PowderMet AMPM Tungsten Special Interest
SESSION P22 Sintering Mechanism
099 - Sintering Shrinkage of Plain Iron and Austenitic Stainless Steel: The Role of the Structural and Geometrical Activity
Silvia Baselli, Università degli Studi di Trento
The dimensional changes in sintering of uniaxially cold compacted green parts are anisotropic in consequence of the geometrical and structural modifications introduced by prior cold compaction. Particularly, the powder particles are in contact over a surface and the dislocation density in the interparticle contact regions is higher than that of the starting powder (annealed condition).
To clarify the role of the geometrical and structural activity, as well as that of the thermodynamic driving force in this context, a dilatometry study has been carried out on plain iron and austenitic stainless steel.
The low volume diffusivity (due to the fcc structure) which makes necessary a high sintering temperature to register a shrinkage and the absence of the transition from ferromagnetic to paramagnetic behavior make it expected that the structural activity is much less relevant for AISI 316L. The peculiar aspects and the main differences respect to iron will be highlighted.
094 - Nanophase Separation Sintering in Refractory Metals
Christian Oliver, Massachusetts Institute of Technology
Nanophase separation sintering (NPSS) facilitates low temperature, pressureless sintering for refractory materials such as W and Mo. Here we evaluate the NPSS of W-Cr and Mo-Cr alloys, and compare master sintering curve analysis with a more detailed view of the densification rate as a function of temperature. This analysis reveals two periods of significant activity during the sintering process: 1) an initial low-temperature peak in densification rate corresponding to neck formation and 2) a small secondary peak leading to a rapid increase in densification rate. A Kissinger analysis of these peaks gives activation energies associated with those processes, which are combined with microstructural observations to understand the structural evolution during NPSS. We find that both the phase separation as well as the second phase redissolution are associated with sintering acceleration, with the onset of sintering relying on the diffusion of the sintering aid through the base element (Cr though W or Mo), but the majority of the densification controlled by diffusion of the base metal.
212 - Parametric Study of Al-7075 Alloy Sintering Process
Saber Nemati, Louisiana State University
Nonhomogeneity, geometry distortion, and high porosity are common defects in additively manufactured metallic parts. This paper examines the sintering process of Al-7075 alloy AM parts using numerical simulations, validated by experimental tests. A model is established and validated numerically against experimental data in order to evaluate the contribution of diffusion mechanisms in the sintering process in different stages. This model is then implemented in a Finite Element commercial package to predict the final physical and mechanical characteristics of AM parts with more complex geometries. Subsequently, the numerically optimized design is manufactured and tested and the results are compared to those of predicted by the simulations. The approach presented in this paper is capable of optimizing the design and control parameters for the sintering process, to achieve a high quality in terms of strength, geometrical consistency and homogeneity at the end.
198 - New Die Wall Lubrication Process for Warm Tooling Compaction
Brad Morningstar, MPP
199 - Shot Peen for Enhanced Fatigue Properties in PM Gears
Steve Wendel, Catalus Corporation
200 - Rust Prevention of PM Parts
Arthur E. Jones, Symmco, Inc.
SESSION A28 Sinter Based AM Part II
160 - Addressing Powder Morphology and Filament Properties for Extending PIM Feedstocks to Fabricate Green and Sintered Alumina Parts via Ceramic Fused Filament Fabrication (CF3)
Kameswara Ajjarapu, University of Louisville
In this work, a hybrid ceramic fused filament fabrication (CF3) 3D printing process that combines fused filament fabrication (FFF) and sintering processes was used to fabricate highly dense alumina specimens. Spherical and irregular alumina powders were used to prepare highly loaded powder-filled polymer feedstock filaments to determine how powder morphology and filament properties affect 3D printing and the ensuing properties. Rheological, mechanical and material properties of extruded filaments, 3D printed green and sintered alumina specimens were studied. Feedstock viscosity, elastic modulus and shear strength were measured as a function of temperature and shear rate, and correlated with standard powder injection molding (PIM) feedstocks. Further, filament integrity was predicted and experimentally determined to identify how printability and mechanical properties of CF3 3D printed specimens scale from green to sintered state. It is expected that such a method will enable the transition of PIM feedstocks for manufacturing ceramic components via CF3.
