet to be optimized for producing finer powders suitable for advanced powder metallurgy (PM) techniques, e.g. metal additive manufacturing (M-AM) and metal injection molding (MIM). In order to optimize operating and design conditions, one needs to understand the phenomena involved in water atomization and performs parametric studies. Visualization is an important route to understand the phenomena, but it is impossible at full scale due to the harsh environment. So, we have built a lab-scale water atomizer. We present the design of lab-scale water atomizer representative of an industrial metal powder plant. This setup was designed with two objectives in mind: flexibility for changing design and operating conditions, and to allow high-speed shadow imaging. A low-melting point metal alloy was water atomized at different operating and design conditions, thanks to the flexible design.
089 - Optimization of Water-Atomized Tool Steel Powders for Utilization in Direct Energy Deposition (DED) and Laser Powder Bed (LPB)
Denis Mutel, Laval University
The vast majority of powders used in additive manufacturing (AM) are obtained by gas atomization. This process allows producing spherical particles that are exempt of significant oxidation. The objective of the work summarized in this manuscript is to substitute gas atomization with water atomization to produce A8 and S7 tool steel powders. The idea is to optimize the water atomization process and the chemistry of the original alloys to maximize particle regularity (morphology) while minimizing oxygen content. Thus, tool steel powders adequate for additive manufacturing could be produced at a fraction of the cost of gas-atomized tool steel powders. Following hydrogen reduction, the water-atomized powders were used to fabricate parts by Directed Energy Deposition (DED) and Laser Powder Bed (LPB). Test specimens were characterized in terms of their microstructure and tensile properties and results were compared to those measured with specimens manufactured with gas-atomized powders.
179-R - Relationship Between Segregation and Powder Handling System Design
Mursal Ashrafi, Jenike & Johanson, Ltd
Powder uniformity is key to achieving consistent quality in manufactured parts and reliable operation in powder metallurgy (PM) processes. Maintaining a uniform blend throughout the process can be challenging if the powder handling system has not been designed to avoid segregation. Segregation in PM processes is a function of particle size distribution and physical properties of the powder as well as the type of handling equipment used. It is also a function of the entire process flowsheet. Depending on the properties and equipment design, the mechanism of segregation can be different. In this paper, primary mechanisms of segregation observed in PM processes will be discussed as well as the relationship between equipment design and segregation tendency of powders. This relationship will be illustrated by going through an example process flowsheet encompassing all general PM process steps to understand how segregation occurs at each transfer point.
SESSION P10 Secondary Operations and Dimensional Control
122 - Dimensional Change and Distortion of Heat Treated Components from PM Copper Steels Containing Various Carbon Content, and being Subjected to Post-Sinter Impregnation by Inorganic Sealant
Leonid Frayman, Allegheny/Pamlico Coatings
Powder metallurgy (PM) components formed from MPIF standard copper steels are widely used for a variety of structural applications due its excellent balance of mechanical properties, relative processing simplicity for high volume production and low fabrication cost. Within industrial practice, optimal functional and operational properties expected for components from the referenced PM steels, are achieved through the as sintered state or through heat treatment (HT) by rapidly quenching from the austenitic phase towards forming martensitic phase followed by a subsequent tempering. During HT processing and associated intensive cooling, heterogeneous metallurgical phase changes, density gradients (residual porosity) and carbon chemistry distribution can often lead to measurable distortion and size variation of the hardened components. The carbon chemistry distribution within the HT PM copper steels is dependent on the initial powder carbon content as well as on the carbon potential of the HT furnace atmosphere and specifics of copper and carbon diffusion within the iron matrix. For example, per the ternary iron-copper-carbon phase diagram, the solubility of copper in austenite at a sintering temperature 1050oC is 7.5wt%, is varied to 5.5 wt% at the austenization temperature (900-925°C), and then becomes almost negligible within the iron ferritic matrix at room temperature. The variation of copper solubility during HT along with carbon diffusion are significant contributing factors to dimensional instability and can have a negative impact on dimensional process capability.
