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DOE OSTI2024

Binder systems and methods for tape casting lithium garnet electrolytes

Slurry compositions, tape casting binder systems and fabrication methods for the fabrication of lithium-garnet electrolyte scaffolds for use in solid state batteries and other devices are provided. Slurry compositions may be optimized mixtures of LLZO powder, a dispersant, a lithium salt, a wetting agent a binder, a plasticizer and at least one solvent. The optimized ceramic slurry compositions may include MgO as a sintering additive to improve density and ionic conductivity of the doped-LLZO sheets and produce a fine-grained microstructure. Sintering protocols for cast slurries of commercially available doped LLZO powders eliminate the requirement of mother-powder coverings or externally applied pressure. An environmentally friendly water-based system using methylcellulose as a binder is also provided producing green tape and final properties comparable to those obtained with organic solvent-based systems.

Jonson, Robert↗

DOE OSTI2024

Systems and methods for automated depowdering and transfer of additively manufactured objects

Systems and methods for additive manufacturing of objects are disclosed. The system includes an object builder subsystem configured to additively manufacture an object in a powder bed, an object extraction subsystem configured to extract the object from the powder bed, and a depowdering subsystem configured to remove powder from the object while the object is gripped by the gripper assembly. The object extraction subsystem includes a gripper assembly comprising two or more gripper members that each include a perforated mesh structure.

Elliott, Amelia M.↗

DOE OSTI2024

Ultrahigh Performance Metallic Turbine Blades for Extreme Environments

In ULTIMATE Phase-I, The Boeing Company and Alloyed Inc. aimed to produce ultrahigh performance metallic extreme environment turbine blades with a base blade alloy capable of inert operation at 1300C, and a maximum coated blade operating temperature up to 1800C. High-performance structural designs for extreme service conditions place additional demands on the present material capability and can potentially outpace the current state-of-the-art in the alloy design space and metal processing. As a part of exploration and adoption of novel concepts for material maturation, the team explored a series of capable base novel refractory complex concentrated alloy (RCCA) compositions and potential powder enhancements. Advanced manufacturing processes, with a focus on laser powder bed fusion additive manufacturing (AM) and powder metallurgy (PM) approaches, were applied to consolidate new alloys and for near net shape processing of blades from the base RCCA.

Yousefiani, Ali↗

DOE OSTI2022

A review on additive manufacturing of refractory tungsten and tungsten alloys

Here we review the progress of additive manufacturing effort on refractory metal tungsten and tungsten alloys. These materials are excellent candidates for a variety of high temperature applications but extremely challenging to fabricate via additive manufacturing due to a series of existing issues during the manufacturing. We outline these issues and discuss the current understanding and progress to tackle them. Laser powder-bed-fusion, laser directed-energy-deposition, and electron beam powder-bed-fusion are three common techniques that have been applied to additively manufacture pure tungsten. This overview discusses current observations and understanding on the issues associated with each of these techniques. We identify future research opportunities in additive manufacturing of refractory metals.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Investigation of thermal damage in explosive bridgewire detonators via discrete element method simulations

Exploding bridgewire (EBW) detonators are used to rapidly and reliably initiate energetic reactions by exploding a bridgewire via Joule heating. While the mechanisms of EBW detonators have been studied extensively in nominal conditions, comparatively few studies have addressed thermally damaged detonator operability. We present a mesoscale simulation study of thermal damage in a representative EBW detonator, using discrete element method (DEM) simulations that explicitly account for individual particles in the pressed explosive powder. We use a simplified model of melting, where solid spherical particles undergo uniform shrinking, and fluid dynamics are ignored. The subsequent settling of particles results in the formation of a gap between the solid powder and the bridgewire, which we study under different conditions. In particular, particle cohesion has a significant effect on gap formation and settling behavior, where sufficiently high cohesion leads to coalescence of particles into a free-standing pellet. This behavior is qualitatively compared to experimental visualization data, and simulations are shown to capture several key changes in pellet shape. We derive a minimum and maximum limit on gap formation during melting using simple geometric arguments. In the absence of cohesion, results agree with the maximum gap size. With increasing cohesion, the gap size decreases, eventually saturating at the minimum limit. In conclusion, we present results for different combinations of interparticle cohesion and detonator orientations with respect to gravity, demonstrating the complex behavior of these systems and the potential for DEM simulations to capture a range of scenarios.

