PowderMet          AMPM          Special Interest          TNT Presentations

089 - Additively Manufactured Light-Weight Refractory High Entropy Alloys for Structural Applications Above 1,200 °C
Saket Thapliyal, Oak Ridge National Laboratory

Nb alloys are excellent candidates for ultra-high temperature applications. Considering the high thermodynamic stability and multiple hierarchical deformation mechanisms offered by high entropy alloys, leveraging the ‘high-entropy’ concept in Nb-rich alloys provides a pathway for designing synergistically strong and lightweight ultra-high temperature alloys. However, the processing of these novel class of alloys remains challenging due to their high tendency to undergo impurity-induced embrittlement. Even though additive manufacturing (AM) provides an encouraging pathway for fabricating geometrically complex components, realizing crack-free fusion AM processing of refractory high entropy alloys (R-HEAs) is significantly challenging. In this work, we report the fusion AM processability, solidification behavior, and mechanical behavior of Nb alloys, including a Nb-rich R-HEA. Considerations in fabricating crack-free components with fusion AM are discussed. Current limitations in powder feedstock fabrication are highlighted and correlated with fusion AM processability, microstructural evolution, and mechanical behavior. The mechanistic details of impurity-induced embrittlement are revealed using detailed microstructural analysis of failed specimens. The chemistry-processing-structure-properties relationships as discussed in this work will enable design of scalable and high-strength Nb-rich R-HEAs.

086 - Effect of Rare Earth Solid Solution Additives on the Microstructure and Properties of Sialons
Abhijilt Roy, Kennametal Inc.

Silicon aluminum oxynitride (Sialons) based tools are mostly commonly used for high-speed-machining of heat-resistant-superalloys due to suitable mechanical, tribological, and chemical properties. However, localized high compressive stress and temperature near cutting edge causes microchipping/cracks/fracture which led to rapid tool failure. The adjustment of hardness, toughness and robust chemical-mechanical stability by controlling the microstructure, amount and chemistry of crystalline and intergranular glassy phases is necessary to overcome these shortcomings. This work investigates the impact of individual rare earth oxides and their perovskite solid solution, LaRE2O3 (RE=La, Yb, Y, Er), as sintering additives on the grain growth and mechanical properties of the Sialons. The results indicate that the use of LaRE2O3 additives causes distribution of various REs in the beta-/alpha-sialon grains and intergranular glassy phases which lead to preferential formation of elongated grains. The TEM-EDX analysis show segregation of REs mostly in the intergranular glassy phase. The changes in the microstructure and presence of multi-cations containing intergranular glassy phase do not improve the hardness, facture toughness of the tools and show marginal improvement in the metal-cutting performance.

085 - Elevated Temperature Mechanical Properties of Additively Manufactured Refractory Metals
Christopher Ledford, Oak Ridge National Laboratory

Refractory metals exhibit desirable high melting temperatures but are challenging to process via traditional routes. Due to the ability to impose high preheat conditions, thereby mitigating against thermal stresses, electron beam melting (EBM) additive manufacturing (AM) is a promising technology for processing these materials defect-free. In this work we present recent results focusing on both process-structure and structure-property relationships for pure molybdenum and tungsten. Discussion will include implications for high temperature applications and future directions in particular alloy selection.

043 - Vacuum Sintering of Stainless Steels
Amber Tims, PMT, North American Höganäs Co.

Austenitic sintered stainless steels are an attractive material choice for applications requiring a combination of good mechanical strength and superior corrosion resistance. These materials are utilized in the automotive, aerospace, and medical industries due to their exceptional performance in demanding environments. One of the critical factors in producing high-quality sintered stainless steel components is the sintering process. For optimal performance, common practice is to sinter the components in 100% hydrogen at high temperature. However, vacuum sintering is a proven sintering method for stainless steel to improve mechanical performance while eliminating oxidation potential and atmosphere contamination in PM components for enhanced corrosion performance.

In this paper, the sintering response of austenitic 316L stainless steel was examined in a vacuum sintering furnace at high temperature to conventional high temperature sintering in a pusher furnace with hydrogen. The mechanical properties and corrosion resistance are investigated.

066 - Smart Solutions to Improve Sintering Atmosphere and Process
Liang He, Air Products and Chemicals, Inc.

The powder metallurgy industry is increasingly adopting Industry 4.0 technologies and solutions to improve production processes and product quality. Proper specification, measurement, and control of furnace atmospheres are always critical to achieving the desired metallurgical and mechanical properties. The combination of atmosphere measurements and other furnace operating parameters (e.g., furnace temperature and pressure) can provide a better view of the whole production. Thermodynamic calculations and field experiences can be integrated into the smart solution to provide process engineers more capabilities to manage and optimize production. In this article, our recent research and development work on smart solutions for the powder metallurgy industry will be presented and discussed.

