PowderMet          AMPM          Special Interest

024 - Investigation of Corrosion Performance of Standard PM Stainless Steels with Secondary Processing for Enhanced Corrosion Protection
Daniel Stauffer, Penn State University DuBois

Corrosion is a concern impacting any iron-based material. According to the National Association of Corrosion Engineers, global costs due to corrosion are estimated to be > $2.5 trillion USD annually.  To combat this, stainless steel materials or specialized coatings and plating are selected for environments where standard iron-based materials would corrode and degrade.  Powder metallurgy is no exception, where great care is taken for materials selection and process control to optimize corrosion protection.  In this paper, corrosion testing of powder metallurgy austenitic and ferritic stainless-steel material was conducted in regard to ASTM test conditions to investigate the impact of secondary process operations on corrosion performance.  Baseline results for standard powder metallurgy materials is presented and visually used as a comparison to determine a factor of performance for the secondary operations evaluated.  Radial crush strength and apparent hardness as well as microstructure measurements were also performed to investigate the impact of processing on mechanical properties of the modified stainless steel materials.    

103 - Stabilizing Steam Treatment Process for Consistent Results of PM Parts Oxidation
Ravindra Kumar Malhotra, Malhotra Engineers

Steam treatment is an important post sintering operation in a powder metallurgy (PM) plant. The technical requirements of oxide coating will vary as per end use of the oxidized parts. It is important to keep the steam oxidation or bluing process well controlled to not only give uniform blue appearance but also expected metallurgical results like oxide depth and uniform surface hardness of PM parts being processed. This requirement does not change in any of the methods employed for steam treatment process. It can be with a boiler or a boilerless steam treatment operation. Whether wet nitrogen is used or any other method like a combined sintering and steam treatment operation, what leads to a stable process of oxidation day in day out despite short comings of methods of steam production deployed needs to be understood to meet process optimization. It will need a relook at oil removal methods as well as steam section heating methods along with handling of process by products like hydrogen gas and foreign carrier gas like nitrogen. Understanding of steam oxidation method deployed and limitations of steam source will help in a stable process control for best uniform color, hardness, depth of oxide and sealing results. 

221 - Mechanical Properties and Porosity Analysis of Low Allow Ni Mo PM Steel Under Hot Isostatic Pressing Coupled with Double Press Double Sinter
Nicolette Brossard, Penn State University DuBois

The purpose of this research is to investigate microstructural mechanisms operative under isostatic pressing and proprietary heat treatments that can help achieve near wrought density and improved mechanical properties of a low alloy nickel molly steel powdered metal processed by micro-Ingot double press double sinter (MI-DPDS) route. Specifically, porosity, density, fatigue life, transverse rupture strength and hardness are evaluated and compared. Cross sectional porosity mapping of sintered compacts conducted using scanning electron microscopy show regions close to the edges of the sample had low porosity while the center region had relatively higher porosity in MI-DPDS. With higher density, mechanical properties of the material are improved. We attempt to analyze, quantify and report underlying microstructure property relationships and the size evolutions of the porosity throughout the sample under different processing conditions that affectively enable the sample to reach close to wrought density as well as increase its mechanical properties.

119 - Properties and Applications for Iron Powder Made by Gas Atomization
Kalathur Narasimhan, FAPMI, P2P Technologies

Applications and properties of iron powder made by inert gas atomization are reviewed.  Iron powders are used in many different applications such as: soft magnetics; catalysts; water remediation; ink and toner carriers; coatings such as magnetic paints; welding; food grade iron for iron fortification; additives to dyes and stains.  The gas atomization of pure iron is sometimes difficult due to the reaction of the iron with the refractories used in the introduction of the molten metal to the atomizing jet. The current process overcomes this limitation and the gas atomized iron powders in this study are reviewed in comparison to electrolytic iron in terms of particle size, shape, grain size and porosity levels. Applications of the iron, particularly, in terms of magnetic properties and use in 3D printing are also reviewed.