cohesive powders↗

DOE OSTI2019

Investigation of the Effect of Foaming Agent on the Fabrication of NiTi Foams Using the Self-Propagating, High-Temperature Synthesis Process

Fabrication of NiTi intermetallic foams using the self-propagating, high-temperature synthesis (SHS) process was investigated. Weighed amounts of powders taken from an equimolar mixture of Ni and Ti powders along with 0.5, 1, and 1.5 wt pct of different foaming agents were cold pressed to form cylindrical compacts 10 mm in diameter, 20 mm in height, and 7 to 8 g in weight. A novel, induction-assisted ignition method was used for indirect heating and igniting the compressed mixtures at one end. As a result of intensive exothermic reaction between Ni and Ti and decomposition of foaming agents and liberation of gases, highly porous products were obtained. Characterization of the products was carried out using X-ray diffraction (XRD) and a scanning electron microscope equipped with an energy-dispersive spectroscope (SEM-EDS). The main phase in the products was detected to be B2(NiTi) with minor amounts of NiTi{sub 2} as the secondary phase. Other undesirable phases, such as Ni{sub 4}Ti{sub 3} and Ni{sub 3}Ti, were not detected. The effect of type and percentage of foaming agent on the formation and distribution of pores within the products was studied. Final products with porosities up to ~ 80 vol pct were obtained by adding foaming agent. Under the conditions of this study, CaH{sub 2} proved to be the most effective foaming agent considering its ability to generate a uniform distribution of pores, while TiH{sub 2} was not considered favorable due to its decomposition at relatively low temperatures. In general, the addition of foaming agents in amounts higher than 1wt pct is not recommended; due to the endothermic nature of thermal decomposition reactions of foaming agents, excessive use of these agents can result in suppression of the exothermic reaction.

36 MATERIALS SCIENCE↗

DOE OSTI2021

AFRL Additive Manufacturing Modeling Series: Challenge 1, Characterization of Residual Strain Distribution in Additively-Manufactured Metal Parts Using Energy-Dispersive Diffraction

A machine component fabricated by additive manufacturing (AM) of metal powders often possesses steep residual stress gradients with significant magnitudes due to large temperature gradients that transpire within a localized area during fabrication. These processing-induced residual stresses can cause distortion of the part, and if they are of significant magnitude, they could induce cracking of the component, degrade printability, and/or diminish subsequent mechanical performance. The ability to predict these residual stresses imparted by AM is an important step in permeating AM technology for advanced manufacturing. Calibration and validation of AM process models used for prediction are, therefore, a critical step in understanding the origin and mitigating the challenges associated with residual stresses inherent to the AM process. In the present work, the residual strain distributions in components with simple geometries fabricated by a laser powder bed fusion (LBPF) process were characterized non-destructively using energy-dispersive X-ray diffraction in support of the US Air Force Research Laboratory Additive Manufacturing Modeling Challenge Series Groeber et al. (JOM 70:441-448, 2018). The measurement setup and approach are described in detail so that the data can be used as a benchmark to calibrate and validate models for the prediction of macro-scale residual stresses due to the LPBF process.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Dissolution zone model of the oxide structure in additively manufactured dispersion-strengthened alloys

The structural evolution of oxides in dispersion-strengthened superalloys during laser-powder bed fusion is considered in detail. Alloy chemistry and process parameter effects on oxide structure are assessed through a parameter study on the model alloy Ni-20Cr, doped with varying concentrations of Y 2 O 3 and Al. Small angle neutron scattering measurements of the dispersoid size distribution show the dispersoid size increases with higher laser power, slower scan speed, and increasing Y 2 O 3 and Al content. Complementary electron microscopy measurements reveal reactions between Y 2 O 3 and Al, even in nanoscale dispersoids, and the presence of micron-scale oxide slag inclusions in select specimens. A scaling analysis of mass and momentum transport within the melt pool, presented here, establishes that diffusional structural evolution mechanisms dominate for nanoscale dispersoids, while fluid forces and advection become significant for larger slag inclusions. These findings are developed into a theory of dispersoid structural evolution, integrating quantitative models of diffusional processes – dispersoid dissolution, nucleation, growth, coarsening – with a reduced order model of time-temperature trajectories of fluid parcels within the melt pool. Calculations of the dispersoid size in single-pass melting reveal a zone in the center of the melt track in which the oxide feedstock fully dissolves. Within this zone the final Y 2 O 3 size is independent of feedstock size and determined by nucleation and growth kinetics. If the dissolution zones of adjacent melt tracks overlap sufficiently with each other to dissolve large oxides, formed during printing or present in the powder feedstock, then the dispersoid structure throughout the build volume is homogeneous and matches that from a single pass within the dissolution zone. Gaps between adjacent dissolution zones result in oxide accumulation into larger slag inclusions. Predictions of final dispersoid size and slag formation using this dissolution zone model match the present experimental data and explain process-structure linkages speculated in the open literature.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Achieving SEI preformed graphite in flow cell to mitigate initial lithium loss