032-R - Evaluation of Consistency in Machining of PM Components Produced with Common Copper Steels
Cody Kalinoski, Engineered Sintered Components
The powdered metal (PM) industry continues to experience growth in the area of machining due to increasing geometric complexity and tolerance requirements of PM parts. The PM manufacturing process allows for a wide range of chemistries and additives that yield the desired mechanical properties and machinability.
One of the most important alloying elements in PM is carbon, which is added to PM mixes in the form of graphite. During the sintering process, carbon atoms diffuse into the iron matrix, transforming it into a sintered steel part. The diffused carbon level directly influences microstructure formation and the hardness of the matrix. The microstructure formed, as well as its hardness level, directly affect the mechanical properties and machinability of the component. Previous studies on simple components have shown that the relationship of sintered carbon content and the amount of proeutectoid ferrite in copper steel have a significant effect upon the machinability of the component. It was found that inconsistent machining occurred easily between 0.75%C and 0.80%C due to the formation of proeutectoid ferrite within the microstructure. This paper will look to translate laboratory testing results to actual production practices in order to determine which carbon level provides more consistent machining in production settings.
010 - Evaluation of the Dimensional Change and Distortion After Heat Treatment of PM Components, being Subjected Post-Sinter Vacuum Impregnation by Inorganic Sealant
Leonid Frayman, Allegheny/Pamlico Coatings
PM steels that are rapidly quenched from the austenitic phase to form a martensitic phase at a heat treatment (HT) hardening process, exhibit, to some degree, unavoidable distortion or dimensional changes. Prime factors leading to the distortion include creep phenomena at high-temperature soaking of the austenitizing temperatures, contraction during intensive cooling due to volumetric differences between the austenite and martensite microstructural phases, and inherent residual porosity in the PM steels with associated shrinkage phenomena. Thermal gradients during the quench process and residual strain fields within the hardened PM structure may also contribute to distortion and to dimensional changes within the PM components. All these factors can provide a cumulative effect within the PM components microstructure resulting in internal stresses, which can become large enough to exceed the yield point of the material, hereby leading to permanent plastic deformation. However, some negative effects of distortion and size change can be mitigated with the utilization of vacuum impregnation by inorganic sealant, being applied at a post-sinter stage into the PM components prior to the HT hardening process.
SESSION A10 AM Modeling II
209 - Creep Modeling of 3D Printed Nickel Based Superalloy
Harshal Ghanshyam Dhamade, Indiana University - Purdue University Indianapolis
The objective of this research is to better understand and advance the knowledge of creep behavior of Nickel Alloy 718 manufactured through Selective Laser Melting. A finite element model with subroutine is created for simulating the creep mechanism for 3D printed Nickel Alloy 718 components. Using a multi-regime creep model, such as the Kachanov-Rabotnov model, the model is capable to simulate the secondary and tertiary creep behaviors. Specifically, a continuum damage mechanics (CDM) approach is employed by a user-defined creep subroutine formulated to accurately capture the creep mechanisms in the alloy. Using a calibration code for the material constants, a creep rupture prediction model is created to simulate the creep test. The model developed in this work can reliably be used to predict creep behavior for 3D printed metals under uniaxial conditions.
085 - Lattice Structure Design for Metal Fused Filament Fabrication (MF3) of Ti-6Al-4V
Mohammad Qasim Shaikh, University of Louisville
This study investigated the additive manufacturing (AM) of Ti-6Al-4V using metal fused filament fabrication (MF3) process to design and fabricate lattice structures. Metal-polymer feedstock with a solids loading of 59 vol.% was compounded and extruded into a filament which was 3D printed into lattice structures. The influence of printing process parameters and lattice geometry on dimensional variation and defect evolution were investigated. In addition, the sensitivity of dimensional fidelity of the lattice structures to material composition was studied. The printed lattice structures were characterized for relative green density, residual stresses, deflection and warpage and compared to predictions. Defect-free green parts were debound and sintered to examine dimensional change, properties and shape preservation following thermal processing. The outcome of the work is an understanding of geometry-processing-material inter-relationships governing the design and fabrication of lattice structures by MF3.