046 - Fatigue Properties Investigation of Low Alloy Steel “Micro Ingot” based Hi-Density + Hipped TRS Bars
Harb Nayar, FAPMI, TAT Technologies LLC

Through collaboration with multiple partners, this study investigates transverse rupture strength and fatigue properties of low alloy steel TRS bars produced by new DPDS route to 7.3+ g/cc density combined with HIP starting with un-annealed as water atomized low allow “Micro Ingots” powder. Earlier investigation shows that mechanical properties like fatigue strength are significantly improved under the following 2 finished TRS bar conditions, DPDS TRS bars to 7.3-7.4 g/cc & DPDS + HIP TRS bars to 7.7 g/cc.  Plan for the more detailed near future investigation will be shared to further improve the mechanical properties of low alloy steel high density PM parts.

127 - Attempts in Improving Corrosion Behavior of a Powder Metallurgy Steel Processed to Wrought Densities
Harb Nayar, FAPMI, TAT Technologies LLC

Powder metallurgy steels have limited corrosion life, due to higher surface area and diffusion induced chemical heterogeneity at elemental powder interfaces. We investigate a route to enhancing corrosion resistance using a modified Double Press Double Sinter process utilizing pre-alloyed powders (we call micro ingots). Subsequent HIP compaction of DPDS parts is utilized to achieve densities analogous to wrought metal. We compare the corrosion behavior of a popular powder metallurgy steel both before and after hot isostatic press with wrought steel of similar composition, using immersion corrosion tests and potentiodynamic polarization testing conducted under service environments. The study analyzes the microstructure using metallography, chemistry with Electron dispersive analytical X-ray and surface stress state using Xray diffraction, and proposes their relations with passivation behavior, corrosion potential and operative corrosion mechanisms.

022 - Advancements in High Pressure Heat Treatment (Combining HIP and Heat Treatment) for AM Parts
Chad Beamer, Quintus Technologies

The use of HIP is of growing interest for AM parts with significant research efforts in place to mature and optimize these systems.  Historically HIP has been used to eliminate internal cracks, voids, and pores with subsequent heat treatment performed using conventional technologies to obtain the desired microstructure and mechanical performance.  Recently it has been shown in literature and practice that it is possible to integrate HIP and heat treatments in the HIP furnace with the aid of high-pressure gas cooling or quenching, an approach known as High Pressure Heat Treatment(HPHT).  One recent development advancing the HPHT technology is steered cooling.  Steered cooling enables the HIP system to now cool based on component temperature at a predefined rate for targeting desired material properties.  This presentation will cover the most recent HPHT advancements and learnings and review HPHT cast studies performed on AM alloys highlighting both material performance and productivity improvement.  

154 - An Analysis of Different Finishing Techniques for Surface Roughness Improvement of AM Components 
Jyrrl Figueroa, 3DEO, Inc.

The surface roughness of metal components is a deciding factor in whether a component can consistently meet designed geometries and tolerances.  In addition, it can impact a wide range of properties such as wear resistance, fatigue life, and plating adhesion.  This paper presents an evaluation of different finishing techniques for improving the surface roughness characteristics of metal components produced by Intelligent Layering.    
Intelligent Layering is a novel binder-assisted, sintering-based technology best defined as a process with additive and subtractive elements. The process is suitable for high-volume metal production.  Test parts were printed, sintered, and then split to be processed using different finishing methods including mechanical, chemical, and electropolishing techniques. The change in the surface roughness after each finishing process was quantified and compared.