026 - Additive Manufacturing of Fe-Si Soft Magnetic Materials
Kalathur Narasimhan, FAPMI, P2P Technologies
3D printing, additive manufacturing, has attracted significant attention recently as a technology that allows three dimensional shapes to be formed. Binder jet, Ink jet, printing are popular process that can compete favorably with injection molding and polymer bonding .Lasers provide a unique opportunity to heat small area of powder, typically 20 to 40 microns, and the melt cools rapidly. The cooling rate is fast enough to form fine grained microstructure. In the case of hard magnetic materials this cooling rate allows the opportunity for the formation of nearly single domain grains .In the case of melt spun Neodymium iron boron ,selective lase meting (SLM) can be used to make bulk magnet fully dense bodies which otherwise not possible by melt spun ribbons. Ribbons need to be crushed and blended with polymers to shape magnet bodies or hot formed to make dense magnets. Soft magnetic materials also can formed by SLS. This paper explores the opportunity for 3D printing for magnetic materials.
164 - Effect of Bimodal Powder Distribution on Mechanical Properties of Ceramic Fused Filament Fabrication (CF3) 3D Printed Hydroxyapatite and Silicon Nitride Biocomposites
Kavish Sudan, University of Louisville
In this article, we report the fabrication of hydroxyapatite (HAp) and its composites with 7.75 vol% Si3N4 using ceramic fused filament fabrication (CF³). Homogeneous feedstocks with 75 wt% ceramic powder were prepared and used to extrude filaments for further printing using a desktop printer. The presence of Si3N4 creates a bimodal powder particle distribution within the matrix which affects the rheological behaviour of the feedstock in the green stage, as well as the resulting microstructure in the sintered stage. Our results show 70% reduction in grain size and substantial improvement in hardness values attributable to the bimodal powder distribution. A DOE was conducted during the 3D printing stage to study the process-parameter relationship for highly filled filaments and to establish guidelines for high precision printing for similar systems. The printed parts were then subjected to solvent debinding followed by sintering to obtain dense ceramic parts. With this research, we aim to uphold CF¬3 as a novel additive manufacturing process capable of exploiting the benefits of bimodal powder distribution and precise fabrication of complex bioceramic parts suitable for biomedical implant applications.
SESSION A29 Multi-Materials
059 - Multi-Material Manufacturing with Direct Metal Deposition (DMD)
Bhaskar Dutta, DM3D Technology, LLC
While existing manufacturing technologies are unable to synthesize a single part with multiple different metals, AM technologies based on directed energy deposition (DED) techniques can manufacture multi-material components. Direct Metal Deposition (DMD) is one such technique that uses its multiple hopper technology and integrated CAM software to deposit different materials at different locations on a given part. The ability to add multiple materials in the same layer and/or in different layers lends it as a great tool for value added manufacturing and allows fabrication of high performance components with functional properties. This presentation will give a brief overview of the DMD technology highlighting the benefits of the process, discuss the materials, microstructures and properties. Three specific case studies involving copper-steel, steel-Inconel, and steel-stellite system will be illustrated to demonstrate multi-material component fabrication for tooling industry, space industry and others. Strategy of material selection, processing challenges and test results will be shared.
246 - Highlights of Copper Development for Binder Jet: Porosity Control for Metal Filters, Nanoparticle Enhancements, Isostatic Pressing and Oxidation Control
Patrick Dougherty, ExOne
Binder jet additive manufacturing (AM) has a number of unique advantages compared to other AM techniques including more traditional microstructure , ability to handle a wider range of materials, and faster throughput which leads to much lower cost at production volumes. Pure copper is a high-value material due to its thermal and electrical conductivities, and recently also due to its antiviral properties in light of the COVID-19 virus. While the sintering process inherent to binder jet should make processing easier than with other AM techniques like EBM and DMLS, copper has its own unique challenges in the green state which have so far prevented fully dense binder jetting of copper. In this work, several techniques will be presented for enhancing the density and material properties of binder jet copper, as well as an application in which the unique aspects of copper can be to create a partially sintered, porous metal filter for airborne particulates.
