PowderMet AMPM Tungsten Special Interest
SESSION P01 Modeling to Enable Novel Powder Synthesis
183 - Thermo-Fluid Analysis of Satellite Formation During Close-Coupled Gas-Atomization for Production of Precision Metal Powders
Jordan Tiarks, Ames Laboratory
Formation of “satellite” attachments on pre-alloyed powder produced via close-coupled gas atomization (CC-GA) presents a significant technical challenge for additive manufacturing (AM) to reach its full potential for critical energy applications. Inconsistent feedstock packing densities and irregular layer spreading due to poor powder flowability result in unpredictable build quality and performance. Through advancements in understanding the thermal profile evolution and state of solidification of these powders throughout the atomization spray, new processing methods can be developed to reduce the probability of particle-to-particle collisions which result in satellite attachments. Implementation of spray chamber modeling and experimental investigations have led to the development of several approaches for satellite suppression, including supplemental gas flows and passive baffle devices. Funnel-flow and powder rheometry methods combined with micrographic imaging reveal the utility of these approaches. Progress on satellite mitigation strategies deployed at Ames Laboratory will be reported. Supported by USDOE-EERE-AMO through Ames lab contract DE-AC02-07CH11358.
184 - Gas-Die Geometric Requirements for Producing Uniform Flows in Close-Coupled Gas Atomization: A Numerical Study
Franz Hernandez, Ames Laboratory
Gas-die manifolds are reservoirs of high-pressure gas that generate the high-speed flows needed for atomization. Uneven distribution of pressure in the manifold can lead to non-axisymmetric gas flows, exiting either discrete jets or annular slits, and cause swirling, unbalanced melt behavior, freeze-off and splatting. The gas-die geometry can be described by the following parameters: the number of inlets, the respective offset distance and incident angle; the inlet critical area; the manifold diameters or shape; and the manifold height. Here, the effects of manifold diameter ratio, critical area and normalized offset are studied numerically in 3D for different inlet diameters and number of inlets. A compressible viscous-fluid flow solver considering argon gas is employed and results discussed. When the critical area is relatively smaller than the inlet area, lower Mach numbers and improved pressure distribution are expected. Work supported by USDOE-EERE-AMO and USDOE-OE through Ames Laboratory Contract No. DE-AC02-07CH11358.
180 - Close-Coupled Transferred Arc Plasma-Wire Atomization
Joseph Tunick Strauss, FAPMI, HJE Company, Inc.
Plasma-wire atomization is commercially practiced by several concerns. The current technology utilizes several non-transferred arc plasma torches focused on a wire, where it is melted by the heat and atomized by the action of the plasma gas. Although this method is versatile and has the ability to atomize reactive and refractory alloys, the specific energy and gas consumption are most likely high.
This paper introduces a transferred arc plasma wire atomization technology with the potential to overcome some of the inefficiencies of conventional non-transferred arc plasma atomization systems. The preliminary design and operational trials will be presented in this paper.
SESSION P02 Process Optimization and Productivity Improvement I
211 - Modeling of the Grinding Process of Thermal Barrier Coating Using the Smoothed Particle Hydrodynamics Method
Jian Zhang, Indiana University - Purdue University Indianapolis
Damaged thermal barrier coating (TBC) can be removed through a grinding process. In this work, the process is simulated using the orthogonal cutting model by the smoothed particle hydrodynamics (SPH) method. The model is built on a simulated microstructure of electron beam – physical vapor deposition (EB-PVD) fabricated coating. Four factors, including tool geometry, rake angle, cutting depth, and cutting speed, are investigated. The results show that the cutting tool with a blunt edge causes higher effective stress, reaction force, and coating temperature, compared to a sharp tool. The surface roughness with a sharp cutting tool edge radius is low. The horizontal reaction force decreases with the increasing rake angle. In addition, the horizontal cutting force increases with the increasing cutting depth. The results are consistent with the analytical solutions based on fracture mechanics. Furthermore, the larger cutting speed causes a higher horizontal cutting force and coating temperature.
