PowderMet AMPM Special Interest
184 - Progress in Gas Atomization Reaction Synthesis of Powders for Advanced Consolidation of Oxide Dispersion Strengthened Ferritic Steels
Iver Anderson, FAPMI, Ames National Laboratory
To replace mechanical alloying that needs days of milling and suffers from contamination, and inhomogeneity, oxide dispersion strengthened (ODS) ferritic steels, e.g., “14YWT,” were made with powders from gas atomization reaction synthesis (GARS). The Fe-Cr alloys contained Y, W, Ti, and Zr and are atomized with Ar+O2 to produce Cr-enriched surface oxide. TEM analysis of GARS powders revealed that the surface oxide layer characteristics are controlled by oxygen concentration and size-dependent droplet cooling during rapid solidification. During solid state consolidation trapped powder surfaces become oxygen reservoirs that are released on heating above ~900C for reaction with Y-containing intermetallic compounds within each particle, forming highly stable oxide dispersoids. In this work, alloy composition and O2 levels were varied to produce desirable precursor powders for consolidation either by solid-state friction/stir shearing with indirect extrusion or by laser-powder bed fusion to enhance oxide dispersion strengthening. Support from USDOE-ARPA-E through Ames Lab contract DE-AC02-07CH11358.
015 - Automated Inert Expanding Gas Blanketing for Clean Powder Production
Jason McHood, Airgas, an Air Liquide Company
Inert expanding gas blanketing process has been applied to 180+ foundries around the US over the last couple decades as it elevated the philosophy of a clean metal melting process. Preventing the creation of metal oxides due to exposure to air rather than having to clean the oxides up in post processing. A recent installation of the process in a powdered metal production facility realized over a 60% reduction in slag/loss yield, a greater than 70% reduction in final powder total oxygen content (oxides and free oxygen), a 30% reduction in melt cycle time, and extended furnace lining life. The reduced oxygen in final powder nearly eliminated high cost scrapped heats due to off specification material. The main innovation in this new installation was that it was the first fully automated installation with flow controls, flow meters, PLC or DCS capable programming, as a process control optimization and overall safety measure. Being the first fully automated out of 180+ installations, this opens up numerous process improvements to the process. These melting parameters, testing results, control methods and process control improvements are reviewed as well as a summary of the benefits realized through this process application.
096 - Sustainability of Inert Gas Atomised Powders
Paul Davies, Sandvik Additive Manufacturing
Powder metallurgy is recognized as a green technology and the production of metal powders by inert gas atomization for advanced manufacturing technologies, including Additive Manufacturing (AM) & Metal Injection Moulding (MIM), can provide the key elements of a sustainable low impact production process. In this presentation, important sustainability strategies, initiatives and science-based targets will be presented, from metal powder producers' point of view. Sourcing and selection of raw materials, especially recycled metals, are discussed in light of the ambitious target of maintain 90% circularity. The mining & production of elemental materials, for the production of alloy powders, have varying levels if environmental impact, largely based on the refining processes. Many of which are energy intensive, generate high levels of waste, some-times toxic in nature and in many cases are regionalized to countries with challenging work practices. Prompting a detailed analysis of sustainability and carbon footprint, in terms of environment, human resource, supply chain management and ethical procurement, against ambitious targets over realistic time frames. Examples of replacement & substitution of elements with relatively high environmental impact, as well as high cost and potential health hazards, such as cobalt & nickel, are presented, including the development of new cobalt free maraging steels. New sustainability initiatives, including investment plans, regional stocking and e-commerce, are presented in order to maintain and support the long-term sustainability of Inert gas atomized powders.
PM-4-2 Testing PM Parts and Materials
951 - Leveraging Quantitative Fractography to Estimate Defect Severity from the X-Ray Computed Tomography of Additively Manufactured Titanium
Ian Wietecha-Reiman, Penn State University
Scatter of fatigue life in additively manufactured (AM) components continues to be a challenge in the design for fatigue of AM Ti-6Al-4V. This challenge may be overcome by incorporating quantitative fractography techniques to predict how processing defects, as imaged using x-ray computed tomography (XCT), impact fatigue life. Post-mortem analysis of fracture surfaces using scanning electron microscopy and confocal white light interferometry reveal important geometric relationships that can be used to model the fatigue crack growth and radius of curvature of processing defects. Metrics derived from these relationships are then assessed using survival analysis statistics which both rank processing defects based on relative severity and provide estimates of fatigue life. Actual specimen fatigue lives correlated well to the knee bend of the survival analysis curves and were used to establish confidence intervals for expected fatigue life.