005 - Functionally Gradient Materials: The What, How, and Why
Michael Juhasz, FormAlloy
Functionally Gradient Material (FGM) systems allow gradual material transitions with lower residual stresses from one material to another. FGMs create potential to improve properties, such as strength or corrosion, and Directed Energy Deposition (DED) is a prime AM technology to allow its users capitalize on the FGM benefits. Considerations in design attributes, chemical compositions, and microstructure can be developed to achieve the best material properties where the need is most critical. Learn about how a DED OEM approaches FGM design with powder-fed systems and OEM Solutions. With the wide range of materials available in powder form and with the continuing advancements within the 3D printing technology space, the ability to produce multi-alloys or gradients within a single build is possible. How DED is used for multi-material/functionally graded material components, and the utilization of a new powder feed system to accelerate the adoption of graded materials will be presented and discussed.
SESSION A30 Atomized Feedstock for AM
068 - Tactics for Optimizing Gas Atomization
Liang He, Air Products and Chemicals, Inc.
The atomization of metal melts is a highly effective method to produce high quality fine metal powders. However, because of the complexity of equipment and process, the production cost is still relatively high, especially on the industrial gas consumption. Hot gas atomization used pre-heated gas to atomize the liquid metal stream. This technique is used in the production of finer metal powder with decreased gas consumption. In this article, AISI 316L stainless steel powder was produced with high pressure nitrogen at different pre-heating temperature. Gas to metal ratio, powder diameter, powder fluidity, and oxygen/nitrogen pickup are measured. The results show that hot gas atomization can produce high quality metal powder for PBF additive manufacturing process with less gas consumption.
148 - Comparative Study of Gas and Water Atomized AISI 4340 in Laser Powder Bed Fusion
Allan Rogalsky, Multi Scale AM Lab - University of Waterloo
A limited body of literature has established the printability of water atomized (WA) powder in laser powder bed fusion (LPBF) with respect to part density. This work studies the impacts of two powder production methods, WA and gas atomization (GA), on part characteristics for the AISI 4340 alloy. To achieve this comparison, a process parameter window for GA powder which resulted in a part solid fraction between 99.6 and 99.98 %, a top surface roughness between 3.8 and 9.9 μm, and a side surface roughness between 15 and 22 μm was deployed for WA powder. The results are discussed in relation to powder qualities namely: powder size distribution (PSD), particle morphology, tap density,
dynamic angle of repose, cohesive index, and laser absorptivity. These play an important role in the mechanisms driving part quality differences leading to recommendations for future performance improvements when using water atomized feed stock.
177 - 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 T10 Novel Materials
157 - Precipitation Hardened Refractory Chromium-Based Alloys: An Overview on Alloy Development
Mathias Galetz, Dechema Research Institute
Refractory alloys such as the Mo-Si-B family and Nb-silicide based alloys have been investigated as candidate materials for application temperatures beyond nickel-based alloys. All refractory alloys offer high melting points along with promising mechanical properties at high temperatures. Chromium was also reconsidered as a base metal, because its lower density compared to Ni and body centered cubic structure offering high thermal conductivity, high oxidation resistance along with high availability and thus competitive pricing. The main drawbacks that led researchers to abandon chromium are a ductile to brittle transition temperature (DBTT) above room temperature, poor oxidation at ultra-high temperatures (T>1000°C) due to the severe nitrogen embrittlement of non-alloyed Cr and the formation of volatile oxides. In this work, different very promising alloys with A15-silicide forming elements Silicon plus Platinum and Germanium and Molybdenum and their major impact on the microstructural evolution, creep and oxidation resistance are presented.
