PowderMet AMPM Tungsten Special Interest
SESSION P13 MIM Processing
015 - Rapid Tooling Development with Free-Form Injection Molding for MIM
Uffe Bihlet, AddiFab
Metal Injection Molding (MIM) is known for high-volume production of small parts with fine tolerances. The final part geometry is the result of the process parameters of the entire production chain as well as a complex interplay of the feedstock binder system, the powder distribution within parts and the relative sizes and positions of design features. The complexity creates a need for reworks during the tooling design and production phase, which can be both costly and time consuming. A new approach, where 3D-printed, single-use polymer mold inserts allow easy, fast and inexpensive tooling design experimentation. This paper documents a generally applicable rapid tooling development methodology for MIM. The method is validated by production and characterization of 17-4PH stainless steel MIM parts.
001 - Review of Low-Pressure Powder Injection Molding: A Cost-Effective Way to Manufacture Intricate Parts
Vincent Demers, École de Technologie Supérieure
Low-pressure powder injection molding (LPIM) is a cost-effective emerging technology for producing small and complex parts. In this review paper, the capabilities and challenges of this manufacturing technology will be highlighted and compared with the conventional high-pressure approach. Specifically, the recent progress in low-viscosity feedstocks will be highlighted as a key parameter enabling its injection into a mold cavity using an injection pressure as low as 1 MPa, and therefore reducing the overall size for the injection machines and molds. The low cost associated with the LPIM equipment provides an opportunity to fabricate complex shape parts in a cost-effective way, either in low or in high production volumes. Although all the stages of the process such as mixing, injection, debinding, and sintering will be discussed, an emphasis will be placed on feedstock properties and their moldability.
210 - Additive Manufacturing and Numerical Modeling of Injection Mold for Fabricating NdFeB Magnets.
Tejesh Charles Dube, Indiana University - Purdue University Indianapolis
This work presents the fabrication of molds for injection molding of NdFeB based magnets using a novel method which combines powder injection and 3D printing technique. Using customized 3D printed plastic molds, we are able to efficiently manufacture magnets with various shapes. This approach would help in reducing the production cost incurred in the design and manufacturing of magnets and would also increase the productivity. A computational model is built to analyze the design of the mold with respect to the slurry flow. The microstructure and properties of the magnets will be investigated. The magnets produced from this research could serve multiple applications in the medical, electrical, automotive, and aerospace industry.
SESSION P14 Surface Enhancement of Structural Parts
139 - High Pressure Gas Quenching of PM Lean Alloy Powertrain Components Using Latest Generation of Compact Vacuum Equipment
Michael Nemcko, Stackpole International
High pressure gas quenching has been used as an alternative to oil quenching on PM materials for numerous automotive power train components.
The process has been well established with the use of Helium due to its desirable thermal properties, however, supply has been identified as a potential risk. This is directly related to the increased overall demand growing faster than the supply base.
Historically, high volume heat treating equipment has relied on large batch furnaces to achieve economy of scale. In recent years, vacuum heat treatment equipment suppliers have been offering compact furnaces to help improve flexibility and increase the efficiency for the operator. These new furnaces which utilize multiple smaller chambers with up to 20 bar quench capability, justified exploring the use of alternative quench atmospheres with PM lean alloy materials.
A study was developed using available production PM lean alloy components to compare Nitrogen and Helium quench mediums. Identical loads were processed with the same thermal profile and quenched with high pressure Helium and Nitrogen. The Hardness and microstructures were compared throughout the load and within the parts to compare the final properties after quench.
It was established that the use of nitrogen as an alternative to helium gas quench is viable with the latest compact heat treating equipment offering.
074 - Nitriding Mechanisms of Ferrous Powder Metal Products in Gas, Salt and Plasma Methods
Vasko Popovski, Advanced Heat Treat Corp.
Surface hardening of powder metallurgy (PM) products via nitriding can be realized with special precautions, considering the porous nature of such material. Typical response during gas nitriding of PM material (density below 7.3 g/cm3) is through-hardening of product with catastrophic embrittlement. This is because ammonia species tend to penetrate throughout the interconnected porosities, causing internal nitriding. This effect can be minimized/eliminated by pre-oxidizing the material, with formation of an oxide barrier limiting free access to the ammonia. Similar effects can be achieved with salt bath nitriding, but surfaces still suffer from an excessive compound zone.
