PowderMet          AMPM          Special Interest

078 - Green Machining for Sinter-Hardened PM Materials 
Bo Hu, North American Höganäs Co.

Sinter-hardened powder metallurgy (PM) materials can provide high hardness and high strength to a similar level as heat-treated PM materials without post-sintering operations. However, the parts are generally difficult to machine after sinter hardening as the part matrix is mainly constructed of martensite. This results in low productivity and high tool cost for any additional machining. Some operations, such as drilling and interrupted cutting, are impossible after sinter hardening due to the matrix hardness.  Green machining is a process to cut green parts after compaction but prior to sintering. Therefore, enabling green machining for sinter-hardened materials becomes an attractive machining solution to add features into the part which are not possible through compaction. The machining is easy to perform in this state with common cutting tools as the strength of part is mainly contributed by particle deformation and interlocks of the powder. However, there is risk of cracks and damage during part handling and machining as the green parts have far lower strength than sintered parts. With the assistance of an advanced lubricant system, green machining for sinter-hardened materials was examined for feasibility in typical PM machining such as drilling and turning. Common sinter-hardenable material systems, FL-5305 and FLC-4908, were chosen to demonstrate the capability of this green machining solution to add features (holes and grooves) on as-compacted (green) parts. 

016 - Manufacturing Copper Steel Components with Consistent Machining Performances
Cody Kalinoski, FAPMI, Engineered Sintered Components

The powder metallurgy (PM) industry continues to experience increased growth in the area of machining due to complex designs required for PM parts. The PM manufacturing process inherently allows for a wide range of alloys and additives that yield desired mechanical properties and help improve machinability. One of the most important alloying elements in PM is carbon, which is added to PM mixes in the form of graphite. During the sintering process, carbon atoms diffuse into the iron matrix, transforming it into a sintered steel part. The diffused carbon level directly influences microstructure formation and the hardness of the matrix. The microstructure formed, as well as its hardness level, directly affect the mechanical properties and machinability of the component. Previous studies on the effect of carbon levels from 0.6% to 0.9% have found that inconsistent machining is easily occur between 0.75% and 0.80%C due to the formation of proeutectoid ferrite within the microstructure. It was confirmed with components machined at production settings that the machining of parts with 0.75%C was more stable than the parts with 0.8%C, indicating a relationship between the amount of proeutectoid ferrite in copper steel and the machinability of the component. In this study, machining consistency is further examined with a component machined at production settings to demonstrate that a consistent machining could be achieved through modifications of material compositions.

035 - Joining of Two-Piece Aluminum Metal Matrix Composite (AlMMC) Transmission Carrier via Friction Stir Welding
Logan Smith, GKN Sinter Metals

Composite and multi-material assemblies are integral to vehicle mass reduction. AlMMCs comprise a group of high strength, low density materials with unique, versatile properties and attributes. Powder metallurgy (PM) processing enables low-cost, high volume production of such materials for automotive applications. Further widespread adoption of AlMMC technology requires cost reductions and improved joining capability.  Friction stir welding (FSW) was investigated as an alternative to mechanical fastening for joining of lightweight, AlMMC, automotive transmission carrier assemblies. Key considerations were strength and distortion along with overall assembly time and cost. Parametric development on both lap, and butt-type configurations yielded defect-free joints, while two potential designs were validated through material testing and functional mechanical evaluation. Weld joints and microstructures were qualified through visual and metallographic analyses including scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD). 

168 - Cold Sintering of Iron Powder Metal
Linsea Foster, Penn State University

Cold sintering of powder metal is novel method for heat treatment at unconventionally low temperatures. This process requires surface modification of individual metal particles, followed by warm compaction. This surface modification typically involves either electroless deposition or acid treatment using some material (which varies depending on the application) over substrate metal particles. The combination of surface modification and warm compaction allows for transient liquid phase sintering of particle boundaries, which accelerates particle rearrangement. The result is high-density compacts with increased strength for both green phase and sintered phase samples compared to controls. The increase in green phase strength offers a means for green machining. Furthermore, a decrease in required processing temperature and green phase machining potentially allows for decreased energy and cost consumption. Lastly, oxidation treatment of cold sintered iron systems may act as a possible method for producing insulating layers over particles that is required in soft magnetic composites.