The irreversible lithium loss due to the formation of solid electrolyte interphase (SEI) in the initial cycle on the graphite anode greatly reduces the overall cell energy density of lithium ion batteries, that is, the lost Li ions from forming SEI lead to the decrease of Li ions for the intercalation. The method of cathode prelithiation has been widely explored to compensate this lithium loss. However, these cathode additives with high lithium contents inevitably lower the loading of the cathode active materials. In this work, we report a novel approach to solve this challenge, a facile graphite prelithiation method by preforming SEI layers on the surface of graphite powders (Pre-SEI graphite) utilizing a specially designed flow cell. The Li accommodation in the graphite anode can be controlled by the operating time and current density in the flow cell for the electrochemical SEI formation. As a result, we demonstrate a 10% initial Columbic efficiency increase of the LiFePO 4 electrode in a full cell configuration using the Pre-SEI graphite, compared with the pristine graphite anode. The electrochemical preformation of SEI on the graphite powders offers a complete solution to offset initial lithium loss without a sacrifice of active cathode material loading.

25 ENERGY STORAGE↗

DOE OSTI2023

Influence of carbon nanotubes on microstructure and corrosion performance of additively manufactured 316L stainless steel

For this study, laser powder bed fusion (LPBF) was performed on feedstock-modified 316L stainless steel powder with 1 and 2 vol% carbon nanotubes (CNT). The corrosion resistance was evaluated following cyclic potentiodynamic polarization tests conducted in 0.6 M NaCl at room temperature, 35 and 50 °C, and immersion tests in 6 % FeCl 3 . The CNT addition has increased the pitting potential and decreased number of pits formed during immersion in FeCl 3 solution, which could be attributed to Mn-Si-O nano inclusions refinement and segregation of chromium around the inclusions. The observed corrosion behavior was correlated with the altered microstructure due to CNT addition.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Conductive spinels derived from Co–Mn based alloy precursor for SOFC cathode-side contact application

The utilization of gas-atomized Co–Mn based alloy precursor is a promising approach to lowering the sintering temperature of the spinel contact layer and enhancing its performance. In this work, simulated interconnect/contact/cathode cells are employed to investigate the effects of different metallic precursors (i.e., three Co–Mn based alloy powders and a mixture of Co + MnO 2 powders) on the microstructure and performance of the reactively-sintered MnCo 2 O 4 -based contact layer. While excellent overall electrical performance is observed for all the cells with the four contact precursors during 1000-h testing at 800 °C in air, the cell with the Ce-doped alloy contact precursor shows the lowest cell area specific resistance (ASR) and ASR degradation rate. Cross-sectional observation of the tested cells is conducted to assess the compatibility of the contact layer with adjacent components as well as its effectiveness in reducing the Cr 2 O 3 scale growth and blocking Cr migration from the interconnect to the cathode.

08 HYDROGEN↗

DOE OSTI2020

Direct observation of pore formation mechanisms during LPBF additive manufacturing process and high energy density laser welding

Laser powder bed fusion (LPBF) is a 3D printing technology that can print parts with complex geometries that are unachievable by conventional manufacturing technologies. However, pores formed during the printing process impair the mechanical performance of the printed parts, severely hindering their widespread application. Here, we report six pore formation mechanisms that were observed during the LPBF process. Our results in this study reconfirm three pore formation mechanisms - keyhole induced pores, pore formation from feedstock powder and pore formation along the melting boundary during laser melting from vaporization of a volatile substance or an expansion of a tiny trapped gas. We also observe three new pore formation mechanisms: (1) pore trapped by surface fluctuation, (2) pore formation due to depression zone fluctuation when the depression zone is shallow and (3) pore formation from a crack. The results presented here provide direct evidence and insight into pore formation mechanisms during the LPBF process, which may guide the development of pore elimination/mitigation approaches. Since certain laser processing conditions studied here are similar to the situations in high energy density laser welding, the results presented here also have implications for laser welding.