Plasma nitriding methods can be controlled to avoid this. Nitriding in nitrogen and hydrogen leads to formation of active species such as N2+, N+, NxHy+ ions as well as NH3 molecules and NHx –type radicals. Such ions are neutralized during collisions with the surface, generating active nitrogen atoms which react with it. Their ability to penetrate porosities is limited to near surface distances.
However, ammonia species generated in plasma can go deeply into the structure, similar to what is seen with gas nitriding. Therefore, proper control of plasma nitriding must be utilized for optimizing layer thickness and structure. Plasma nitriding in a mixture of nitrogen and argon eliminates formation of ammonia-type species; the formed layer has a thickness based only on plasma density, temperature, and time. Addition of hydrogen to the plasma leads to formation of the ammonia species; their concentration grows with pressure. In these situations, the nitrided layer can have a greater thickness.
165 - Steam Bluing Process of Sintered Parts Without Using Boiler: A Boon for PM Parts Manufacturing
Ravindra Kumar Malhotra, Malhotra Engineers
A boiler is integral part of Steam Blueing Furnace to supply steam required for the process. There can be an individual small boiler per furnace or a large boiler supplying steam to a battery of Steam Treatment Furnaces whether Batch type or Continue type. The role of steam in the blueing process is to supply Oxygen upon dissociation in to Oxygen and Hydrogen in presence of Iron which is actually the furnace charge. The reaction is reversible therefore creating imbalance of Hydrogen by elimination from reaction location causes oxidation by the left over Oxygen element. Right from inception a boiler has been used for the continuous supply of process steam and the furnace designs were conceptualized based on external steam source. However it requires additional energy as well as extra steam for sustaining transportation losses of heat as well as condensation to water. Any condensate water falling over parts being steam blued causes undesirable brown oxide patches. A steam blueing process which uses water directly without a boiler and converts it to low pressure steam to fill the muffle or retort would be a simple risk-free low energy solution. The steam blueing furnaces need to be redesigned to meet this requirement.
SESSION A16 Metal AM Sintering
049 - Sintering Simulation of Metal AM and MIM Parts Using Growth-Based Generative Design
Andrew Roberts, Desktop Metal
Development of a novel Live Sinter Technique enables the simulation of shrinkage, creep, frictional drag, gravity, and distortion that occurs during sintering, and then automatically produces negatively distorted part to compensate for the distortion to yield a near net shaped component at the end. Live Sinter builds off of Live Parts that utilizes dynamic physics simulation to grow parts similar to how living organisms grow in nature enabling designers to control shrinkage and distortion, reduce support structures, and produce consistent parts. The technology combines both a particle model using position-based dynamics and static finite element analysis to simulate the sintering behavior, and then tunes the process to match scanned sintered part results. Once tuned to furnace and material properties, the technology may be used to simulate and negatively distort parts and supports for subsequent designs and avoid “trial and error” guesswork to sinter the next generation of complex part geometry.
163 - Effects of Reactive Binders on Sintering Binder Jet 3D Printed Materials
Lynnora Grant, Rice University
Nanoparticle and reactive binders are promising materials for increasing the green density and neck size in binder jet 3D printed components. Here we present a ceramic-precursor reactive binder that decomposes to form nanocrystalline necks in the printed compact prior to sintering. Using scanning electron microscopy, we observe the microstructural differences between samples with and without the reactive binder treatment. With a series of dilatometry experiments, we quantified the effect that the increase in interparticle contacts had on creep during sintering and found that the reactive binder treated samples are more resistant to creep. These results are used to develop quantitative sintering and diffusional creep models for binder jet 3D printed materials which integrate our microstructural observations to account for the increase in interparticle neck size introduced by reactive binders.