030 - Densification, Distortion, and Microstructure Evolution of SS 316L Powders Hot Isostatically Pressed (HIPed) at Intermittent Temperatures and Pressures
Pavan Ajjarapu, Oak Ridge National Laboratory

Powder metallurgy - hot isostatic pressing (PM-HIP) is a dynamic thermo-mechanical manufacturing process that strives to fabricate near-net shaped parts with presumably isotropic properties. While the primary objective of PM-HIP has been to achieve fully-dense components for applications in automotive, tooling, energy, aerospace, and nuclear industries, it is quintessential to understand the mechanisms and process variables governing powder densification, can distortion, and microstructural evolution of sintered regions during the HIP cycle. To this effect, SS316L powders were subjected to various HIP cycles involving intermediate temperatures, pressures and soak times. This was followed up with systematic processing – structure analyses where microstructures at different length scales were characterized. The results from this study are expected to elucidate the influence of individual process parameters on microstructure-property correlations in HIPed parts, thereby assisting in understanding the effect of HIP cycle parameters for baseline cylindrical geometries.

053 - Microstructure and Mechanical Properties of HSLA Steels Produced by Laser Powder Bed Fusion
Kerri Horvay, Hoeganaes Corporation

High strength low alloy (HSLA) steels, particularly HY80 and HY100, are used in various naval applications due to their combination of high strength, weldability and corrosion resistance. For this study both alloys were adapted for use in the laser powder bed fusion process to expand the range of possible applications. Post processing heat treatments were used to investigate the mechanical properties achievable as well as the microstructure of components manufactured by laser powder bed fusion.

105 - Ti-6Al-4V Powder Characteristics: Impacts on LPBF Build Quality and Mechanical Properties
Ma Qian, FAPMI, Royal Melbourne Institute of Technology 

This study examines the influence of powder characteristics on the quality of Ti-6Al-4V parts fabricated using laser-based powder bed fusion of metals (PBF-LB/M). Four gas-atomized spherical Ti-6Al-4V powders were characterized for surface chemistry, morphology, particle size distribution (PSD), and rheological properties. A novel powder-bed capsule method, incorporating micro-computed tomography (μCT), was employed to quantify powder-bed layer density and establish its correlation with defects and tensile properties. The findings reveal that layer density plays a pivotal role in determining as-printed quality, with a proposed benchmark of 65% of the theoretical density. Furthermore, the study underscores the importance of tailoring PDS relative to layer thickness to improve layer density under specific powder recoating conditions.

074 - AM Powder Standards: the Need to Adopt State-of-the-Art Characterization Methods
Aurélien Neveu, Granutools

The current standards rely on well-established methods allowing to evaluate independently either the intrinsic properties of the particles (e.g., particle size distribution, morphology, chemical composition) or the macroscopic manifestation of these properties (flowability, packing dynamics). However, the results obtained are strongly dependent on the measurement configuration and conditions. Moreover, the large number of methods described in the current standards prevents from providing comprehensive and universally applicable procedures to additive manufacturing end-users. This situation highlights a need to identify the relevant parameters to be used in metal powder characterization for additive manufacturing. More specifically, a clear link between powder properties and the relation with their performance in the process is still lacking.

During the last decade, improved powder characterization techniques have been developed to tackle the limitations of the standardized protocols. These new methods allow for gathering new insights into powder properties by providing new metrics and/or more repeatable and user-independent results. It is now essential to update the standards to have a wide adoption of these improved technique in the AM community. In this presentation, we will review the current standards applicable to AM powder and present the state-of-the-art powder characterization techniques and the kind of information that can be gathered by these methods.

022 - Optimized HIP Heat Treatment Techniques for an Additively Manufactured NiCrMo Alloy
Chad Beamer, Quintus Technologies

Quintus Technologies has worked together with LAM Research to develop a novel HIP and heat treatment process often called High-Pressure Heat Treatment (HPHT) that optimizes properties for additively manufactured (AM) Hastelloy C-22®. Parts produced by L-PBF often need HIPed to full densification to improve mechanical properties, but the HIP cycles can be optimized for the specific properties in question. It was found that HPHT not only eliminates the inherent L-PBF defects but also due the quicker nature of this process compared with HIP followed by solutionizing, the resultant material did not get overaged. In fact the Quintus HPHT processed material resulted in superior mechanical and aqueous corrosion performance than the standard post process route of HIP followed by heat treatment.

Surface finishing was also of great importance to the final part thus requiring the removal of an extremely stable oxide scale following heat treatment or HIP. Quintus Technologies applied the Quintus Purus® process to the Hastelloy C-22® components during the HPHT cycle mitigating the formation of the oxide scale resulting in significant cost and time savings in the final part.

This presentation will highlight how combining HPHT and Quintus Purus® provided the desired mechanical and corrosion properties for the AM Hastelloy C-22® part designed by LAM Research. It will focus on how optimization and consolidation of post-processing techniques are enabled by the advanced HIP equipment.