244 - Factors Affecting the Dimensional Variation in SS 17-4 PH Binder Jet Components
Mukund Nagaraj, INDO MIM INC.
Additive manufacturing processes have provided an avenue to manufacture metal components with highest complexity and customized geometries. Although they are currently being utilized for low-volume production especially for tool making and prototyping, some of these processes are moving towards mass production, specifically the Binder Jetting (BJT) process which is relatively more scalable to mass production. At higher volumes, there will be dimensional variation in parts that are induced by the printing and as well as the subsequent processes.
This paper aims to study the factors influencing the dimensional variation of SS17-4 PH parts printed using a binder jet printer. Test specimens with different geometries will be printed across the build-box at different conditions and the variation in dimensions will be reported upon necessary post-printing processes like curing, depowdering, debinding and sintering. In addition to charting the sintered dimensional variation from the print location, the green condition variation will also be tracked to correlate its effect on sintered dimensions. The results from this study should also help in establishing critical process variables in the binder jet process and derive an estimate of the dimensional tolerance that can be achieved.
SESSION A11 AM Powder Production I
215 - Microstructure and Mechanical Response of Bulk Nanocrystalline Cu-Ta Alloys Consolidated from Cryomilled Powders
Anqi Yu, University of California, Riverside
There has been growing research interest in nanocrystalline (NC) materials due to their superior strength as compared to their coarse-grained counterparts. However, most NC materials suffer deleterious grain growth at low homologous temperatures or under mechanical loads. Recently, it has been shown that certain immiscible systems, such as Cu-Ta, can retain NC grains under these circumstances. The lack of miscibility, however, makes attaining these microstructural features require processing techniques that drive non-equilibrium states. In this study, NC Cu-Ta alloys are achieved by cryomilling and Spark Plasma Sintering (SPS). The fabricated product shows that although the refined Cu grain size grows slightly after SPS, they are still nanoscale in dimensionality. Further, the microscopy results are combined with the mechanical testing to discuss the predominant strengthening mechanisms in this study.
027 - The Production of High-Grade Metal Powder for Additive Manufacturing
Elise Rowe, SMS group GmbH
By understanding the different influencing factors during atomization and the influence of powder properties on the additive manufacturing process SMS group is able to produce powder with improved quality and increased output. To realize highest cleanness of the powder during production, the melting and refining of metals and alloys takes place under vacuum or inert gas atmosphere. The atomizing process, using the close-coupled principal, guarantees defined grain sizes and distribution of metal powders. A high spherical morphology of the powder particles is requested during laser powder bed fusion to guarantee good powder flow properties. By the operation of an anti-satellite system in the powder atomization plant at SMS group powder of highest sphericity can be produced.
There is currently another presentation (student) in that spot which will have to be moved so don’t delete Anqi Yu’s information.
177-R - Low Alloy Water-Atomized Steel Powder to Produce Pump Parts Using LPBF
Amin Molavi Kakhki, Rio Tinto Iron and Titanium
Low cost water atomized (WA) powder as feed material for laser powder bed fusion (LPBF) additive manufacturing (AM) can reduce manufacturing cost significantly. To verify the effect of WA powder on AM, a WA low alloy steel powder, was developed specifically for AM and its performance in AM was tested at KSB. Various samples were printed to study the effect of scan speed, layer thickness and hatch distance on surface finish and relative density of the printed samples. Results showed that a combination of printing parameters can result in 99.2% or more relative density. Furthermore, tensile test bars were printed using the optimum printing parameters and then heat treated. Mechanical properties measurements showed that the printed and heat treated samples have equivalent mechanical properties to the standard grade (ASTM A105, DIN 1.0460). The results were used to produce pump parts which are presented in the paper.
SESSION A12 Metal AM Build Processes I
025 - Evaluation of AM Technologies in MIM Applications: Part II
Joseph Tunick Strauss, FAPMI, HJE Company, Inc.
