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Tuesday Sessions
3:45 p.m. - 5:00 p.m.

PowderMet          AMPM          Tungsten          Special Interest

PowderMet Abstracts



SESSION P15   Progress Toward Full Density


066 - A Combined Multiphase-Field/Discrete-Element Method for Sintering of Blended Elemental Powders
Kazunari Shinagawa, Kyushu Univeristy

As a method for producing alloy parts by powder metallurgy, blended elemental powder processing has been developed to attain cost-saving and reducing forming load.  It can also be used to fabricate heterogeneous materials, which may result in enhanced strength and toughness.  The formation of heterogeneous microstructure, however, is affected by the size, the amount, and the distribution of the elemental powder particles, and they should be controlled to obtain the optimized mechanical properties.  In this study, a method for simulating the diffusion of elements and the phase transformation during sintering is proposed.  As a model system, a binary eutectic alloy is assumed, and the interdiffusion and the liquid formation between different two particles are simulated by a multi-phase-field method for sintering.  The discrete-element method is also conducted to compute the sintering shrinkage with taking account of the contact area and the sintering force, obtained from the phase-field.

070 - Variation of Double Press Double Sinter to Produce High Density Low-Alloy Steel Parts 
Harb Nayar, FAPMI, TAT Technologies LLC

Considerable work has been carried out using double press double sinter route to produce low-alloy steel parts in the 7.3-7.5 g/cc density range. These parts are heat-treated to further enhance the mechanical properties.
 This paper will review the past work and present an alternative route of Double Press Double Sinter starting with 100% pre-alloyed as water atomized low alloy steel water. Two un-annealed water atomized -60 mesh powders in two compositions were used as the starting powders in this study. The compositions were Mo and Cr alloys with and without 0.5% carbon.   TRS bars will be used as the parts in this study to get to 7.3-7.5 g/cc final sintered density.

155 - The Effect of HIP on the Microstructure of Metal Injection Molded 718
Rees Jones, ARC Group Worldwide

Alloy 718 is a nickel-based superalloy that is used extensively in aerospace for demanding high-temperature applications. The complex multiphase microstructure required to obtain suitable mechanical properties is highly dependent on the thermal processing history of the part.  Hot Isostatic Pressing is used in casting and MIM to achieve near-theoretical densities on finished parts.  Previous investigations were performed to characterize the evolution of the alloy microstructure of metal injection molded 718 at different sintering temperatures. In this study, additional sintering temperatures above the solidus were examined.  Parts at various sintering temperatures also underwent Hot Isostatic Pressing.  The resultant microstructures were characterized using traditional micrographs and scanning electron microscopy.  Density and microporosity were also evaluated and compared to pre-sinter results.


SESSION P16   Enhanced Kinetics and High Temperature Sintering


138 - The Effect of Elevated Sintering Temperature on the Microstructures and Mechanical Properties of Low Alloy PM Steels 
Jordan Kramp, Stackpole International

The effect of increased sintering temperatures (>1300°C) was explored and benchmarked against conventional (~1100°) and high temperature sinter (~1300°C). 

Selected lean alloy PM admixed steel compositions were used with consideration to hardenability requirements, in neutral hardening and carburizing heat treatments. 

PM steels were subject to microstructural and physical characterization including final attained sintered density, apparent hardness and mechanical rupture strength, as well as dimensional change.  Pore morphology development over the temperature ranges was characterized by optical image analysis. Wavelength-Dispersive X-Ray Spectroscopy (WDS) elemental mapping was used to semi-quantitatively compare differences in diffusion and material homogeneity. 

Test bar data and laboratory component tests show the relative fatigue durability performance of the PM material sintered at different temperatures.

It is shown that to improve component durability, increased sintering temperatures may be an enabling technology to improve the endurance limits of powder metal components.