051 - Cold Metal Fusion - Smooth Surfaces by Green Part Smoothening
Christian Staudigel, Headmade Materials GmbH

In metal LPBF 30-70% of the costs per parts are incurred after printing by post processing such as support removal, milling and surface smoothening. These costs can be drastically reduced in cold metal fusion by processing the green part.

The cold metal fusion (CMF) process is known for reliable serial production in metal Additive Manufacturing (AM) with high part quality. CMF combines standard powder metallurgy (PM) metal powders with its proprietary binder system to form a powdery feedstock of metal powder and plastic. That feedstock can be processed into green parts on standard plastic laser sintering systems. The subsequent debinding and sintering step lead to fully dense metal parts with properties comparable to conventional manufacturing technologies.

Due to the CMF exclusive stability of the green parts, the surface can already be post-processed as green part before sintering. Standard processes like grinding, blasting and machining can be used, which saves time and cost. In a joint development project, surface roughness of Ra of 1 µm and below can be achieved by cost-efficient post processing methods within minutes. The process is easy to implement and scalable. As the formidable component is the polymer binder, the effectiveness, duration and wear are independent of the metal component. After sintering a metal part with smooth surface is achieved by easy processing in green state.

092 - The Effect of Heat Treatment on the Microstructure of Additively Manufactured Abrasion Resistant Ni-Hard Steel Parts
Thomas Murphy, FAPMI, Hoeganaes Corporation

Ni-hard alloys are designed for use in high wear and severe abrasion applications. They are Cr-Ni-Mo hypoeutectic steels with microstructures containing a high percentage of carbides in a matrix of either martensite and retained austenite or a combination of pearlite and bainite. Due to the high hardness of these alloys, machining parts to a desired shape is difficult and usually requires grinding. This severely limits the ability to manufacture complex shapes. To potentially increase the use of these alloys into applications where part design could be more complicated, powders with Ni-hard compositions were manufactured for use with additive manufacturing (AM), specifically using metal binder jetting (BJT), to take advantage of higher resolution, layer-by-layer printing of parts. In addition to benefitting from the increase in part shape, the chemical composition of the base alloy was altered with the addition of vanadium, a ferrite stabilizer and carbide/nitride former, to create harder vanadium carbides and increase wear resistance. In this manuscript, the effects of sintering and heat treating temperatures, in addition to the times at temperatures used to control the distribution of the alloying elements and the combination of transformation products, will be examined using several metallography techniques. Among the characteristics to be measured will be the size, volume fraction, and distribution of the carbides, chemical composition of the matrix and carbides, spatial distribution of the various transformation products, microindentation hardness of the individual transformation products and carbides, and others.

501 - Principles of PM Machining and the Ways to Improve
Bo Hu, North American Höganäs Co.

PM machining is a common secondary operation for components after sintering to achieve required surface finish, make dimensional adjustments or add features that could not be achieved during compaction. It is important to understand the basic machining principles and link them to the actual machining of components. The machinability of a PM component is determined by its material composition and the manufacturing route. Depending on the material composition and manufacturing route, different microstructures and hardness can be achieved. For a given PM component, selecting a suitable tool based on the machining operation is important. The machining parameters also require optimization, i.e. find the ‘sweet spot’ to achieve maximum tool life and productivity. This presentation will examine the machinability of common PM materials manufactured from different material system and processing routes; discuss the effect of base iron, alloying elements, carbon levels and density (porosity) on machining, and reviewed machining solutions commonly used to improve PM machining.

502 - Machining Responses of PM Materials Under Various Conditions
Bo Hu, North American Höganäs Co.

Machining is a complex tribological process with many factors that can influence the machinability of PM components. For a given sintered material, the microstructure and matrix hardness are the two key factors which influence machinability. Therefore, small changes in material system and manufacturing routes can cause very different machining responses, resulting in inconsistent machining and unpredictable tool failure. In addition, the type of machining operations, the tools used and the cutting parameters determine the tool life and productivity. Machinability enhancing additives are a commonly used solution to improve machining. However, to utilize the benefits provided by the additives for specific or multiple machining operations is challenging due to the complexity of machining. Therefore, developing an effective laboratory testing procedure is critical to avoid failures in production trials when introducing a machining enhancer into the material. This presentation discussed the typical features of PM machining and the common machining operations applied on PM components; examined the machining responses of different PM materials under different cutting conditions. For assessment of commercial machining additives, the presentation discussed how to link laboratory tests to production trials in evaluating the effectiveness of an additive for specific machining operations.

503 - Case Studies and Troubleshooting in PM Machining
Bo Hu, North American Höganäs Co.

Machining of PM components involves either single or multiple operations while commonly experiencing interrupted cutting for most cases. When a component is cut in a series of machining operations, it is often struggle in one operation. It is important to understand the machining conditions and collect information about the components manufacturing process to choose a suitable machining solution such as commercial machinability enhancing additives. This presentation gives examples of machining improvement for PM components and troubleshooting PM machining.