PowderMet          AMPM          Special Interest

032 - Characterization of Phase Transformation in Sinter Hardened Steels
Amber Tims, PMT, North American Höganäs Co.

Sinter-hardening is a thermal process in which a ferrous product (material) is sintered and then cooled at a rate sufficient to produce a predominately martensitic microstructure. Density (porosity) and volume (weight) of the components also play a crucial role in martensitic phase formation during sinter-hardening. Understanding the thermal responses of PM materials made at different densities and dimensions is vital to the selection of a suitable sinter-hardening steel with desired mechanical properties.

Previous work characterized the sinter-hardened microstructures of a FL-4608 based material prepared at different density levels with different copper and graphite additions. It has demonstrated that the density has significant effect on the martensite formation when it is above certain density levels. Adjusting the copper and graphite levels can reduce or eliminate the effect of density. In this study, the effect of density and dimensions is further investigated on the phase transformation of material with the same alloying compositions through analysis of thermal responses in the sinter-hardened steels.

034 - Effects of Types of Copper in Cu-Ni-Si Powder Metal
Tyler Stitt, Penn State University, DuBois

CuNiSi is an ideal material for replacing the more toxic copper beryllium alloys. Having good electrical conductivity, high strength and heat conduction, this alloy can be used in a multitude of applications that include valve stems, connectors, fuse clips, and contact springs. Depending on the size and shape of the particles, different types of copper can influence the properties of the Cu-Ni-Si powdered metal (PM) parts. In this study, experimentation was conducted with three types of copper 150A, 200RL, and 150RXM-123 blended with Ni and Si and Caplube W lubricant. The three powders were compacted at the same density and sintered at the same conditions. Tests such as tensile strength, electrical conductivity, and crush strength of the parts were performed in order to compare the properties of these materials with existing copper-based material that is currently used.

921 - SS316L and 17-4 PH bimetallic structures using powder-based laser-directed energy deposition
Aruntapan Dash,  Washington State University

The present research is focused on developing novel bimetallic structures of 17-4 PH and SS316L stainless steels. SS316L powders with particle size 53-150 µm and 17-4 PH powders with particle sizes 15-53 µm are used as feedstock material in a powder-based L-DED metal AM system (FormAlloy, Spring Valley, CA) for printing the samples. Five different compositions, including single and multilayer bimetallic structures, were printed using the feedstock materials with optimized process parameters for each. The printed bimetallic structures have not shown any macro defects. Printed samples were subjected to phase and microstructure characterization. Primarily austenite (γ) and martensite (α) phases are observed in the printed samples. Microstructural analysis revealed the formation of columnar, cellular, and equiaxed dendrites in the SS316L and martensitic structure in 17-4PH. Microhardness and compression tests were performed with these samples to understand how the layering sequence controls the deformation behavior.

073 - High Density Hap and β-TCP Blocks for Biomedical Applications—Fabrication Strategy and Resulting Properties
Helena Pereira, Minho University

Bone has an amazing capability to self-healing, but when a bone defect exceeds the bone's capacity of self-regenerate, grafts are needed and have been used as a solution to these problems. Calcium phosphate-based bone substitutes, such as Hap or β-TCP have been gaining attention, as they have a chemical composition similar to that of human bone. Regardless of presenting excellent biocompatibility, calcium phosphates present low mechanical strength, which is a major drawback for load-bearing applications. In this sense, achieving Hap or β-TCP with increased density is crucial to enhance their mechanical properties. It has been proved that by using pressure assisted techniques such as hot pressing (HP) or hot isostatic pressing (HIP) it is possible to achieve fine microstructures, higher density and improved mechanical properties.
This works demonstrates the fabrication dense blocks of Hap and β-TCP by HP. The obtained blocks were characterized in terms of surface morphology to accesses the grain size differences and porosity. The phase stability of the blocks were also studied as well as their mechanical properties. Results demonstrate that high density blocks of Hap and β-TCP (98.3 ± 0.05 and 99.1 ± 0.59 density respectively) were successfully fabricated by HP and their mechanical properties are suitable for load bearing applications.