222 - Thermodynamically Consistent Formulation for Phase-Field Simulation of Sintering
Rui Dong, University of Utah

Sintering is the most common technique in powder metallurgy, but it has been challenging to study the kinetics of part densification and grain coarsening during sintering. In this work, we develop a phase-field model with a thermodynamically consistent formulation to simulate the particle coalescence and grain growth. Thermodynamic descriptions from the CALPHAD database and dimensional material properties (free energy, diffusion coefficient) can be directly used in  this formulation. Furthermore, we perform a series of sintering experiments of pure copper to validate our model. The details of sintering kinetics are then investigated with the simulation results.

154 - Ultra-High Temperature Sintering, the Benefits and Potential PM Opportunities
Francis Hanejko

High temperature sintering of low alloy ferrous materials is considered to be sintering done in the range of 2125 F to 2300 F.  Recently, experimental work was carried out that investigated the potential benefits of sintering at temperatures approaching ~2500 F.  This ultra-high temperature sintering enhances the many advantages of the current high temperature sintering with added benefits of even greater mechanical properties and the greater utilization of non-traditional PM alloying elements.  At these ultra-high temperatures, the diffusion rates of elemental additions are significantly enhanced; thus, the potential exists to utilize high compressibility iron powders with elemental alloying additions, yet still achieve complete alloy homogenization within the sintered compact.    Mechanical properties of the ultra-high temperature sintered alloys exhibited ultimate tensile strengths exceeding 210,000 psi with elongations approaching 2% at a sintered density of ~7.1 g/cm³.   This combination of strength and ductility are superior to any current ferrous PM material.  What will be reported on in this report will be the unique alloying additions, processing details and the resulting mechanical properties along with a metallographic analysis of the resulting ultra-high temperature sintered ferrous material


SESSION P16   Enhanced Kinetics and High Temperature Sintering


039 - Improved Design and Evaluation of An Extrusion Based 3D Bioprinter
Jing Zhang, Indiana University - Purdue University Indianapolis

204 - Sinker EDM of AM Parts
Kelsey Lee Mickelson, California Polytechnic State University

The purpose of this research is to study the parameters of sinker electrical discharge machining (EDM) to optimize the surface finish of additively manufactured parts. Currently, there is lack of studies that investigate how the sinker EDM can be utilized for post processing of AM parts. Through this research, parameters that influence surface finish will be studied. An AM test coupon that will be printed from 316L stainless steel, will be utilized to evaluate various EDM parameters. Surface roughness was characterized using a confocal microscope. Preliminary study indicated that the as printed surface roughness was between 500 to 600 micro inch; after sinker EDM, the surface roughness was improved to 170 micro inch. In the future, more complex geometries will be studied.

208 - Application of Polymer Coating on Additively Manufactured 316L Stainless Steel
Xuehui Yang, Indiana University - Purdue University Indianapolis

In order to improve the corrosion resistance of additively manufactured (AM’d) 316L stainless steel (SS), we applied polymer coating on the steel. One of the potential applications of the work is to use the coated steel as implants. However, currently, there is very limited research was conducted in this field. In this work, the microstructure and mechanical properties of polymer coated AM’d 316L SS are studied by a combined experimental and modeling method. For the experimental part, AM’d 316L SS samples are fabricated using a laser powder bed fusion process. Then epoxy is coated on the AM sample surface. For comparison, a wrought 316L SS sample is also coated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are employed to observe the characteristics of coated samples. For the modeling studies, molecular dynamics (MD) is used to simulate the interface between the polymer and metal. A simulated tensile test is conducted to evaluate the mechanical properties. This study may provide important information for extending the AM metals in applications where corrosion resistance is needed.

AMPM Abstracts



SESSION A19   Novel AM Applications


149 - Impact of Sinter-Based Metal Additive Manufacturing on Metal Injection Molding
Animesh Bose, FAPMI, Desktop Metal

The emergence of Sinter-based metal Additive Manufacturing (AM) technologies is expected to spur an unprecedented growth in the area of metal AM. These Sinter-based processes offer significant advantages over melt-based metal AM technologies. Similar to metal injection molding (MIM),  bound metal disposition (BMD) is based on the material extrusion process like fused filament fabrication (FFF) and is meant for rapid prototyping and low volume serial production, while the binder jetting (BJ) process addresses high and medium volume production of metal parts. Both have the advantage of freeform fabrication of metal parts without any tooling and are expected to have a significant impact on MIM technology in different ways. This paper will discuss the two Sinter-based AM platforms and explore their impact on MIM technology.