126 - A Comparison of a Novel Approach to Delubrication and Sintering to the Conventional Sintering of Advanced High Density Lubricant Containing Compacts
Jacob Feldbauer, The Pennsylvania State University—DuBois
As the need for higher density compaction increases, new advanced lubricants for high density compaction have gained in popularity. In this work, a newly developed delubrication and sintering process is compared to conventional processing of compacts containing various amounts of lubricant and the impact of compact density on physical properties, production rates, and quality. This approach provides other opportunities to optimize and improve the sintering process in total.
127 -Comparison of a Novel Approach to Delubrication and Sintering Process to the Conventional Sintering of EBS Containing Compacts
Scot Coble, The Pennsylvania State University—DuBois
Ethylene bis-stearamide wax (EBS) is the is the work horse of lubricants used in the powder metal industry. However, the removal of this lubricant has been a difficult task and negatively impacted the industry for a very long time. In this work, a new delubrication and sintering process is compared to conventional processing of compacts containing various amounts of EBS and the impact of compact density on physical properties, production rates, and quality.
The new process is a paradigm shift in the way powder metal products are sintered. Although this process focusses on the complete removal of lubricants from the compact, the approach provides other opportunities to optimize and improve the sintering process in total.
SESSION P03 Machine Enhancement for Productivity and Optimization
086 - Enhancing the Machining Consistency of PM Components—A Look at a New Machining Additive
Neal Kraus, Hoeganaes Corporation
Powder Metallurgy part machinability is an inherently challenging yet critical process. While net shape in nature, PM parts show significant differences when being machined in comparison to wrought products. Porosity and thermal differences along with non-homogenous microstructures are just some of the reasons why PM machining is often characterized as difficult. Machinability enhancers like MnS have been the backbone of the industry response to these challenges but proves to cause secondary issues when processing; namely enhanced corrosion. As such, in this paper and in response to these issues a new additive with a focus on the drilling operation has been studied.
032 - 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
075 - New Machining Enhancer for High Strength Powder-Forged Connecting Rods
Bo Hu, North American Höganäs Co.
Powder-forged connecting rods for automotive applications require significant machining with multiple operations to provide precise dimensions and surface finish. Powder-forged connecting rods are commonly manufactured from copper steels with a conventional machining additive such as MnS. Recent developments in advanced machining enhancers show potential in replacing MnS used in various as-sintered steels. In this study, laboratory tests with powder-forged pucks and actual connecting rods were conducted to evaluate the performance of advanced machining enhancers in improving the machining of high strength powder-forged materials. Results obtained from machining tests and mechanical tests indicate that the advanced machining enhancers have potential in improving the machining of powder-forged materials and achieving higher productivity. The conclusion of the feasibility assessment in this study was to proceed with mass-production machining trials in order to validate the performance of the new machining additive.
SESSION A01 Design for AM
035 - AM-Enabled Design Enhancement of an Aeroderivative Gas Turbine Combustion Transition Duct
Zachary Dyer, Siemens Power Generation, Inc.
The subject of this presentation is an SGT-A05 combustion transition duct, in which effusion cooling is minimized by the use of a dual-wall construction with an internal lattice structure. This concept minimizes the need to inject cooling air into the hot gas path by passing air over a thin inner shell supported by a lattice structure. The lattice design was taken from sub-component testing, and optimized for flow considerations as well as structural ones. Numerous other design-for-additive techniques and principles were employed resulting in minimization of non-functional supports as well as multi-part combination which eliminates the need for assembly welding of transition-to-vane fixing devices. The goal of this paper is to demonstrate the development of such a transition (in terms of calculations and laboratory testing).
205 - Designed Internal Porosity to Improve the Fracture Toughness of Additively Manufactured Parts
Kaitlynn Conway, Clemson University
With the introduction of additive manufacturing (AM), AM technologies have opened the ability to have diverse topologies of metamaterials. Several metamaterial mechanical properties such as stiffness and toughness however, scale with density, limiting the engineering applications where metamaterials could be used. In this study, planes of weakness were added to 316L gyroid surface metamaterials to divert propagating cracks to grow in less damaging directions. This increased the toughness of the lattice material, enhancing possible uses of the metamaterial. The resulting AM gyroid metamaterial possessed a fracture toughness that outperformed that predicted by Gibson and Ashby for low-density material by an order of magnitude. Improving the mechanical properties of AM metamaterials increases their functionality in lightweight structural applications.