076 - Al/Ca DMMC Conductors Powder to Wire, Lab-Scale to Full-Scale
Dustin Hickman, Iowa State University

The ultimate tensile strength and direct current (DC) electrical conductivity were characterized for three Al/6vol.% Ca deformation processed metal-metal composite (DMMC) wires for future use as high-voltage DC overhead transmission conductors.  A unique synthesis of low-temperature solid-state consolidation utilizing a powder metallurgy (PM) route from one-, three-, and twelve-inch billets resulting in several wire samples with five levels of deformation true strain produced competitive, repeatable material properties compared to industrially available overhead conductors. Tensile strength data presented was related to microstructure for all tempers. Conductivity data presented was measured using the four-wire resistance method and related to the composition with respect to the degree of transformation for all tempers, as-drawn and artificially aged. The properties of the resultant wire samples will be compared to the ASTM specification for widely used overhead conductors. Funding from DOE-OE through DE-AC02-07CH11358.

071 - Spark Plasma Sintering and Hot Pressing Al-Sc Sputtering Targets
Ben Zeng, Materion Corp.

One of the most successful piezoelectric materials in electro-acoustic applications is aluminum scandium nitride thin films produced by reactive sputtering from AlSc alloy targets.  The AlScN films are used in the manufacture of the bulk acoustic wave (BAW) filters enabling the current 5G communication revolution.   The AlSc alloy system is very challenging for the manufacturing of sputter targets due to the presence of multiple brittle intermetallics and a propensity for segregation.  Powder processing can overcome many of these issues.  In this study, we utilize powder processing to investigate three alloy compositions with Sc contents of 5at%, 30at% and 50at%, representing a phase structure of Al+Al3Sc, Al3Sc+Al2Sc, and Al2Sc+AlSc.  The alloys were gas atomized, followed by conventional hot pressing (HP) or spark plasma sintering (SPS) to provide a high-density target.  Characterization of the atomized powders, including morphology, microstructure, and chemistry will be discussed. In addition, microstructure, density, hardness, fracture toughness and predominant fracture mechanism as a function of process conditions will be compared for the two consolidation methods.  Sputtering performance will also be summarized. 

069 - Leveraging Design for Additive Manufacturing to Remedy Low Internal Porosity in Metal Powder Binder Jetting
Daniel Juhasz, Waterloo University

Metal binder jetting additive manufacturing (BJAM) is a powerful AM technology capable of producing highly complex metallic parts. However, the high porosity of sintered parts is an ongoing technological limitation, which must be addressed. Previous work with water-atomized 4405 low-alloy steel has suggested a correlation between internal porosity of BJAM parts and the localized reducing potential during sintering, wherein higher porosity is observed at the core of a part due to poor gas flow and subsequent trapping of reduction by-products at these core locations. This poses a significant challenge to obtaining fully-dense parts via BJAM, particularly when trying to sinter large bodies. In this study, we propose addressing core porosity using a design-driven approach. We investigate the feasibility of printing gas flow channels within 4405 low-alloy steel parts and their effects on resulting core density. To this effect, solid body blocks were manufactured with allowance for machining 3 tensile specimens per block, and hybrid lattice/solid blocks were manufactured to encapsulate near-shape tensile specimens in their solid regions. High-resolution computed tomography (CT) data will elucidate the efficacy of enhanced gas flow through the lattice architecture vs. solid block in mitigating entrapped porosity in the gage section of tensile specimens. Additionally, low-resolution CT will elucidate the influence of the solid-lattice boundary interface on geometric fidelity of specimens. Lastly, tensile testing will demonstrate the mechanical performance of the two classes of specimens.

134 - Copper Heat Sinks: Design and Fabrication via Sinter-Based Material Extrusion (MEX) 3D Printing
Kameswara Ajjarapu, University of Lousiville

Copper heat sinks, especially for electronic applications, are typically manufactured using conventional techniques such as bonding, forging, folding, skiving, or machining. Such heat sinks tend to have simple fin/pin structures, partly attributed to the limitations of conventional processing technologies. In this work, we utilize topology optimization to overcome challenges in transforming decade-old traditional sink of heat design using the sinter-based material extrusion (MEX) 3D printing process. In this work, we developed a >90wt.% copper powder-filled polymer filaments to fabricate thermally efficient heat sink designs that were MEX 3D printed and subsequently processed to remove polymer (debinding) and sintered to achieve dense copper parts. It was identified that thick and thin features in heat sinks tend to debound at different rates due to the differences in surface area and amount of binder material that needs to be removed. Although this differential behavior poses challenges with retaining part integrity post debinding and sintering, it can be overcome using techniques such as topology optimization. Therefore, this study looks at understanding the structure-material property relationships behind 3D printing copper heat sinks by MEX-3D printing process by implementing topology-optimized designs that were tested for their thermal efficiency using simulation and experiments.