147 - Exploration of Grain Growth Evolution with a Bi-Modal Distribution of Powder-Based Alnico 
Emily Rinko, Iowa State University

Alnico, a family of rare-earth-free permanent magnet alloys, can exhibit abnormal grain growth (AGG) upon sintering in vacuum at high temperatures (1240-1250°C), but some, including Ames Laboratory’s Co-lean Alnico, only exhibit normal grain growth. Not exhibiting AGG is a barrier to reach a large-grained, <001> textured microstructure, which is known to improve magnetic properties. As our Alnico magnets are historically formed using powder-based methods, including sintering and laser additive manufacturing, particles (from prior particle boundary oxides) may lead to particle-assisted AGG (PA-AGG), likely a key mechanism leading to desired, large-grained alnico microstructures. Using the PA-AGG mechanism, we hypothesized that a bimodal distribution of Co-lean powder could help promote AGG. In this study, we test this hypothesis and sinter Co-lean Alnico at a temperature previously determined provide an adequate balance of pinning and AGG. Funded by USDOE-OTT-TCF with EERE-VTO support and by KC-NSC through Ames Lab contract no. DE-AC02-07CH11358.

110 - Additive Manufacturing as Spring of New Materials
Francisco Cruz, University of Coimbra

Selective Laser Melting (SLM) of multimaterial has been increasing. The main targets are to improve properties of the 3Dobjects resulting from SLM and to decrease secondary processing (i.e. welding). Now, SLM plays a new role in reducing standard high-cost steel by improving the low-cost steel “surface” properties. For example, in molds, only the “surface” must have properties suitable to attain high hardness/loss. Thus, low-cost steel for mold structure will be transformed into high alloy steel in the critical zones (injection) due to the addition in the last layers of chemical elements that could improve a suitable microstructure (small grain size and precipitation hardening). The addition of alloy elements with a high affinity to carbon and appropriate dimensions could be the solution. In the present study, vanadium powders (1-5 %wt.) and carbon allotropes (graphene, carbon nanotubes…) were mixed with a steel powder to guarantee an ultra-high gloss of a mold cavity. 

121 - Improving Surface Quality and Geometric Fidelity of Water Atomized Pure Iron in Laser Powder Bed Fusion
Allan David Rogalsky, MSAM—University of Waterloos

Laser powder bed fusion (LPBF) technology adoption is strongly driven by the ability to produce parts with a high degree of geometric complexity. Such components often require a threshold surface quality and geometric fidelity to avoid excessive post processing and maintain competitive advantage.  Achieving these consistently is an active area of research in the field of additive manufacturing. This study proposes a combined physics-based modeling and empirical strategy to refine water atomized pure iron surfaces in close contact with the powder bed. Using parameters such as power, effective velocity, and hatch spacing control can be exercised over heat dissipation, melt pool geometry and melt pool stitching resulting in meaningful variation in part properties.  Control of heat dissipation was important for artifact feature resolution and geometric fidelity.  Surface roughness achieved range from Ra = 24 µm on vertical surfaces to Ra = 59 µm for unsupported surfaces at 30° from horizontal.  

059 - Anisotropic Al-NdFeB Composite Permanent Magnets Built by Cold Spray Additive Manufacturing
Fabrice Bernier, National Research Council Canada

In recent years, there has been a rapidly growing interest in the fabrication of complex-shaped permanent magnets using additive manufacturing. Producing complex shape magnetic components could revolutionize the design and performance of electrical machines. Magnetic performance of permanent magnets produced by additive manufacturing is very often limited due to the use of isotropic powders. In this study, cold spray additive manufacturing was investigated for producing Al-NdFeB composite permanent magnets using anisotropic NdFeB powders. The effect of various process parameters (powder mixes composition, temperature, substrate composition, deposition angle, etc.) on the composites deposition efficiency and magnetic anisotropy was evaluated. Magnetic characterization (remanence, coercivity and BHmax) was carried out in three orthogonal directions to quantify the level of anisotropy. Image analysis of the as-received NdFeB powders morphology as well as of sprayed samples was performed and the microstructure and particles spatial orientation was correlated to the observed magnetic anisotropy. Finally, performance of anisotropic magnets built using optimal cold spray additive manufacturing parameters was compared to that of magnets built with isotropic powder. 