190 - Additive Manufacturing of Refractory Grid Structures—Historical Overview
Juha Kotila, EOS Finland - Electro Optical Systems Finland Oy
The developments on laser beam properties of additive manufacturing equipment have enabled reaching higher and higher laser beam intensity levels. These high beam intensities have made possible to process materials with very high melting temperatures, e.g. refractory metals. Most of these materials are difficult or impossible process in conventional manufacturing methods to include thin walled sections, internal cavities or structures with significant weight savings.
SESSION A02 Laser Powder Bed Fusion Process
014 - Research of Specific Heat Treatment for AlSi7Mg0.6 Alloy Made by Laser Beam Melting
Cassiopée Galy, IRT Sait Exupéry
Aluminum alloys are strong candidates to develop Laser Beam Melting (LBM) process. Its low density, combined with design optimization made possible by additive manufacturing, provides the opportunity to reduce structure weight, which is a central development axis for the aerospace industries. In order to obtain desired materials properties, heat treatments are used commonly on cast AlSi7Mg0.6 alloy. However, due to specific microstructure formed during LBM, new heat treatments needs to be developed. This study aims the development of new heat treatments that allows an improvement of properties of AlSi7Mg0.6 parts made by LBM. Several aspects are studied to comprehend the relationship between mechanical properties and microstructure. For thus, several kinds of analysis have been performed. For instance, Electron Backscatter Diffraction Analysis (EBSD) has been correlated to mechanical tests to characterize material isotropy after heat treatment. Also, Differential scanning calorimetry (DSC) analysis has been completed with Transmission electron microscopy (TEM) observations to understand phenomena that occurred during the hardening process.
213 - Identification of the Nanoparticles Dispersion Mechanism in Hybrid Process of Ink Jetting and Laser Powder Bed Fusion
Milad Ghayoor, Oregon State University
Oxide dispersion strengthened (ODS) alloys are metal-matrix composites in which nano-scale oxides suppress grain boundary mobility at elevated temperature and enhance creep resistance. The laser powder bed fusion (LPBF) process was utilized to disperse nanoparticles of Al2O3 into the 316L stainless steel matrix. This study investigates the microstructure of 316L ODS alloy developed via two different additive approaches. First, 316L SS powder and alumina particles were mixed and used as feedstock for producing 316L ODS alloy. Second, ink-jetting in the LPBF process was utilized to manufacture 316L ODS. The ink, containing nanoparticles of Al2O3, was selectively deposited into the 316L powder bed, and then laser consolidated metal powder and nanoparticles into nanocomposite. Detailed microstructure characterization revealed that the Al2O3 were melted, precipitated, and homogenously dispersed in the matrix during solidification. As a result, ball-milling and hot consolidation and further machining are no longer required in additive manufacturing of ODS alloys.
004 - Directed Energy Deposition: The Triathlete
Michael Juhasz, FormAlloy
Directed Energy Deposition (DED) is a diverse additive technology excelling in 3 areas of metal Additive Manufacturing: Form, Enhance, Repair. With the powder-fed laser process, DED can FORM complex high-value components in a single-step method, ENHANCE part properties with additional features or multi-materials, and REPAIR parts with defects to reduce scrap. Directed Energy Deposition (DED), also referred to as Laser Metal Deposition (LMD) or Direct Metal Deposition (DMD), is an innovative Additive Manufacturing process which utilizes a focused laser to create metallic parts to near-net shape without the need for a bed of powder. This DED process deposits metal with a co-axially aligned laser/powder nozzle enabling complex geometries without the need for support structures, reducing machining time and nearly eliminating material waste. 3D printing parts with the LMD process can provide design features that can’t be achieved with conventional manufacturing methods, such as internal cooling channels and multi-metal parts.