149 - University-Industry-NIST MEP Partnership for Design and 3D Printing of Legacy Parts a Case Study
Sihan Zhang, University of Lousiville

The overarching goal is to enable rapid, predictable, reproducible, low-cost, and accurate production of legacy metal parts with 3D printing. This work presents a University-Industry-NIST Manufacturing Extension Partnership (MEP) collaboration to enable the adoption of Additive manufacturing technology within industries. Legacy parts that don't have CAD models or design details available are a challenge to the manufacturer to deliver products to their customers on time. In this work, we present the use of 3D scanning and 3D printing to fabricate legacy parts without investing time, effort, and money in making new molds. The University of Louisville-led 3D printing accelerator focuses on 3D printing stainless steel legacy parts to support small manufacturing businesses. At the same time, the NIST-MEP partnership enables surveying the conventionally manufactured parts catalog, creating a business case, and identifying legacy parts that the small company can manufacture with 3D printing. 
For this work, we used a commercially available 17-4 PH stainless steel filament from BASF. We performed 3D printing with MakerBot Method X 3D printer to fabricate legacy parts and compare them with the original parts. The process flow started with creating a model with 3D scanning and CAD software, followed by 3D printing and post-processing to obtain solid metal parts. Comparison with the original details on the dimension and mechanical properties helped fine-tune printing parameters for better replicating the parts to satisfy the customer's needs. 

143 - Advances in Metal Binder Jetting of High Conductivity Pure Cu
Lorenzo Marchetti, Digital Metal

Additive manufacturing of pure copper has been gaining attention from different industries in the consumer, automotive and industrial sectors. Pure Cu components manufactured with traditional methods offer excellent thermal and electrical conductivity, but their performance can be further enhanced with 3D printing by optimizing part geometry, gaining higher effective performance, weight savings and reduced material waste. 
Metal binder jetting (MBJ) allows the production of pure Cu isotropic parts with high conductivity. During printing, a binder is deposited layer by layer on a powder bed at room temperature, allowing the excess powder to be fully recirculated. The part properties are achieved during sintering, where densification occurs.
In order to achieve high levels of thermal and electrical conductivity, it is necessary to rigorously control the powder contamination levels and to achieve a high final component density. Hot isostatic pressing (HIP) can further boost the component performance thanks to porosity-free parts and marginal grain growth.
In this paper, we present the advances of MBJ production of high conductivity parts in the as sintered state and with HIP post processing, modeling their electrical and thermal conductivity based on density, chemical and metallographic analysis.

074 - Influence of Residual Carbon Content on Microstructure and Properties of Copper Produced by Binder Jet
John Reidy, Desktop Metal

Additive manufacturing (AM) of copper components is an exciting area of research, with potential applications in many spaces. Among AM methods, binder jetting is attractive for its high throughput. However, the binder used can leave behind residual carbon in the sintered copper component. In this work, copper parts produced by binder jet printing using a nominally pure copper powder were subjected to a variety of different debind and sintering cycles, resulting two levels of residual carbon and a range of sintered densities. It was found that higher final carbon content led to a finer, less homogeneous microstructure as compared to the population with a lower final carbon content. Additionally, for the population with lower carbon content, pore coarsening was observed at the peak temperature utilized for the parts with higher carbon content. Several lower peak temperatures were investigated for the low carbon content population, resulting in higher sintered density When subjected to tensile testing, it was found that copper parts with high residual carbon levels exhibited much less ductility than those with low residual carbon. 

151 - Microstructural Analysis of Functionally Graded Tool Steel-Copper Composite Produced by Laser Powder Bed Fusion and Pressureless Infiltration
Mahmoud Osman, McGill University

The dies and molds industry broadly relies on H13 tool steel in hot forming applications for its high dimensional and mechanical stability. However, the low thermal conductivity of H13 leads to high cooling time and an overall slow molding cycle. A two-step process has been implemented to produce a tool steel (H13)/Copper functionally graded composite material (FGCM) with tailored thermal and mechanical properties. A variable relative density H13 microlattice was built by laser powder bed fusion, which was followed by their pressureless infiltration by copper melts. The infiltration thermal cycle was designed to incorporate the quenching and tempering cycles of conventionally heat treated H13. The present approach provided an almost fully dense composite material with an optical density of 99.9%. Scanning electron microscope micrographs at the H13/Cu interface revealed full copper infiltration up to the finest sub-micron features of the H13 interface and the absence of interfacial porosities. Energy dispersive X-ray and X-ray diffraction results showed the dissolution of only ~2.2% Fe and ~0.3% Cr in the pure copper matrix after infiltration. A tempered martensite microstructure was observed for H13 zones similar to conventionally heat treated H13, while equiaxed coarse grains of larger than 200 μm were observed for copper zones. The microhardness of H13 after infiltration was measured at 95% confidence interval of 573 ± 5 HV0.5, which slightly exceeds that of quenched and 500°C tempered H13 of 560 ± 8 HV0.5. 