193 - Dispersion Strengthened Mo and Mo-W Alloys for Nuclear Thermal Propulsion
J. Scott O'Dell, Plasma Processes
Refractory metals such as molybdenum (Mo) and molybdenum-tungsten (Mo-W) are desired for nuclear thermal propulsion (NTP) components such as claddings and cermet fuels. Due to high temperature exposure during fabrication and service of NTP components, significant grain growth can occur resulting in large refractory metal grains, which reduce mechanical properties. Therefore, during this effort, dispersion strengthened (DS) Mo and Mo-W alloys were investigated, and specific emphasis was placed on the development of a thermodynamically stable dispersoid phase that was tailored for NTP, i.e., no detrimental neutronic effects. To produce samples for evaluation and demonstration of near-net-shape formed claddings, Vacuum Plasma Spray (VPS) forming techniques were used. Microscopic examination showed fine grain microstructures were retained for the DS Mo and Mo-W alloys after high temperature exposure. Properties testing revealed significant improvements in ultimate tensile strength (UTS) and yield strength (YS) for the DS Mo and Mo-W alloys as compared to pure Mo at room and elevated temperatures. Elongation and reduction in area increases were also observed for the Mo alloys at room temperature; thus, significant improvements in strength and ductility were achieved by producing fine grain structures. These results will be discussed in this paper.
202 - The Effect of Powder Properties of Sintered CuNiSi Powder Metal
Nicolette P. Brossard, Pennsylvania State University, DuBois
Copper-beryllium alloys are most favorable materials for high power-density engine parts, such as valve guides, valve seats and piston rings, due to their relatively high conductivity and low friction. These materials offer superior combination of strength, thermal conductivity, thermal expansion coefficient, wear and friction properties, fatigue limit and corrosion resistance. Unfortunately, beryllium containing metals can cause lung disease and they are increasingly discouraged from use, particularly in the European Union. This has led to an increasing interest in copper-nickel-silicon alloys for replacing traditional copper-beryllium for applications requiring high strength and good conductivity. In this presentation, we are reporting key properties of heat-treated Cu-Ni-Si powder metal premixed with minor alloying elements of chromium and magnesium.
Special Interest Program Abstracts
SIP 3-3 Flow and Spreadability Characterization of Metal Powders III: Powder Rheology Testing Using the Freeman FT4 Rheometer
577 - Blind Testing of SS-316L Metal Powders Using the Freeman FT4 Rheometer
Roger Pelletier, National Research Council Canada
Four samples of a SS-316L powder representing virgin feedstock as well as material that had experienced multiple machine cycles in a laser-beam powder-bed-fusion process were supplied to three participating laboratories where they were tested for various dynamic and bulk property measurements using a Freeman FT4 rheometer. The interlaboratory study was aimed at determining the discriminating capability, test repeatability and reproducibility of the tests. The participants did not know which of the powders samples represented virgin or used material. Each laboratory was requested to perform three repetitions on fresh test portions of each of the four powder samples. The test results from each of the three participants are summarized in this presentation.
552 - Assessing the Robustness of Powder Rheology Measurements
Louis-Philippe Lefebvre, National Research Council Canada
Powder metallurgy processes rely on powder flowability. However, flowability is not an intrinsic property and depends on the measurement conditions. Standards have been developed to adjust measurement methods to various flow conditions but there are presently questions whether current methods are adapted to the specific requirements of powder-bed additive manufacturing. Rheology has been used to assess powder flowability but there is still limited information available about the factors that are affecting the measurements. This paper presents the effect of different factors (powders, charging, humidity, procedures and set-up) on the rheology of powders.
245 - Exploring the Effects of Metallic Powder Handling and Storage Conditions on Flowability and Moisture Content for Additive Manufacturing Applications
Jack Grubbs, Worcester Polytechnic Institute
Metal powder-based additive manufacturing (AM) processes have become increasingly popular in academia, government, and industry over the past decade. While often overlooked, the success of these AM processes is determined largely by the quality of the feedstock powder utilized. Powder properties, such as flowability and moisture content, are essential to maintain at a suitable level to ensure predictable behavior during processing. A common path to property degradation with metallic powders is repeated exposure to ambient conditions during powder handling and storage, which may affect the processability of the powder using AM techniques. Therefore, it is critical to understand how environmental exposure of metallic powders during handling and storage can affect the feedstock’s properties. It is the aim of this work to explore the effects of repeated environmental exposure during powder handling and storage on the flowability and moisture content of aluminum 5056 and tantalum powder for use in AM applications.