176 - Leveraging Automated Optical Microscopy to Conduct Degree of Sinter and Localized Density Mapping across Whole PM Part Cross-Section
Xin Yin, Burgess-Norton Mfg. Co.
Powder metal components have density variation throughout their cross section, the variation can be reduced through tooling geometry optimization and manufacturing techniques. Since density is related to the mechanical properties of powder metal components, understanding localized density variation has a tangible impact on productivity and profitability of part manufacturers. Traditionally the density of PM parts was measured through Archimedean methods. However, the measurement is limited by the number and size of the sample sections. In this study we use automated metallographic microscope to improve the density measurement resolution down to sub-1-mm2 segments. Additionally, we will show the correlation between the optically derived theoretical density and Archimedean density measurements. Pore roundness was a metric used in literature to measure “degree of sinter”. In this study we will use automated image analysis to impart statistical significance to the morphology of sample porosities, and to experimentally decide the best sintering time for common PM alloys.
915 - Effect of Die Filling Density of Pharmaceutical Powders on Phase Transformation During Tablet Compaction
Phuong Bui, Drexel University
During tablet compaction, initial crystalline of active pharmaceutical ingredients (API) may transform into another crystalline or amorphous state depending on the local stresses. Over the past years, compression induced phase transformations have attracted attention, but there are difficulties in establishing a conceptual framework for understanding and controlling this problem. Prior studies on the polymorphic conversion in tablets typically reported the percent of transformation as a function of applied compaction pressure. However, geometrical characteristics and stress history of the compacted material can also potentially influence these polymorphic conversions. Our goal is to understand the relationship between the efficiency in die filling density to local variation of the stresses and in turn their effects on the transformations using Chlorpropamide as a model API. The long term of this work is to develop a constitutive model that can optimize the design and processing conditions of materials with potential transformation behaviors during tableting.
AM-4-1 Applications: Automotive, Heat Exchanger, Power
163 - Metal Binder Jetting of Automotive Components
Mattia Forgiarini, Azoth
Metal Binder Jetting (MBJ) is a promising Additive Manufacturing (AM) technique as it can be used to form complex geometries out of almost any type of powder without the use of heat input at high production rates and low manufacturing cost. In this work MBJ printing is explored as a fabrication process for an impeller composed of a Ni-base superalloy for a turbocharger application. Conventional wrought and machining methods used to manufacture impellers to-date offer good mechanical properties for end-application performance however the high material “buy-to-fly” ratio has drawn interest to explore AM approaches. Fusion-based AM technologies, such as laser and electron beam powder bed fusion, are limited with deposition rates and are challenged to print high gamma prime/gamma double prime strengthened Ni-base alloys due to their poor weldability. For these reasons, the development of 3D printing and post-processing approaches using fusionless MBJ for Mar M 247 was investigated. Conventional post-process Hot Isostatic Pressing (HIP) and heat treatment was applied to establish baseline microstructural and mechanical property data along with the evaluation of an over-speed impeller spin test. Results were then leveraged to establish process-structural-property relationships for further optimization of the microstructure through post-process combined HIP and heat treatment to maximize part performance.
011 - Development of Novel Alloys and AM/PM Manufacturing Methods for Fabrication of Extreme Environment Heat Exchangers
Austin Mann, Boeing
Boeing Research & Technology is developing topologically optimized heat exchangers, advanced alloys, and manufacturing processes for use in long-life supercritical CO2 (s-CO2) Brayton power cycles, which can be employed in terrestrial power generation and in high efficiency integrated power & thermal management systems for high speed aircraft. These applications require metallic materials solutions capable of continuous operation at temperatures up to 1000°C and pressures above 80 bar for tens of thousands of hours in s-CO2. Novel extreme environment nickel-based superalloys and refractory complex concentrated alloys have been developed for this rigorous application, and fabricated into heat exchangers via additive manufacturing and powder metallurgy processes. Mechanical, thermo-physical, and environmental properties of the novel alloy systems will be discussed, including simultaneous evaluation of high temperature corrosion (oxidation), creep, and environmentally assisted cracking of metallic materials in s-CO2 in a uniquely designed simulated service test bed.