161 - 3D Printing of Permanent Magnets
Kalathur Narasimhan, FAPMI, P2P Technologies

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.

115 - Advantages of AM to Precious Metals Applications
Jochen Heinrich, C. Hafner GmbH + Co KG

As we still learn about pros and cons of the relatively young and emerging technology of additive manufacturing, precious metals represent a long history rich in tradition, handcraft, artisanry, emotion and value. The potential of the combination of additive manufacturing and precious metals might be different to non-precious metal processing and therefore not obvious at a first glance. Considering the significance of freedom of design, economical aspects and variety of materials is certainly of great importance for manufacturing of precious metals applications.
This paper gives an insight into the processing of precious metals powders by laser fusion. Selected applications show the particular advantages of additive manufacturing of precious metals covering unique jewelry design possibilities, efficient production with regard to lot size and material input as well as unleashing materials and their special properties unthinkable in the world of casting metallurgy. And it’s not all about jewelry and luxury goods. Think of properties like high resistance to temperature and/or corrosion as well as biocompatibility and you end up with new opportunities for technical or medical applications!


SESSION A20   AM Part Characterization


158 - Density Verification of Cubes Produced by Direct Metal Laser Solidification (DMLS)
Bryce Christensen, GKN Sinter Metals

The advantages of metal additive manufacturing (AM) make it an attractive alternative to conventional processing techniques when intricate parts are needed. Scaling AM to a production capacity comes with unique challenges. One of which is the need for density verification of the printed parts which is often done with the use of density cubes. These 10x10x10mm cubes act as coupons for printed parts. In research and development of new printed materials, it’s important to check these density cubes for excess porosity via image analysis. However, in a production climate, this slows down production due to the need for sample preparation. This paper explores the option of using Archimedes density for density verification of metal additive manufactured parts produced via direct laser solidification (DLMS). 316L stainless steel production was used for the investigation. 

108 - A Comparison and Evaluation of Defect Detection Capabilities of Resonant Acoustic Method Non-Destructive Testing on Additive Manufactured Parts
Bryan Butsch, The Modal Shop, Inc.

Additive manufacturing enables the fabrication of complex structures that are of particular interest to the medical, aerospace, and automotive industries. Product integrity is critical in these applications. The nature of such complex geometries presents a challenge for quality control, particularly for detecting structural integrity and internal defects. Resonant Ultrasound Spectroscopy (RUS) is a well-known method for fast and cost-effective non-destructive testing of high volume parts or parts with complex geometries. New technological developments in RUS testing, specifically in the Resonant Acoustic Method (RAM) platform of RUS testing systems have expanded the capabilities of RAM. This study utilizes resonant acoustic method to obtain the resonant frequency spectrum of additively manufactured parts with and without varying numbers of printed defects as well as comparing the additional benefits of the increased frequency range and measurement resolution on the defect detection capabilities of RAM with additively manufactured parts.

226 - Minimizing Leakage in Thin Walled Structures Printed Through SLM
Andrew Yap, California Polytechnic State University

This research will investigate the scanning strategy for Selective Laser Melting (SLM) of thin walled structures. Printing thin walls using SLM is difficult because the part can warp or have high porosity. There will be two sample designs: one designed to initially determine optimal laser parameters and thickness, and another to run leakage tests. Both parts will be made using 316L stainless steel powder. Cross sectional microstructural analysis and leakage tests will be developed to measure the porosity and leakage rate of thin walled parts. The sample part will be built with different laser parameters. The parameters will be analyzed to determine the key factors that influence leakage of thin wall structures.