042 - Role of Composition in High Temperature Heat-Treatment Response of Additively Manufactured 17-4 PH Stainless Steel
Todd Palmer, Center for Innovative Sintered Products

Precipitation hardening (PH) stainless steels processed using additive manufacturing (AM) display variations in heat treatment responses and mechanical properties.  These variations have been primarily attributed to changes in interstitial element compositions within the allowable ranges. With AM processing of these alloys, composition variations of both interstitial and primary alloying elements combined with microstructures that differ from wrought, impact the thermodynamic stability of important phases such as copper, austenite, delta-ferrite, nitrides, and oxides. This work aims to connect compositional changes in interstitial alloying elements like nitrogen and oxygen as well as other primary elements in AM PH stainless steels to microstructures after hot isostatic pressing (HIP) and solution heat-treatments. A predictable, high temperature heat-treatment response can be established by investigating key aspects of solutionizing and HIP such as the thermodynamic stability of delta-ferrite and copper as well as the influence high temperature phases like nitrides and oxides.

025-R - Impact of Particle Size on Rheology and Mass Flow During  Directed Energy Deposition Additive Manufacturing
Todd Palmer, Center for Innovative Sintered Products

Significant variations in mass flow rates during processing were identified for a lean (UNS S32101), standard (UNS S32205), and super (UNS S32750) duplex stainless steel powders using directed energy deposition additive manufacturing. Across three different directed energy deposition systems, the lean grade consistently displayed the lowest mass flow rates which impacted final build geometry.  Although traditional powder characterization methods were unable to identify differences between the three powders, advanced powder and rheological characterization tools linked particle characteristics and rheological properties to powder flow and performance. The lean grade was discovered to have a particle size distribution shifted to slightly larger sizes, which resulted in a higher fraction of larger particles with higher masses that resisted motion and increased particle-particle and particle-gas flow resistance. This increased flow resistance was captured through cohesion strength and fluidization measurements during rheological testing. 

091-R - Boron Modified Silica Nano-Lubricant as a Powder Rheology Modifier and Sintering Aid for AISI 420
Arun Chattopadhyay, Uniformity Labs

The use of nanolubricants in powder metallurgy is a major advancement for various additive manufacturing processes. The use of nanoadditives in the form of nanoparticles is highly efficient due to their high surface area and ability to adhere specifically on metal particles smaller than 10 micron. This study is aimed to investigate the effect of adding boron-modified SiO2 nano-powder on the sintering properties of AISI 420 stainless steel (SS). The final density, dimensional changes, and mechanical properties have been studied for the samples prepared under a series of sintering conditions.

071 - Tantalum and Niobium Powders for Cold Spray Applications
Matthew Osborne, Global Advanced Metals

Tantalum and niobium are well known for their resistance to high temperature and corrosive attack making them ideal for applications beyond the capability of more mainstream metals. Their high ore and processing costs, however, often prohibit their use in bulk form for reactor walls, piping, and similar structures. Fortunately, the increasing development and application of cold spray is expanding opportunities to use Ta and Nb as surface coatings, thus offering resistant surfaces at lower cost. Among the application areas include chemical processing, medical implants, and nuclear energy.  The tantalum and niobium powders for cold spray testing and development were produced from electron beam melted ingots with overall purities of greater than 99.99%. Powder was tested for sprayability and deposition efficiency. Results show highly dense deposits when powder was cold sprayed using helium carrier gas. Triple lug shear strength and microhardness of the deposits indicated a mechanically robust coating was achieved.

104 - The Production of Tungsten Rhenium Alloys with Varying Rhenium Content
Scott Ohm, H. C. Starck Solutions

Tungsten rhenium alloys are high temperature solid solution refractory metal alloys used in a variety of aerospace and energy applications.  Pure tungsten has low temperature brittleness and a high ductile to brittle transition temperature, leading to cracking issues in Additive processes.  Low levels of rhenium are known to improve ductility and lower the susceptibility to cracking.  In this presentation, spray drying and plasma spheroidization methods are used to produce both fine powders for Powder Bed Laser Fusion (PBLF) applications, as well as coarse powders for Directed Energy Deposition (DED).  The flexibility of the process allows for infinitely customizable alloy compositions with a full range of particle size control.  Rhenium levels of 1 to 7 weight percent were produced with an investigation of particle size distribution, density, flow rate, and chemical analysis.