This study investigated the feasibility of producing a MIM-like part via metal AM technologies, specifically Binder Jetting, Material Extrusion, Metal Jetting, and Photopolymerization of metal-loaded photopolymers. These new AM technologies are of interest to MIM companies as they leverage much of the knowledge base of MIM and, in some cases, use similar powders. These AM technologies have the potential to enable the production of MIM-like parts at production volumes not possible by MIM.
The outcome of this study was that these technologies claimed the ability to produce candidate parts and the resulting cost structures were feasible for low production numbers.
This current portion of the study will examine actual parts made by these various technologies and evaluate their abilities to achieve tolerances, surface finishes, and densities.
078-R - Quantification of Defects in Laser Powder Bed Fusion with Process Interruptions
Dana Drake, EOS of North America, Inc.
A failure during a component’s manufacture can often be correlated to distinct features observable during or after the manufacture or raw material processing (e.g. an impurity in an ingot, a forging crack, solidification porosity, or cracking during rolling). However, in additive manufacturing (AM), raw material feedstock undergoes melting, solidification and near net manufacture within the same process. AM processes can experience interruptions in the build process, or build pauses, due to any number of causes. Three identical builds endured three representative time intervals to simulate those pause length scales commonly encountered in Metal Laser Powder Bed Fusion (M-LPBF) and were compared to an identical, but unpaused build. Inconel 718 test coupons built on an EOS M290 Laser Powder Bed Fusion system were tested and characterized to provide insight into the effects of build pauses on the microstructure, porosity defects and changes in both local and bulk mechanical properties. There was a visible witness mark on the outer surface of all printed test coupons of all pause lengths that corresponded to the paused layer. While easily distinguishable on the surface, porosity near the paused region and the mechanical properties over that region evidenced little, if any change. The microstructural indications were subtle, but distinguishable in the etched condition. The witness mark stands out in contrast due to the built part below it that cooled, shrunk and over which powder was spread in a potentially thicker layer. However, despite this feature being easily discernable to the eye, and measurable in cross section, it did not appear distinctly in surface roughness measurements, nor in static mechanical testing (tensile and microhardness tests).
227 - Effects of Process Parameters on Surface Roughness of 316L SS Samples by Powder Bed Fusion
Steven M. Hoover, California Polytechnic State University
The purpose of this project is to investigate the scan strategy of selective laser melting (SLM) for evaluation of material mechanical properties and surface finish. Test samples were created that feature 0 to 90 degree angles in increments of 10 degrees, in order to study the influence of specific parameters.
151 - Coarse Tungsten Carbide Produced via Binder Jet 3D Printing
Ravi Enneti, Global Tungsten & Powders Corporation
Until recently, cemented carbide produced via binder jetting (BJ) resulted in microstructures with mixed WC grain size. Those materials exhibit excellent hardness and wear resistance but, have transverse rupture strength that is lower than the strength of cemented carbide with a uniform grain size. The present investigation details the development of a BJ coarse tungsten carbide (WC-12%Co) that displays a uniform sintered microstructure. The starting powder has excellent printability and can be sintered to full density using standard sintering practices (sintering temperature of 1435°C). The sintered microstructure with relatively uniform WC grain size and uniform Co distribution resulted in a substantial improvement in the transverse rupture strength. Other mechanical and wear properties are also presented. Parts over a wide range of sizes (from <1 g to 9 kg) and geometric complexities have been successfully printed and sintered with the new material.
054 - Small-Scale Mechanical Response of Cemented Carbides
Luis Llanes, Universitat Politècnica de Catalunya - BarcelonaTech
The unique combination of properties exhibited by cemented carbides (usually referred to as hardmetals) has made them preeminent material choices for extremely demanding applications. Although there exists extensive information on their mechanical behavior at the macroscopic level, knowledge on the small-scale response of these materials is rather scarce. This is particularly true regarding experimental data and analysis on the influence of phase nature, crystal orientation and interfacial adhesion strength on hardness, deformation and/or damage mechanisms. In this contribution, novel micromechanical testing approaches, as applied to cemented carbides, are presented. They include statistical analysis of large amount of nanoindentation data, compression of FIB-milled micropillars and fracture testing of notched microcantilevers. Information gathered provides an innovative view on the mechanical response of these materials at micro- and nanostructural length scales. Such knowledge becomes crucial not only to improve the performance of hardmetals but also to develop ceramic-metal composites beyond WC-Co systems.