SESSION A03 AM Powder Characteristics I
137 - Evaluating the Changing Sensitivity of AM Powders to Segregation and Humidity as They are Used and Recycled
Gregory Martiska, Mercury Scientific Inc.
Powders can change their flow properties as they are handled and used. They also can become more sensitive to segregation on handling and environmental conditions. This means that a powder that has been used or recycled may change its behavior due to handling and environmental exposure more than virgin material. This behavior is evaluated by testing the flow properties of virgin and used AM powders with rotating drum analyzer before and after exposure to segregation pressure and different environmental conditions.
214 - Effect of Powder Composition on Aging and Mechanical Response of Additively Manufactured 17-4 PH Stainless Steel
Derek Shaffer,The Pennsylvania State University—DuBois
The atomization gas used to produce 17-4 Precipitation Hardened (PH) stainless steel powder feedstocks has been shown to result in large variations in the as-deposited composition and microstructure. Specifically, compositional changes lead to differences in retained austenite fractions in as-deposited and heat-treated material. To evaluate the impact of these varying compositions and microstructures on material properties, samples made from nitrogen and argon atomized powder were created. After a series of tests, material made with argon atomized powder was found to have no austenite, resulting in mechanical and aging responses like the wrought condition. Material made with nitrogen atomized powder had increases in retained austenite and exhibited strain induced phase transformations. Furthermore, material made with nitrogen atomized powder in the as-deposited condition showed higher tensile strength while strain induced phase transformations also caused high ductility and discontinuous yielding. Material made with nitrogen atomized powder also had improved properties in aged conditions.
194 - Characterization of Plasma Spheroidized and Powder Bed Fusion Processed Commercially Pure Niobium
J. Scott O'Dell, Plasma Processes, LLC
Accelerators are necessary for the fundamental study of matter and its origins. A critical component of accelerators are the niobium superconducting radio frequency (SRF) cavities, which are used to accelerate the particles. Because of the significant number of niobium SRF cavities required for each accelerator, innovative manufacturing techniques are needed to reduce fabrication costs and to ensure high quality cavities are produced. Recently, 3D Additive Manufacturing (AM) methods have been shown to reduce the cost and fabrication time of complex components using conventional metals. However, the high melting temperatures, sensitivity to interstitial impurities, and difficulty of obtaining suitable feedstock materials have limited the 3D printing of refractory metals. Recently, innovative Plasma Alloying and Spheroidization (PAS) techniques have been developed, which enable the production of high purity, spherical refractory metal powders. During this effort, the PAS processing of commercially pure hydride/dehydride (HDH) niobium was evaluated for producing suitable feedstock for subsequent 3D printing of accelerator components. Preliminary results have shown the ability to produce spherical niobium powder with significant improvement in flowability, and metallic impurity levels similar to wrought superconducting grade niobium, i.e., Residual Resistivity Ratio>300 (RRR300). In addition, interstitial impurity levels were reduced to levels below commercially available high purity niobium powder after post-PAS processing. Using the PAS niobium powder, Electron Beam – Powder Bed Fusion (EB-PBF) processing methods were used to produce 3D printed niobium samples for preliminary characterization. Tensile testing of AM produced samples from PAS niobium showed the mechanical properties were equivalent or superior to wrought niobium. Preliminary RRR testing showed AM samples produced with commercially pure, PAS niobium powder had values equivalent to AM samples previously produced with nuclear reactor grade niobium feedstock.
SESSION T01 Tungsten Heavy Alloys I
069 - Review of Tungsten Heavy Alloys—Composition, Processing, Microstructure, Properties (Randall M. German,
Randall M. German, FAPMI, German Materials Technology
In spite of much effort over 90 years, liquid phase sintered tungsten heavy alloys converge to a few compositions and considerable similarity in phase relations, microstructure, and properties. Essentially these alloys converge to a natural trajectory during processing. As a consequence, standardized distributions functions describe the microstructure. The processing schedules aimed at high mechanical properties involve adjustments for impurity removal, segregation prevention, deformation, aging, and important dislocation mobility adjustments. Under the optimized cycles we find a broad range of mechanical property options.