034-R - Moisture in Metal Powders: How to Track Properties Drift During Storage?
Aurélien Neveu, Granutools

Metal powders feedstock is an important part of powder bed based Additive Manufacturing (AM) processes. The quality of the build parts is highly dependent on the powder bed homogeneity and density which are directly related to the powder properties. However, feedstock batch properties can evolve due to powder production variability, storage, aging or successive recycling. Especially, moisture can induce oxidation that leads to an alteration of the chemical properties of the particles and subsequent modification of particle/particle interactions. A better understanding of the influence of moisture on metal powder behavior is thus essential to reduce feedstock variabilities due to property drift during storage. In this study, the influence of short and long-term exposure to humid air on several metal powders is investigated. In order to track small variations of powder properties, an improved tapped density analyzer is used to provide high accuracy and repeatability of the measurements.

230 - The Effect of Co on Magnetic Properties of MnPt Alloy: A Computational Study
Hasani Chauke, Materials Modelling Centre, University of Limpopo

Abstract. MnPt has attracted a lot of attention in the practical applications such as spintronics due to its high stability with very high Nel temperatures. Previously, it was reported experimentally that L10 MnPt alloy shows magnetic ordering with no magnetic moment. In this study, the effects of partial substitution of Mn with Co on magnetic properties is being investigated using density functional theory. The thermodynamic, magnetic and mechanical properties were determined to check the stability of Pt50Mn50-xMx alloys (x=6.25, 12.5, 18.75, 25) alloys. The calculated lattice constants and heats of formation of Mn50Pt50 agree well with available experimental results. It was found that both B2 and L10 Pt50Mn50-xCox (x=6.25, 12.50) are thermodynamically stable due to the negative heats of formation. In Pt50Mn50-xCox (x=18.75, 25), only the L10 phase was found to be thermodynamically stable while B2 phase is unstable. The results of the Bain path transformation investigation showed that the L10 phase has lowest heats of formation when the c/a ratio is 1.20 for 6.25 at. % Co. Our calculations indicated that a ferromagnetic state can be achieved in Pt50Mn50-xCox by a small variation in the tetragonality ratio from 1.1 to 1.3. Furthermore, the ductility of Pt50Mn50-xCox is predicted using Pugh‘s ratio, Poisson‘s ratio and Cauchy pressure. This work showed that density functional theory can be exploited to propose new possible composition for future magnets in spintronics application.

514 - Integrated Computational Materials Engineering for the Optimization and Design of Advanced Materials Suitable for Powder Processing
Jeffrey Grabowski, QuesTek Innovations LLC

QuesTek Innovations LLC has been employing Integrated Computational Materials Engineering (ICME) technologies to the optimization, design and development of advanced materials for nearly 25 years. While most if its commercial success has been in wrought/forged bar or cast manufacturing methods, QuesTek has also been very active in using ICME across a range of alloy systems of interest to the powder metallurgy community.

This talk will give an overview of QuesTek’s approach to ICME and several case studies of applying ICME to powder processed material, including for example the design of novel metal matrix composites processed via HIP and Spark Plasma Sintering for high temperature friction stir welding tools, an ICME-based modeling tool for HIPing for tailoring microstructures to achieve improved fatigue life, and a number of projects applying ICME to developing advanced Nb, W and other alloys tailored for additive manufacturing.

An outlook of future opportunities for ICME in the powder industry will also be presented.

502 - An Integrated Computational Materials Engineering Approach for Design of Aluminum Alloys for Laser Powder Bed Additive Manufacturing
Rajiv Mishra, University of North Texas

Laser powder bed fusion (LPBF) additive manufacturing (AM) technologies have emerged as leading choice for complex components. The opportunities of significant weight saving through component design can be coupled with choice of lightweight aluminum alloys. Significant literature is available on modified and new aluminum alloys for LPBF-AM. A conventional approach has been to use alloy compositions that are good for casting or fusion welding. Integrated computational materials engineering (ICME) provides a better framework for new composition development or modification of existing alloy for LPBF-AM. In this short overview, an ICME approach for new alloy development, specifically for LPBF-AM aluminum alloys, will be highlighted. The alloy chemistry can be tailored to control microstructural evolution during solidification and enhance printability. New aluminum alloys provide opportunities for high structural efficiency in as printed parts using the ICME approach for printability-performance synergy.