053 - Inconel 718–Copper Bimetallic Joints Fabricated By 3D Multi-Material Laser Powder Bed Fusion for Aerospace Components
Ana Marques, University of Minho

Usually, aerospace components are subjected to high demanding operating conditions in terms of mechanical and thermal stresses. The structural integrity of these components is assured by the use of high strength and temperature-resistant materials such as Inconel alloys. However, these alloys are known to have low thermal conductivity, which makes it difficult to extract heat from inside the component. Copper-based alloys are widely used in the aerospace field due to their high thermal conductivity, high strength, good ductility and corrosion resistance.
 A 3D multi-material Inconel 718 – Copper solution was produced by laser powder bed fusion to be applied on a rocket engine wall aiming to improve its heat extraction ability. This approach combines high strength Inconel 718 and high thermal conductivity Copper in a single part, produced at once. The individual Inconel 718 and Copper zones and interface transition zone features were assessed in terms of metallurgical bonding and mechanical behaviour. This 3D multi-material Inconel 718 – Copper solution seems to be a promising approach since the two materials have a well-defined interface with no substantial defects. Inconel 718 and Copper seems to be capable to maintain its most important individual properties, high strength and high thermal conductivity.

064 - Role of Al Mixing to Prepare Feedstocks for PBF-LB/M to Develop New HEAs via In-Situ Alloying
Jose Manuel Torralba, IMDEA Materials Institute

Manufacturing of high entropy alloys (HEAs) using powder bed fusion-laser beam/METAL (PBF-LB/M) enables their production with minimal elemental segregation due to its inherently fast cooling rates resulting in remarkable properties. So far, HEAs have been fabricated with fully pre-alloyed gas-atomized powders which makes it expensive and slower to explore new alloy compositions. In this work, for the first time, instead of pre-alloying, blended powders of CoCrF75, Ni625, Invar36, and pure Al powders are used to make the final feedstock for PBF-LB/MPBF-LB/M. The processability of this feedstock is explored in PBF-LB/M by fabricating a novel alloy, CoCrFeNiMoxAly, by adding 7, and 9 (in at%) Al. The process was successfully optimized, achieving relative densities greater than 99.8%. The fabricated alloys in as-printed state consisted of predominantly FCC with a minor BCC phase fraction and a homogenous distribution of elements. This method of mixing powders for PBF-LB/M enables rapid exploration of new HEAs. 

119 - Microstructure and Mechanical Properties of Free-Sintering Low Alloy Steel Produced by Three Additive Manufacturing Methods
Tom Murphy, FAPMI, Hoeganaes Corporation

The free-sintering low alloy steel alloy was originally designed for use in binder jet printing applications, which utilizes the finest portion (<25 m) of the as-atomized particle size distribution.  Since only the fine screen cut is used, the feedstock cost is high.  To improve this situation, an investigation was undertaken to expand the market for this dual phase low alloy steel using two additional additive manufacturing processes, thus using a larger percentage of the complete, as-atomized, particle size distribution.   The additional processes were laser powder bed fusion, which uses the intermediate particle size (25-50 m), and directed energy deposition, in which the largest particle size (50-100 m) is deposited.  By using a larger volume of the particle size distribution with three additive manufacturing methods, the feedstock cost is lowered and the market for the dual phase low alloy steel expanded.  The versatility of this multiple transformation product alloy is evident regardless of manufacturing method.  Intercritically annealing samples produces a tailored microstructure that can be modified to fit application requirements.  This is demonstrated with a range of mechanical properties and metallographic analyses from the different additive manufacturing methods.