164 - Amorphous-Crystalline Nanostructural Nd-Fe-B Permanent Magnets Using Laser Powder Bed Fusion: Metallurgy and Magnetic Properties
Julan Wu, University of Nottingham

Although certain physical properties are required for the L-PBF candidate materials, the strength of AM to process net-shape material to reduce the material waste and offer higher design freedom for the applications attracted interests to process functional materials. Laser powder-bed fusion (L-PBF) additive manufacturing (AM) has attracted wide interest for the production of Nd-Fe-B permanent magnets, benefitting from minimising the mineral waste of the rare-earth elements and post-process procedures. Most studies on L-PBF Nd-Fe-B focused on reducing defects in the printed parts and the resultant magnetic properties. Detailed analysis of the microstructure that results in the permanent magnetic properties is yet to be published. In this research, a combination of high-resolution microstructural investigations was conducted for this purpose. For the first time, an in-depth analysis of the grain structure in terms of the morphology, size distribution, and texture is presented and correlated to the permanent magnetic performance. The mechanism of the phase formation, the nanocrystalline microstructure and the process-structure-property relationship is presented in this paper. Despite the method of parameter optimisation to enhance the magnetic properties, tailoring the feedstock powder for L-PBF and the upgradation on the L-PBF system to produce anisotropic Nd-Fe-B material can be the themes for the future development of L-PBF.  Since the research interest of this study is on the permanent magnetic Nd-Fe-B alloy using L-PBF, the challenges facing the Nd-Fe-B alloy are to be highlighted. The process-structure-property relationship is clarified in this research and the guidelines for the future development of this topic is to be proposed.

115 - Metal 3D Printing of Large Components Using DMD Technology
Farhad Ghadamli, DM3D Technology

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.  

157 - Hybrid Manufacturing Approaches for the Production and Repair of Industrial Tooling
Tom Feldhausen, Oak Ridge National Laboratory

Hybrid manufacturing systems interleave both additive manufacturing (AM) and conventional subtractive machining (CM) processes within the same work volume, which allows build material to be deposited and machined in a single step. Building upon the recent advancements in the hybrid manufacturing industry, the ORNL team has been developing approaches to rapidly repair common failure mechanisms in production tooling. Current industrial practices for tooling repair are largely manual, require highly skilled workers and are prone to the formation of brittle material phases that result in poor performance and high residual stresses. With a concentration on material interfaces between AM depositions and the exiting tool surfaces, the team has developed and characterized appropriate compatible materials with high hardness. Using embedded sensing and data analytics tools, in-situ state information can be captured, including thermal history, weld pool monitoring, machine telemetry, and topology. Using this rich data stream, qualification and certification approaches have been investigated to enable rapid repair and modification of existing tools with minimal downtime and loss of production capacity. According to a Case Western University study on tooling rejuvenation and repurposing, industry-wide gains in die casting from extended life alone could be more than $500M, with similar gains among other fabrication processes. In addition to extended life, the hybrid manufacturing approach to tool and die repurposing also offers the potential to shorten the design/manufacturing cycle by compressing tooling lead times

045 - Profilometry Based Indentation Plastometry Applied to Binder Jet Additively Manufactured Parts
Jimmy Campbell, Plastometrex

'Profilometry-based indentation plastometry (PIP) can be used to determine the stress-strain characteristics of metallic materials from indentation testing of a small, localized area. It is currently very well suited for testing on isotropic, fully-dense and homogeneous materials. The procedure uses the residual indent profile and an (accelerated) iterative FEM simulation of the indentation process. The plasticity parameters in a constitutive law (within an indentation finite element model) are repeatedly changed until optimum agreement between measured and predicted residual profile shapes is obtained. The technique characterises the full uniaxial stress-strain relationship, including the yield stress and ultimate tensile strength. Binder jet 3D printed parts in the as-sintered state can have residual porosity in the range of 0.5 - 2 %. This has an effect on uniaxial tests (tension and compression) as well as on PIP. The effect of porosity on the outcomes of these different mechanical tests, and the prediction of tensile test data from PIP on materials with a small amount of porosity is explored in this study.

120 - An Analysis of Precision and Material Properties of Parts Produced via Intelligent Layering, Additive Manufacturing Process
Midhun Gopakumar, 3DEO, Inc.