SESSION A21   Powder Attributes


060 - Effects of Powder Attributes of 25Cr7Ni Stainless Steel on the Properties of Parts Fabricated Through Laser Powder Bed Fusion
Arulselvan Arumugham Akilan, University of Louisville

A 25Cr7Ni stainless steel is characterized by a two-phase microstructure consisting of ferrite and austenite, providing high strength and corrosion resistance. Their application finds increasing interest in industries such as oil and gas industry. Metal powders used in L-PBF usually have a particle size in the range of 15 - 45 µm. However, powders with finer median particle sizes in the range of 5 - 25 µm are conventionally used in metal injection molding processes. This powder exhibits poor flowability making them unsuitable for L-PBF.  Prior research has shown powders with finer particle sizes to achieve better densification during L-PBF. However, very few studies on the fabrication of super duplex stainless steel parts through (L-PBF) with both coarse and finer pre-cursor powders exist. In this study, physical, mechanical, and corrosion properties of 25Cr7Ni stainless steel with both powder sizes processed by L-PBF were reported. The results indicated that powders with finer particle sizes offer higher densification and lower surface roughness than parts printed with coarser powder. The effect of heat treatment on the printed parts was also studied.

242 - Understanding the Relationship Between Metal Powder Surface Charging Behavior and Surface Chemistry
Camila Gutiérrez, McGill University

Powder flowability and spreadability for laser powder bed application is driven by many factors such as powder size distribution and powder morphology; in addition, the surface chemistry of the powder is also playing a significant role, as it influences particle cohesion and interactions with humidity. In this project, we have been looking at linking the particle tribocharging using the GranuCharge apparatus with the surface composition and crystal structure for various metallic systems. Different environmental conditions were tested on the powder to obtain different surface conditions. The quick proposed methodology to discern between powder quality could aid in maximising the quality of the laser powder bed processing.

142 - The Influence of Particle Size Distribution on the Flowability of Ti-6Al-4V Powders for Additive Manufacturing Processes
Mahdi Habibnejad Korayem, AP&C Advanced Powders and Coatings, Inc.

The recent development of powder characterization methods has opened opportunities to determine a variety of powder properties to be related to function in specific manufacturing processes. This however has not provided enough understanding on which characterization method would determine the flow properties for additive manufacturing processes. In this study, Ti-6Al-4V powders with six particle size distributions of 15-45 um, 15-75 um, 15-90 um, 45-75 um, 45-90 um, 45-106 um were compared with respect to their surface appearances, flowability, spreadability and packing densities by using the most conventional characterization methods including Hall, Carney, FT4 and granuetools. Measurable differences were observed primarily in the above characteristics indicating the differences in the additive manufacturing processability of the powders. Moreover Ti-6Al-4V powders with various particle size distribution were characterized to collect a big data such as basic flowability, compressibility, aeration response, shear, dynamic repose angle and cohesion indices. The results were used to rank the powder flowability by means of creating a scorecard analysis to identify the interrelationship amongst the characteristics and propose what feature are the most influential properties on the powders flowability. Besides, a methodology based on computer vision, machine learning, and artificial intelligence are proposed to classify the characteristics of powders having highest flowability. 


Tungsten Abstracts



SESSION T07   Powder Production


021-R - 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. 

028 - Failure Analysis of Heat Resistant Pusher Furnace Tubes Used for Tungsten Powder Production
Shankar Venkataraman, Schmidt + Clemens GmbH + Co. KG

Solid state reduction of tungsten metal oxide to metal by hydrogen is conventionally carried out using multitube pusher type and rotary furnaces. Typical reduction temperatures range from 600 °C to 1100 °C and thereby necessitate the usage of heat resistant alloys as materials of construction for the pusher tubes and rotary tubes.  Centrifugally cast nickel based alloys have been successfully used for such components and are characterized by superior elevated temperature mechanical strength and hot corrosion resistance relative to wrought counterparts.  Carbides in the austenitic matrix are responsible for the strength whereas the surface protection is provided by chromium oxide. Long term exposure to high temperatures causes microstructural changes which can impact the functional properties and thereby the integrity of the component. This contribution details a failure analysis investigation on ex-service pusher tubes which shows a circumferential crack. Microstructural characterization using optical microscopy and scanning electron microscopy are performed to understand the changes in the microstructure. The failure of the tube is attributed to localized overheating.  