020 - Cost Effective In-Situ Alloying of Ti-Fe by Laser Powder Bed Fusion
Jeff Huang, Joining and Welding Research Institute, Osaka University

While powder bed fusion AM techniques nominally offer cost reductions in terms of net-near-shape production, the cost of traditional feedstock remains high for pre-alloyed titanium powders. This high cost of entry has restricted the feasibility of powder bed fusion to high-complexity biomedical and aerospace applications. From this perspective, in-situ alloying of cheaper pre-mixed elemental powders offers an attractive means of reducing feedstock costs, with the added benefit of precise compositional design for tailored microstructure and mechanical properties. The present study investigates the in-situ alloying of blended titanium and iron powders via laser powder bed fusion as a means towards developing a low-cost, AM-processable material. The earth-abundant iron is presented as an affordable alternative to conventional but costly rare-earth beta-stabilisers such as vanadium and molybdenum for microstructural tuning. Accordingly, the resulting homogeneity, microstructure, and mechanical properties are comprehensively examined with respect to composition, powder size and processing parameters to identify the critical aspects towards successful in-situ fabrication of economically viable alloys for widespread AM of lower cost applications. 

126 - Microstructure and Mechanical Properties of Wear-Resistant Alloys Produced by the Laser Powder Bed Fusion Process
Kerri Horvay, Hoeganaes Corporation

Hard materials used in applications that require wear resistance typically are difficult to machine. Grinding is commonly used as a forming method, but it limits the part geometries that can be produced. By utilizing additive manufacturing as a forming method more complex geometries can now be achieved with a variety of hard tooling materials. For this study, the additive manufacturing technique laser powder bed fusion was used to process a series of wear-resistant alloys developed to provide a range of properties for different tooling applications. Microstructural and mechanical properties were evaluated for as-built and heat treated samples. Standardized wear testing was performed to correlate the wear resistance to the hardness of the material. The toughness of the materials was also evaluated for applications that require both wear resistance and impact resistance.

522 - Additive Manufacturing of High-Performance Aluminum Alloys for Aerospace Applications
Chloe Johnson, Elementum 3D

Recent advances in alloy design have added to the number of alloys that can be used in additive manufacturing (AM) processes. This is particularly important for aluminum alloys, where complex cooling channels produced using AM can offset the low operating temperature of these alloys for light weighting applications. However, these alloys suffer from solidification cracking in AM due to their large solidification range. One solution implemented in aluminum alloy design for AM is inoculation, which increases grain nucleation, generating a fine microstructure and eliminating hot tearing. Inoculant particles additionally serve as particle reinforcement, particularly with in-situ inoculations processes, where particles initially added to the powder feedstock react in the melt to form inoculants. In this case, both starting reactive particles (if they do not fully dissolve) and finer product inoculant particles can serve as reinforcement. For in-situ inoculated alloys, reactive and product particle type, size, and concentration can be optimized to improve printability as well as optimize certain properties, such as wear resistance, specific stiffness and strength, coefficient of thermal expansion, etc. to improve performance for aerospace applications. This could be important for applications such as Al-Be alloy replacement, where a high specific stiffness is needed without the hazard of processing beryllium materials. Recent advances in design of inoculated aluminum alloys for AM shows the potential to target and improve selected properties to further optimize AM part performance for aerospace applications.

523 - Increasing the Industrialization of Laser Powder Directed Energy Deposition for High Temperature Aerospace Applications
Francisco Medina, University of Texas at El Paso

In the last decade, additive manufacturing (AM) has moved far beyond its original prototyping applications to play an integral part in some companies’ product lines and production approaches. AM of metal components via Laser Powder Directed Energy Deposition (LP-DED) is reaching maturity for aerospace components that can achieve NASA and FAA certification. LP-DED is an AM process in which metal powder is injected into the focused beam of a high-power laser under tightly controlled atmospheric conditions. The focused laser beam melts the surface of the target material and generates a relatively small molten pool of base material. The powder is delivered and absorbed into the melt pool, solidifies after the laser scan continues along its path, and thus generates a deposit. The resulting deposits may be used to Freeform AM or repair metal parts for various applications. LP-DED AM of high-temperature alloys produces nozzle extensions or other large components (e.g., high-temperature radiators, heat exchangers, or hypersonic wing leading edges).

186 - The Importance of Powder Consistency for AM Aerospace Applications
Eric Bono, 6K Additive

As Additive Manufacturing (AM) matures in aerospace, powder quality focus is rightfully shifting from single lot, or point, quality analysis to more holistic consistency considerations.  If the industry hopes to grow into critical applications, powder quality needs to be controlled by specifications and not limited to approving individual lots of powder from specific suppliers.  In order for this transformation to occur, however, powder suppliers and end users must define what consistency means in terms of parameters, values, and tolerances.  This presentation puts forth data that helps define what consistency means for metal powders and what effects that consistency has on final part properties.