174 - Gas Flow Optimization in Batch Furnaces via CFD
Nelson Brito, Verder Scientific
In the manufacture of PIM and sinter-based AM parts, heat treatment is still a production step that should not be underestimated in terms of the potential for error. Particularly in debinding and sintering, uneven heat input and inadequate gas flow leads to scrap parts. The decisive factor for a "clean" furnace run is a gas flow in the retort that is as undisturbed as possible - ideally laminar and homogeneous. For this reason, batch furnaces are usually used for the treatment of these parts, which can be used both in atmospheric and, above all, partial pressure. The influence of the pressure on the flow behavior is sufficiently proven. While strong turbulences at and around the components are to be expected in atmospheric pressure (~1000 mbar), these are significantly reduced in partial pressure (~200 mbar). A further influence on the gas flow and the result of a debinding and sintering run is the arrangement of the gas inlet and outlet and the gas distribution in the retort. The aim should be to choose an arrangement that allows a direct, natural flow of the gas. The third factor influencing the gas flow is the arrangement and orientation of the parts, depending on the geometry, in the batch.
For each series startup, several iterations are usually necessary until suitable furnace parameters, an optimal part arrangement and stable series production are found.
This study shall show how all these influences can be visualized, compared and optimized by the use of numerical flow simulation.
SESSION A17 AM Characterization
220 - Similarity Analysis of Thermal Signatures from In-Situ Monitoring of Laser Powder Bed Fusion Process
Sujana Chandrasekar, University of Tennessee, Knoxville
A key challenge to the broad adoption of metal additive manufacturing processes is the lack of understanding about process-structure-properties relationships, primarily due to varying thermo-mechanical cycles that occur in Additive Manufacturing processes. In situ monitoring presents a possible pathway to enable part qualification. In this research poster, a novel similarity analysis method that enables the detection of regions of similar thermal signatures based on infrared monitoring of laser powder bed fusion process will be presented. The algorithmic framework will be discussed and results presented from thermal monitoring of parts, that demonstrate changes in thermal signature associated with part geometry variations. Thermal signature detection is important since the link between cooling rate, thermal gradient and part properties is well-established in additive manufacturing and welding literature. Results showing the generalization of the analysis algorithm to monitoring of thermal behavior in lattice structures will also be presented.
135 - Evaluating the Spreadability of Metal Powders for Additive Manufacturing Applications Using a New Powder Spreadability Analyzer
Gregory Martiska, Mercury Scientific Inc.
The spreadability of several metal powders manufactured for additive manufacturing applications is measured for a range of layer thicknesses under different application conditions including a range of spreading speeds, different spreader geometries, different powder build surfaces, a range of powder feeding geometries and spreader application pressures, and different environmental conditions. A new powder spreadability analyzer was used for the measurements. Presented adata includes spreading efficiency, mass per spreader travel, and spreading uniformity per spreader travel.
134 - Electrostatic Charging and Its Impact on Powder Flowability
Louis-Philippe Lefebvre, National Research Council Canada
It is recognized that the electrostatic charging can affect the flowability of powders. While particle charging is usually more important for nonconductive materials, it has been observed that electrostatic (i.e. coulombic) forces can also affect the flow behavior of metallic powders. Tribocharging is generally associated with the exchange of electrons arising during the friction of dissimilar materials but charging between particles of the same nature has also been reported in the literature. In this context, the interparticle interactions are affected by charge distribution (i.e. the attraction coming from particles having different polarities) which are difficult to measure experimentally. Powder flowability and rheology have recently been used to demonstrate the effect of coulombic forces on particle interaction and flowability. This paper presents an evaluation of the effect of tribocharging on the rheology of different metallic powder (Inconel 718, aluminum, titanium, stainless steel). Results show that the nature of the materials is important and may affect significantly the rheology of the powders.