110 - Fabrication of High Temperature Parts Composed of Titanium-Zirconium-Molybdenum Alloy (TZM) Using Powder Bed Fusion (PBF)
Michael Brand, Los Alamos National Laboratory
High temperature structural materials are in great demand for power, chemical and nuclear industries which can perform beyond 1000oC as super alloys usually fail. Mo based TZM (Titanium-Zirconium-Molybdenum) alloy is capable of retaining strength up to 1500oC with excellent corrosion compatibility against molten alkali metals. Currently this alloy is considered an important candidate material for high temperature compact nuclear and fusion reactors. Due to the reactive nature of Mo and having a high melting point manufacturing this alloy by conventional process in unsuitable. Using the EOS M290 complex shapes using complex materials can be fabricated by using the Powder Bed Fusion (PBF) process. Using PBF, ideal parameters for TZM alloy will be developed. Tensile bars and small replica reactor parts will be fabricated. Mechanical properties obtained from parts fabricated by the conventional process will be compared to the mechanical properties of the additive manufactured parts.
AM-4-2 AM Feedstock Characterization I
052 - Method for Evaluating the Effect of Elevated Temperatures on the Flow Properties of AM Feedstock Powders
Amalia Thomas, Freeman Technology
Additive manufacturing, and powder bed fusion in particular, often involves heating as part of the production process. Thermal management of the build chamber is known to affect part quality by mitigating distortion and residual stresses caused by heat differentials during sintering or melting. However, an increase in ambient temperature can affect powder processability in multiple ways: solid particles may deform or partially melt, moisture may evaporate, and the density of the entrained air can decrease significantly. Heating may have a conflicting effect on the powder recoating operation, negatively affecting the average layer thickness or density uniformity, which can in turn lead to different defects in the finished part. The combined effect on powder flow properties of all the factors that are affected by a change in temperature is very complex to model and predict from particle characteristics.
We present a testing procedure to measure directly the effect of temperature on the powder flow properties measured with an FT4 Powder Rheometer® (Freeman Technology, UK). In the proposed setup powders can be heated to temperatures up to 200°C and the temperature and flow properties of the powder can be monitored in real time, as a function of temperature. We investigate the changes in flow properties during both heating and cooling processes for a variety of powder samples. We show that heat can affect powder flow properties in very distinct ways and at different speeds of heating, and we are able to interpret results to differentiate the effects of moisture loss and particle softening.
109 - Assessing the Impact of Moisture on AM Powder Flowability
Louis-Philippe Lefebvre, National Research Council Canada
Recent studies have shown that the exposure to moisture may affect powder properties. Small amount of moisture on the surface may affect the behaviour of the powders and impact additive manufacturing (AM) process stability, reliability and productivity as well as component microstructure, composition and properties. This paper presents the effect of moisture adsorption of the properties of different AM powder feedstocks. The impact of moisture adsorption on different flowability indexes is presented and discussed. The results indicated that the amount of water adsorbed and the impact of the water adsorption depends on the powders and the flowability test methods and indexes do not have the same sensitivity to moisture.
144 - A Review of Rotating Drum Rheometer Measurements Used to Characterize Powders for AM Applications
Greg Martiska, Mercury Scientific Inc.
Rotating drum rheometers are widely used in the powder AM field to characterize powders. However, the measurements made by these devices are not well understood. This paper will review the various measurements made by rotating drum rheometers and how these measurements can be used to characterize powders for AM applications.
AM-4-3 Thermal Post Processing
140 - L-PBF F357 Aluminum Alloy: Heat Treatments and Thermal Aging
Edel Arrieta, University of Texas at El Paso
In the aerospace industry, numerous critical legacy parts were traditionally fabricated with casted F357 aluminum alloy. The alloy has also been proven suitable for fabrication and qualified using Laser Powder Bed Fusion Additive Manufacturing (L-PBF AM), by leading material and system manufacturers. In addition to material data sheets from manufacturers, there are some research articles reporting the mechanical performance of L-PBF F357 but samples are of few specimens. This work, with data from 540 specimens, not only addresses the lack of publicly available data but also presents the mechanical properties of L-PBF F357 subjected to different heat treatments. Moreover, the aging effects of temperature and time on the heat-treated L-PBF F357 samples are presented. The thermal aging study consisted of two different groups of F357 samples under two different temperatures each; one at 285°F and the other at 350°F, with exposure times up to 1000 hours continuously. The temperatures were selected based on the expected service temperatures of current aerospace components made of F357 alloy. This work reports the evolving effects of the aging temperature and the exposure time on mechanical properties such as yield and ultimate tensile strengths, and elongations. Additionally, micrographs showing the microstructural changes due to heat treatments and aging are presented. The work finalizes with discussion and concluding remarks on the correspondent differences and relationships observed between mechanical performance, microstructural and fractographic evidence.