181 - Reinforced Concrete Drilling with Cemented Tungsten Carbide Drill Bits: Wear and Fracture Mechanisms and Predictive Failure Analysis Based on Finite Element Modeling and Weibull Statistics
Steven Moseley, Hilti AG
Rotary-percussive drilling in steel reinforced concrete subjects cemented tungsten carbide drill bits not only to intensive wear but also high mechanical loading which may lead to premature failure due to overload or fatigue fracture.
In this work, finite element (FE) simulation methods based on transient (dynamic) impact loading and quasi-static indentation have been used to describe the thermomechanical load spectrum acting on the drill bits. These simulations estimated the stresses and temperatures generated which were then correlated with the experimental findings regarding crack initiation sites and regions experiencing thermo-mechanically induced surface microstructural modification.
Additional FE simulations have been performed to predict the influence of the local cemented carbide microstructure on the fatigue properties and Weibull statistics have also been employed to estimate failure probabilities based on measured mechanical properties.
Together, these complementary methods enable confident prediction of component reliability in this challenging application. This paper presents an in-depth case study.
Special Interest Program Abstracts
SIP 2-1 Alan Lawley Memorial Symposium I: Atomizing
547 - Atomization for PM: Past, Present and Future
John Dunkley, Atomizing Systems Ltd.
Metal Powder production first became a “hot topic” in the 1960s but scientific work fell away later. The advent of HIP, then MIM and, most recently AM processes has, in the last decade, lead to an exponential increase in development in the PM field in general, and special powder production in particular. Alan Lawley‘s 1992 book on atomisation was a comprehensive review which helps to illuminate the major milestones in 20th century atomisation. In addition we can review developments in the 21st century, and future prospects for the theory and practice of atomisation for PM.
561 - Approaching Lawley’s Vision: Tuning Close-Coupled Gas Atomization to Target Additive Manufacturing by Precision Powder Making
Iver Eric Anderson, FAPMI, Ames Laboratory
Springing from Alan Lawley's classic 1992 book, ATOMIZATION, The Production of Metal Powders, the quest for precise powder making sometimes has taken a winding path, much like one of his classic stories. However, with the ever-stronger pull of additive manufacturing (AM), metal powder manufacturers have a new sense of urgency to accurately generate each batch to fit a prescribed powder size distribution, particularly for unique alloy compositions produced for only one AM process. Powder quality also is driven to improve to satisfy the need for free flowing powder in coarse, fine, and (even) ultrafine size ranges and to eliminate sources of residual porosity in as-built parts. Using Lawley’s inspiration, our team of multi-phase flow modelers and atomization process experimentalists developed sufficient understanding of close-coupled gas atomization (CC-GA) to design improved gas die geometries and operating parameters, which will be reviewed. Supported by USDOE-EERE-AMO through Ames lab contract no. DE-AC02-07CH11358.
569 - Evolution of Gas Atomizing for Advanced Manufacturing Processes
Paul Davies, Sandvik Osprey Ltd
Among his many contributions to the world of Powder Metallurgy, Alan Lawley and his team at Drexel championed ground-breaking developments in Spray Forming: a technology invented by Osprey Metals in 1974. The production of rapidly solidified billets and tubes to achieve refined microstructures directly from the melt, spurred a multitude of research efforts leading to many commercial successes, some still in operation today. It is interesting to reflect on the evolution of this technology and to contrast with the ‘new wave’ of Additive Manufacturing technologies for the manufacture of complex near net shape products. This review will focus on atomising processes which underpin these manufacturing processes and that have been developed and optimized over decades to deliver increasingly nuanced products to meet the challenges of future manufacturing technologies.