Intelligent layering is best defined as a process with additive and subtractive elements. An even layer of 17-4 PH metal powder is spread on the build plate, a binder is applied, subsequently the binder is cured through a heat pass. The part geometries are pocketed or face milled using a precision micro-end mill in a layer by layer fashion. The parts are printed in the green state, depowdered and then sintered to achieve high density final products. This study aims to statistically analyze the precision and accuracies of parts produced by the Intelligent layering process and discusses relevant factors that affect it. The study also looks at the density and hardness distributions of as-sintered parts as a function of its location within the build.

150 - Assessment of Particle Size and Shape for Bound Metal Powders Using Digital Image Analysis
Brady Butler, U.S. Army Research Laboratory

The accurate measurement of particle size and shape distributions are critical to many powder metallurgical processes.  These metrics have a strong influence on powder flowability, packing, and compressibility, in addition to many other factors that affect densification behavior and the overall performance of sintered components.  The particle size of loose powders is easily measured using a variety of standard techniques (e.g., laser diffraction and sieve analysis).  However, these approaches cannot quantify size distributions in bound particulates, which are commonly used for powder injection molding or material extrusion additive manufacturing. This study discusses the efficacy of image-based techniques for assessing the particle size of bound metal powders.  Improvements in image acquisition and analysis can help to improve particle sampling and create a reliable assessment of particle size distributions. However, there are still significant challenges in accurately assessing the size and shape of three-dimensional particles with two-dimensional image-based techniques.  

038 - An Integrated Computational Materials Engineering Approach to the Design of ODS Alloys for AM
Ida Berglund, QuesTek Europe AB

Integrated Computational Materials Engineering (ICME) technologies are becoming increasingly popular for the design and development of new alloys. ICME-based design creates a more sustainable path to materials development, reducing development time and costs compared with traditional trial-and-error based approaches. Aiming to increase operation temperatures within the processing industry, leading to better energy efficiency, oxide-dispersoid strengthened (ODS) alloys manufactured via AM present a promising opportunity for novel components (e.g., gas burner heads). This presentation emphasizes the use of ICME models and tools for the accelerated development of novel ODS alloys, highlighting the key Process-Structure-Process-Performance relationships and integration steps in a ICME framework allowing for tailored design solutions for AM.

516 - Understanding the Physical Response of Stabilized Nanocrystalline Alloys Through Integrated Computational Material Engineering
Kris A. Darling, U.S. Army Research Laboratory

Unlike conventional nanocrystalline (NC) alloys, the family of thermo-mechanically stabilized alloys have proven divergent mechanical response.  In many cases this has resulted in first of a kind observations and unpredicted physical properties, such as extreme prolonged high temperature exposure, creep resistance and suppressed phonon drag.  That is, they drastically depart from the unusual behavior and well-established norms of traditional bulk nanocrystalline alloys.  Such significant deviations provides a new frontier for fundamental discovery.  The talk will review the computational materials science efforts utilized in overcoming uncertainty in the knowledge of how these materials defy traditional wisdom, where experiments were lacking. 

156 - Comprehensive Design for Part Deformation in Metal Binder Jet Additive Manufacturing
Yousub Lee, Oak Ridge National Laboratory

Anisotropic part deformation is a challenging issue in metal binder jetting additive manufacturing. It is considerably difficult to know magnitude of shrinkage rate under non-isotropic sintering environment in priori. It is because the shrinkage is dependent on particle material properties, various process parameters, complex part geometries, particle size distribution, and associated change of relative density. To improve a prediction ability in binder jetting technology, three tasks should be carried out. First, a precise prediction of initial relative density and spatial distribution for a selected geometry. Second, validated constitutive relationships to describe various parameters and geometry response to part shrinkage and distortion. Third, development of efficient method for accurate prediction of shrinkage and distortion in part-scale. In this presentation, an integrated simulation method has used to investigate powder spreading kinetics, binder effect, and part shrinkage for in-depth understanding on the part deformation.