201 - Hollow-Strut Metal Lattice Materials: A Viable Alternative to Solid-Strut Lattice Materials
Ma Qian, Royal Melbourne Institute of Technology
Intricate hollow-strut metal lattice materials are an emerging class of novel metallic cellular materials enabled by powder bed fusion (PBF) additive manufacturing (AM). However, their manufacturability by laser powder bed fusion (LPBF) is not established yet. This first part of this work investigates the LPBF manufacturability of Ti-6Al-4V hollow-walled struts with respect to strut outer diameter, wall thickness (regulated by laser scan path) and inclination angle, at the typical lattice unit length of 10-15 mm. The manufacturability is reliable for outer diameters exceeding 0.5 mm and wall thicknesses exceeding 0.24 mm over the inclines of 22.5°-90°. To ensure a manufacturable hollow cylindrical channel by LPBF, we recommend a minimum inner diameter of 4Dv(90), where Dv(90) is the powder size below which 90vol.% of the powder is included. The second part evaluates the mechanical properties of the hollow-strut Ti-6Al-4V lattice materials printed by LPBF. Under uniaxial compression conditions, they are consistently stronger and stiffer (up to 60% better) than their solid-strut counterparts of the same relative density by both experiments and finite element analysis (FEA). The underlying reasons are elucidated using analytical models derived from the Timoshenko-beam theory, which considers deformation by concurrent stretching, bending and shear, rather than the single-mode deformation mechanism assumed by the Gibson-Ashby model. We conclude that hollow-strut metal lattices offer a unique option for lightweight designs, with better mechanical properties at the same or even lower density than their solid-strut metal lattice counterparts.
924 - Tensile Deformation Behavior of Additively Manufactured IN625 at Different Temperatures: LPBF vs. LP-DED
Arun Poudel, Auburn University
This study compares the tensile deformation behavior of laser powder bed fused (L-PBF) and laser powder direct energy deposited (LP-DED) Inconel 625 (IN625) at -195 °C, 20 °C, 200 °C, 425 °C, and 650 °C. The heat treatment involving stress relieving, hot-isostatic pressing, and solution treatment resulted in equiaxed grains accompanied by annealing twins. Tensile results showed decreasing strength with increasing test temperature in L-PBF and LP-DED which was attributed to the decline of the deformation twin density in the material. However, the tensile strength of LP-DED was lower than L-PBF ascribed to its larger grain size, i.e., nearly three times. The ductility of L-PBF and LP-DED IN625 was observed to be stable from -195 °C to 425 °C; however, a sudden decrease was observed at 650 °C. In LP-DED specimens, the tensile fracture was governed by the decohesion of carbides, whereas it was carbides and Al2O3 in L-PBF specimens.
029 - A Novel, Low Cost, Highly Alloyed Cast Iron Powder for the Production of High Performance Binder Jet Components
Olivier Sioui-Latulippe, École Polytechnique de Montréal
A new low cost, highly alloyed cast iron (designated MC15-5) has been developed, exhibiting beneficial features and characteristics for industrialization and use in high temperature or wear resistant applications. This alloy combines technical performance and commercial value, exhibiting desirable microstructure, near theoretical density, high hot hardness, and exceptional wear resistance in Binder Jet-produced samples. The unique combination and levels of Cr, Mn, and C (nominally 15, 15, and 5 wt%, respectively) eliminate or reduce the need for expensive alloying elements such as Mo, W, and V.
Binder Jet fabrication of MC15-5 test samples is described, and the specific metallurgical and performance aspects characterized and measured. The ease of achieving >99% theoretical density using relatively wide and coarse powder size distribution (PSD of 45 to 106 μm) indicates high sinterability, due to the presence of a liquid phase. The phase diagram for the composition is calculated using thermodynamic modeling software, and the powder characteristics, microstructure, density, macrohardness, microhardness, hot hardness, and wear resistance is measured and characterized. Of particular interest is the complex multi-phase microstructure and its transformation during post-sinter thermal treatment and quench.