192-R - Plastic Behavior and the Structure of Dislocations in Single Crystal Tungsten
Brady Butler, DEVCOM Army Research Laboratory

The deformation behavior of tungsten has been studied extensively in the past century in order to overcome issues with brittle fracture at low temperatures.  While the plastic behavior of tungsten is inherently linked to the mobility of individual dislocations, the collective motion of dislocations has strong implications for plasticity and the ultimate failure mechanisms observed at low temperatures. This study provides a detailed analysis of dislocation motion and deformation mechanisms observed in tungsten single crystals. Correlative microscopy techniques are utilized to explain strong differences in the deformation behavior of tungsten single crystals as a function of orientation. Electron backscatter diffraction and transmission electron microscopy are used to study the dislocation structure through the use of orientation imaging techniques. These results are compared with conventional dislocation imaging techniques to identify relationships between the development of microscopic dislocation structure and the resulting macroscopic deformation behavior. This work reinforces and expands our understanding of the collective role of dislocations in accommodating strain at low temperatures. 

Special Interest Program Abstracts



SIP 2-4   Alan Lawley Memorial Symposium IV: Alloying


574 - Heat Treatment of Sintered Steels: Advances in Alloying Techniques and Systems
Herbert Danninger, FAPMI, Technische University Wien

Highly loaded ferrous PM components have to be heat treated in many cases to withstand the conditions in service. Standard thermal or thermochemical treatments can be applied to PM parts but have to be adapted to the specific conditions, which includes on one hand the porosity, esp. open one, and on the other hand the alloying techniques and resulting microstructures which are more numerous and also more complex than those known from ingot metallurgy. In addition to blended elemental, diffusion bonded and prealloyed variants, also the masteralloy technique has attracted increasing interest in the last years, in particular for introducing alloy elements with high oxygen affinity such as Cr, Mn and Si. Progress has been enhanced on one hand by advanced atomizing techniques, on the other hand by software tools that enable tailoring the melting behaviour such as to establish desired homogenization processes during sintering and resulting heat treatment response.

558 - Sinter-Hardening of PM and AM Parts
W. Brian James, FAPMI, PMtech

Sinter-hardening has proven to be a process with a number of advantages for the production of cost effective  PM parts with good high mechanical properties. The response of parts to sinter-hardening depends on a number of factors including powder composition, alloying method, sintering parameters, density etc.This presentation will review some of the advantages of sinter-hardening and the influence of the important factors to consider to achieve high quality and consistent parts. The significant contribution of professor Alan Lawley to the field will also be presented.  Processes integrating 3D printing and sinter-hardening will also be discussed.

571 - Development of a Free-Sintering-Low-Alloy (FSLA) Steel for the Binder Jet Process
Christopher T. Schade, Hoeganaes Corporation

Alan Lawley’s research in powder metallurgy covered a wide range of topics from atomizing to mechanical properties. Most noteworthy of his efforts was his work in alloy development. Professor Lawley was a strong believer in the relationship between microstructure, processing and properties as it relates to the performance of the material. As new PM processes (such as additive manufacturing) were developed, Professor Lawley helped design new alloys to take advantage of the relationship between the microstructure and the processing.  This paper builds on his work in dual-phase steels to develop an alloy for Additive Manufacturing; specifically, for the binder jet process.  This work describes a dual phase low alloy steel designed so that it exhibits enhanced diffusion at the sintering temperature leading to high densities. The alloy constituents are formulated, so that upon cooling from the sintering temperature, the transformation products allow the alloy to reach the required mechanical properties.  In addition, the microstructure of the alloy can be varied post-sintering, by heat treatment, to give a wide range of mechanical properties that are suitable for automotive components. This alloy, called FSLA (free-sintering low-alloy), was designed and implemented based on the previous work in conjunction with Professor Lawley and demonstrates his continued impact on the PM community.



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