SESSION A18 Metal AM Post Build Operations
117 - Print Faster in Powder Bed Fusion Ti-6Al-4V Using Hot Isostatic Pressing (HIP)
Chad Beamer, Quintus Technologies
Improvements with AM technology offers near maximum density in the as-printed condition. Despite these advancements the structure exhibits defects having a negative impact on properties. Consequently, AM parts often receive a Hot Isostatic Pressing (HIP) post-process. HIP offers a route to heal such defects, improving properties. With Powder Bed Fusion (PBF) technologies being a slow and costly process, a fair question can be raised; “What is the advantage of printing to maximum density prior to HIP?”. HIP can enable the ability to print with increased build rates. The output is a structure with a lower density, yet the porosity can be addressed with HIP. This paper will capture a number of studies exploring two approaches. One approach incorporates increasing scan speed of the beam and/or the hatch spacing for higher print speeds. Density, micrographs, mechanical testing results and time savings will be reviewed, highlighting the ability to reduce print process time without sacrificing quality. The other approach involves a shelled concept. This method applies laser melting to only the outer shell of a structure. In this case the interior of solid shells of varying thicknesses contain intentionally-unmelted powder. HIP is then applied to fully consolidate the unmelted powder. Resulting microstructure, mechanical testing, and process simulation will be reviewed. The learnings on minimum shell thickness and shrinkage ratio are then incorporated into a design. Data shows comparable mechanical properties to that of a fully dense printed component while yielding less production time and energy consumption.
022-R - Effect of Heat Treatments on Mechanical Properties of Ultra-High-Strength Maraging Steels Fabricated by Additive Manufacturing
Faraz Deirmina, Sandvik Machining Solutions AB
In Metal Additive Manufacturing (metal AM) processes, especially laser powder bed fusion (L-PBF), there are many parameters that affect the microstructural development and consequently mechanical properties of built parts, such as thermal history, non-equilibrium solidification structure and meta-stable phase formation. These microstructural features can have a remarkable influence on the mechanical properties of parts after post-processing heat treatments. Generally, rapid solidification enhances the strength as a result of sub-structure refinement and increased dislocation density in martensitic steels. More importantly, non-equilibrium solidification might result in suppression of unwanted phase precipitation. However, inter-cellular micro-segregation accompanied by fast, non-equilibrium solidification might result in the formation of retained austenite, preferentially located at the cellular boundaries, which can affect the strength of maraging steel. Moreover, the presence of these phases might influence the aging (tempering) behavior. In this work, we report the effects of adapting different heat treatment strategies on the hardness, tensile strength, impact toughness and fatigue behavior of two different classes of ultra-high strength AM maraging steels aimed at achieving 54 and 60 HRC hardness levels.
246-R - 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.
SESSION T06 Hardmetal III
216 - Synthesis and Consolidation of CoCr+X (X=SiC or WC) Milled Powder for Additive Manufacturing
Madelyn Madrigal Camacho, University of California, Riverside
The field of metal additive manufacturing (MAM) is rapidly advancing; however, it faces several challenges including the development and production of new alloy systems and powder composite manufacturing methods. Previous studies have investigated metal matrix composites produced by selective laser melting (SLM) which resulted in finer grains, improved hardness, and tensile strength due to the homogeneous distribution of reinforcement particles. To address some of the challenges in alloy development for MAM, this work has the intent to investigate ball milling technology and its capability of producing printable powder. Additionally, in order to obtain equiaxed, fine grained microstructures and provide useful guidance to achieve better mechanical performance for Co-Cr parts, the incorporation of carbides and their precipitation at atomic scale during the laser sintering is studied using pulsed and continuous laser. The observations point to the applicability of high energy ball milling as a platform for alloy and composite design for MAM.
182 Wear Phenomena in Different Cemented Carbides During Rotary-Percussive Drilling in Reinforced Concrete
Steven Moseley, Hilti AG
Rotary-percussive drilling through steel reinforced concrete not only subjects cemented tungsten carbide drill bits to intensive abrasive wear but additionally induces significant microstructural changes in the near-surface regions. These include micro-, meso- and macroscopic cracking; comminution of the WC; delamination of WC-binder interfaces; binder depletion and pore formation; partial WC dissolution and rearrangement; surface decarburization; and the creation of secondary phases within the binder.
In this study, the wear phenomena in cemented carbide drill bits with different WC grain sizes (fine to extra coarse), binder contents (6-12 weight %) and binder types (Co, Co-Ni and Ni) have been documented, analyzed and quantified. Noticeable differences between the various grades are evident.
A wide range of experimental variables have been investigated covering the large proportion of real-world cases encountered in the application of these drill bits on the construction site. This paper presents a broad overview highlighting how material choice influences wear.