093 - On the Use of Boron to Promote the Densification of AISI D2 Tool Steel Components Produced by Binder Jetting
Simon Gelinas, Laval University
Compared to laser/electron beam melting additive manufacturing (AM) processes, binder jetting (BJ) is better suited for the fabrication of parts made of high-carbon tool steels. In BJ, part densification is achieved through sintering. The latter normally involves much slower cooling rates than those measured with other AM powder bed technologies that are particularly susceptible to cracking when manufacturing highly hardenable steel grades. Significant densification through solid-state sintering normally requires resorting to very high temperatures and longer periods of time. An alternative strategy to increase densification is to use the liquid phase sintering approach. This work investigated the effect of small additions of pre-alloyed boron made to a water atomized AISI D2 steel powder on its densification during sintering. The results confirmed that pre-alloyed boron considerably increases the densification of such parts, even if "conventional" sintering conditions, i.e. 30 minutes at 1200 ˚C, were used.
139 - Metal Binder Jetting of Cobalt Chrome Molybdenum ASTM F75
Lorenzo Marchetti, Digital Metal
Cobalt chrome alloys are widely used for biomedical and dental implants thanks to their good mechanical properties, wear resistance and excellent corrosion resistance. Today these parts are either cast in custom-made molds, injection molded or manufactured with electron beam or laser powder bed fusion technologies. A limiting factor in casting and MIM is the production of molds, while in EBM and LPBF the need for support structures, degradation of recovered powder and lower overall productivity.
The adoption of Metal binder jetting (MBJ) technology for the production of components in cobalt chrome can simplify the manufacturing of customized medical implants, enabling freedom of design, typical of additive manufacturing, and high productivity. In MBJ parts are printed at ambient temperature, preserving the recovered powder quality. Densification takes place in a sintering step, where the absence of melting helps preserve the fine features of the parts. The resulting physical and mechanical properties of parts printed and sintered in CoCrMo grade F75 are here reported.
Special Interest Program Abstracts
SIP 2-2 Tungsten II: AM of Refractory Metals
504 - Effects of Process Parameters in Laser-Powder Bed Fusion of Tungsten
Sundar Atre, University of Louisville
Tungsten components are increasingly being used at ambient and elevated temperatures in energy storage and nuclear applications. The conventional powder metallurgy-based production of tungsten components has limitations on realising complex shapes due to the requirement of part specific tooling and extreme processing conditions. Use of laser powder bed fusion (LPBF) additive manufacturing as an alternative to conventional manufacturing techniques, as this process can significantly improve the design flexibility and thereby in-service performance. However, to realise a component in LPBF requires a thorough understanding of the role of process parameters on the defects and microstructural evolution. In this study, by varying process parameters and using an ANOVA analysis, it was found out that the layer thickness is a critical process parameter to achieve full melting and to produce defects-free high-density components. Efforts are also made to understand the role of layer thicknesses (10µm, 20µm and 30µm) in surface roughness, microstructural evolution, and mechanical properties. The results of this study will be presented in this work.
505 - High Temperature Mechanical Properties of Additively Manufactured Nb-C103 Alloy with Environmental Barrier Coating
Tyler DuMez, H.C. Starck Solutions
Nb-C103 is a niobium-based refractory alloy for high temperature applications, however high operating temperatures can cause oxidation affecting physical and mechanical properties. This paper evaluates the effects of a silicide environmental barrier coating (EBC) at high temperatures under atmospheric conditions on the properties of Laser Powder Bed Fusion (L-PBF) printed parts. Subscale specimens were printed and tested in coated and uncoated conditions at both room and elevated temperatures. These results were compared to uncoated specimens tested under inert conditions.
506 - Dimensional Capability of WHA Components Consolidated by Binder Jetting Additive Manufacturing
Salvator Nigarura, Global Tungsten & Powders Corporation
Binder jetting 3D printing (BJ3DP) is an emerging technology that can enable the production of tungsten heavy alloy (WHA) parts of great geometric complexity. Despite its promise, the industrial use of this technology has been hindered by the dimensional variation and associated distortions that take place during sintering. Compared to die pressed components, BJ3DP parts have lower densities in the as-printed condition. Liquid phase sintering of low green density and complex geometry parts leads to nonuniform densification and shape distortions in the final part.
In this study we present BJ3DP parts produced using a specially developed WHA powder and compare the dimensional variation of BJ3DP parts against the variation of parts pressed in dies.
The results confirm that tight dimensional control of BJ3DP WHA parts can be achieved through the use of special purpose sintering fixtures and the optimization of the thermal profile during sintering.