084 - Investigations on Laser Powder Bed Fusion of Tungsten Alloys
Nabil Gdoura, Bayerische Metallerke GmbH
Laser powder bed fusion (L-PBF) offers significant potentialities for the design of complex part geometries. Due to the specific combination of properties, tungsten and tungsten heavy alloys are used for special applications such as X-ray and g-radiation shielding, balancing weights, collimators and molds, where complex geometries can be required for optimum performance. L-PBF of tungsten alloys such as W-Ni-Fe is challenging due to the high thermal conductivity, high viscosity of the liquid phase, the high melting point and sensitivity to thermal cracking. The effect of L-PBF processing parameters on the material microstructure of tungsten alloys has therefore been studied for different powder compositions, applying substrate pre-heating temperatures up to 800°C. Furthermore, the impact of thermal post-treatment has been investigated, leading to a microstructure close to conventionally sintered material. Fully crack-free samples have been generated from all powders, but residual pores can still be detected.
105 - Investigation of Laser Powder Bed Fusion of Tungsten Heavy Alloys
Michael Pires, Lehigh University
Selective laser melting of W-Ni-Fe tungsten heavy alloys (WHA) were investigated. The research objective was to establish a relationship between thermal history and the resulting microstructure obtained using a Renishaw AM400 unit. An incorporated reduced build volume (RBV) attachment was used to print 5 x 5 x 5 mm3 solid samples for two different WHA powders of varying compositions. Laser power, scan speed, point distance, hatch spacing, and layer height were varied to determine parameter optimization. Samples in excess of 99% “optical density” were achieved, with hardness values 200% greater than found in literature. The microstructures of these samples were examined via LOM, SEM, and EDS. It was determined that a powder layer height of 20 µm, point distance of >70 µm, exposure time of >100 µs, and laser power within 120-160 W resulted in greater sample density, resulting in reduced crack and pore formation.
Special Interest Program Abstracts
SIP 1-1 Improvement in Precision / Accuracy / Variation Control I: Material Improvements
548 - Material Options for Improved Dimensional Consistency
Roland Warzel, III, North American Höganäs Co.
Powder Metallurgy (PM) enables the manufacturing of high-volume components with near net shape capability. The required tolerances on PM components continues to tighten at the same time as the complexity increases. To minimize secondary machining steps, highly repeatable dimensional consistency is required. The dimensional consistency can be influenced by several factors with the material composition playing a large role in the tolerances which can be achieved. In this presentation, factors which influence dimensional consistency will be reviewed. Solutions which allow for increased precision will be presented.
559 - Use of Advanced Premix Solutions to Increase Dimensional Consistency
Julie Campbell Tremblay, PMT, Rio Tinto Metal Powders
The use of copper, nickel and molybdenum is widespread in the powder metallurgy industry. While molybdenum is generally prealloyed given its limited impact on compressibility, copper and nickel are very often admixed. The use of fine admixed additives can lead to segregation during packaging and transport and result in part-to-part variations that affect dimensional stability. Various solutions were developed to minimize segregation and improve part-to-part stability. Advanced premix solutions like organic bonding, diffusion bonding and conditioning improve resistance to segregation with the intention of improving part-to-part stability and therefore obtain better dimensional control. Examples will be discussed.
568 - Understanding the Factors Influencing PM Dimensional Change to Improve Part Consistency
Neal Kraus, Hoeganaes Corporation
One of the most desirable attributes of PM processing is the near net-shape that is possible with compacted parts. To optimize this technology, one must understand the factors that affect dimensional change through sintering in order to minimize the amount of additional processing (sizing, machining) that must be applied. This work aims to show basic factors that influence dimensional change in the most common PM alloys and offers possible solutions to improve both part-to-part and lot-to-lot consistency. Alternative alloys, advanced powder solutions, and enhanced processing options are applied in a production setting to reduce the need for secondary processing steps.