021 - New Environmentally Friendly Carbon Black and Tungsten Carbide Products
Ned Hardman, Monolith Materials
Carbon black producers in the market today are utilizing decades-old production methods which have a significant negative environmental impact. In addition, these methods have proven to be energy-intensive while also being highly inefficient. A new entrant into the industry has developed a patented process for producing carbon black from natural gas and electricity. This new process is driven by a new, innovative, responsible technology that disrupts the antiquated, unsustainable and environmentally harmful incumbent method. The patented process enables natural gas to be converted to specifically targeted grades of carbon black at similar purity levels to thermal black. First stage testing of the carburization of tungsten powder was conducted using several carbon black grades. The testing revealed differences in reactivity of the various carbon grades. A comparison between thermal black products from the carburization process shows similar performance in terms of conversion rates and sintered properties.
Special Interest Program Abstracts
SIP 2-3 Alan Lawley Memorial Symposium III: Stainless Steels
575 - The Allure of Stainless Steels Produced by PM Technology
Chaman Lall, MPP
Stainless Steels are a class of materials offering the allure of longevity in service, essentially unaffected by the corrosive effects of most naturally-occurring elements in the environment. Synthesized and created by man, this class of materials attempts to retain the shining beauty of metals, replicating the characteristic beauty of a metal found in nature- gold. Stainless steels beyond their silver beauty, can be customized to promote strength which opens up the opportunity to use such materials for high performance structural applications. The 2008 “Outstanding Paper of the Year” co-authored by Prof Alan Lawley summarized the results of combining austenitic, martensitic, and precipitation hardening stainless steels. The dual final phase microstructures in this customized stainless steel culminated in a unique combination of high strength, ductility, and corrosion resistance. The dual phase stainless steels resulting from this powerfully important study set the stage for new load- bearing applications that can also be expected to retain their stainless looks for a long time. In this commemoration of Prof Alan Lawley’s contribution to the Powder Metallurgy (PM) Technology, a brief review of stainless steels will be presented.
553 - PM Stainless Steel: From Press-and-Sinter to AM
Alberto Molinari, FAPMI, University of Trento
The paper presents an analysis of the main issues related to the production of stainless steel parts by Powder Metallurgy. Three processing routes are considered: Press-and-Sinter (PS), Metal Injection Moulding (MIM) and Additive Manufacturing (AM).
In PS, the role of porosity on the corrosion resistance and the effect of interstitial content on the microstructure, on corrosion and mechanical resistance and on magnetic properties will be discussed. The contamination by interstitials is mainly related to the interaction with the sintering atmosphere, which will be shortly analysed. Moreover, the influence of the interstitial content on sintering shrinkage will be discussed, in particular when 17-4PH stainless steel parts are manufactured by MIM.
Different phenomena occur during processing through AM. In Powder Bed Fusion, the large undercooling generates either ultrafine or metastable microstructures, whose effect on the properties will be analysed. Conversely, the new emerging technology based on BinderJet 3D printing has several similarities with MIM. The microstructural quality depends on the control of the contamination during debinding and sintering, and the subject will be discussed in relation to the atmosphere used during these two steps.
567 - Microstructure Development in Dual Phase Stainless Steel Parts Made by Laser Bed Powder Fusion
Thomas F. Murphy, FAPMI, Hoeganaes Corporation
Dual phase stainless steel alloys are characterized by a ferrite-martensite microstructure that is usually formed through a secondary heat treatment after creation of the part. The heat treatment requires reheating the part into the ferrite-austenite region of the phase diagram, creating partitioning of the alloying elements into the two phases. This is followed by rapid cooling, which transforms the austenite at high temperature to martensite. It will be demonstrated that the as-built parts made by laser bed powder fusion do not have the dual phase microstructure because, when building parts by heating with the laser, the cooling rate experienced by the parts in the powder bed is too rapid for the alloy partitioning to occur and consequently, the dual phase microstructure is not transformed. In order to create the desired two-phase microstructure, experiments are made with several heat treatments, which result in variations in the proportions of the ferrite and martensite phases after cooling. The resulting differences in microstructure and alloy distribution are investigated with the corresponding changes in physical and mechanical properties caused by variations in heat treatment temperature.