42 ENGINEERING↗

DOE OSTI2020

Magnetic and mechanical properties of grain-refined Dy-free Nd-Fe-B sintered magnets

In this work, the effects of grain size on magnetic and mechanical properties of Dy-free Nd-Fe-B sintered magnets were studied. The grain size of the sintered magnets was varied by using different sized Dy-free Nd-Fe-B alloy feedstock powders which were ball milled to different extents. Increasing the ball milling time from 7 to 11 h caused the average particle size of the powders to decrease from 3.6 to 2.1 µm, while the average grain size of the corresponding sintered magnets decreased from 5.0 to 4.0 µm. The intrinsic coercivity Hcj and maximum energy product (BH) max of these magnets increased from 11.6 to 13.7 kOe and 41.6 to 43.6 MGOe, respectively. The finer grain magnets exhibited better thermal stability, as indicated by a smaller temperature coefficient of H cj (-0.71%/°C). With extending ball milling time to 15 h, the magnetic properties of the magnets deteriorate, while the flexural strengths first decrease and then increase. The flexural strength improvement is attributed to the increased Oxygen content in the magnets due to finer grains. The coercivity enhancement by reduction of grain size is a promising approach to develop Dy-free Nd-Fe-B sintered magnets with better thermal stability. It is important to control the Oxygen contents in the magnets to compromise both magnetic and mechanical properties.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Synthesis, structure and canted antiferromagnetism of layered cobalt hydroxide sorbate

Layered hybrid organic–inorganic compounds of the transition metal hydroxides, in which part of the hydroxide ions are exchanged for organic ligands that act as spacers of the 2-dimensional inorganic layers, elicit new or enhanced properties. The interlayer ligands enable fine-tuning of the physicochemical properties of the metal hydroxide layers, including their magnetism. Specifically, within the Co(OH) 2 family of transition ion hydroxides, this approach has been leveraged to stabilize antiferromagnetic and ferrimagnetic ground states for pillared and layered complexes, respectively. Here, in this work, we further investigate the effects of changing dimensionality, local Co coordination, and interlayer spacing on the magnetic ground state of brucite-like β-Co(OH) layered complexes. We report the hydrothermal synthesis of a new crystalline material, Co(OH)(sorb), where the inorganic layers are spaced by monotopic, doubly unsaturated sorbate ligands (sorb = [C 6 H 7 O 2 ] – ). The material was structurally characterized using powder X-ray and neutron diffraction measurements and the crystal structure was solved ab initio from powder diffraction data and refined using the Rietveld method. The magnetic susceptibility and magnetization measurements reveal canted antiferromagnetic ordering with T N = 41.7 K. This report augments our understanding of tuning magnetism through dimensionality in layered complexes and represents a step forward in the design of new 2D layered hybrid compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Localized orientation gradients in additively manufactured stainless steel 316H structures

The high solidification rates during additive manufacturing cause highly localized thermal and strain gradients. The effect of these gradients on the evolution of local orientation misorientations within a grain is not well understood. In this study, stainless steel 316H parts were fabricated via laser powder bed fusion using three different energy densities: 43, 71, and 135 J/mm 3 . Electron backscatter diffraction showed that the maximum misorientations of the grains can be up to 25° along the build direction. Misorientation gradients (RM g ) within grains are process-dependent and can change from 0.036°/μm to 0.015°/μm with increased volumetric energy densities. In conclusion, the characterized misorientation gradients are an indication of the level of dislocations and, to an extent, the plastic deformation resulting from the rapid solidification during laser powder bed fusion.

316H↗

DOE OSTI2024

Active interlocking metasurfaces enabled by shape memory alloys

Interlocking metasurfaces (ILMs) are a newly developed joining technology that relies on arrays of interlocking features that transmit force and constrain motion between adjoining bodies in one or more directions. This study explores harnessing the shape memory effect (SME) in Nickel-Titanium shape memory alloys (NiTi SMAs) in structures fabricated using additive manufacturing (AM) to advance the development of active ILMs by creating unit cells that open or close at specific temperatures. The study encompasses designing and fabricating two distinct interlocking array configurations using near-equiatomic NiTi powder and the laser powder bed fusion (L-PBF) AM technique, following a previously developed AM process optimization framework to manufacture defect-free parts. To guide the design process, finite element analysis (FEA) was employed to predict strain values during engage-disengage cycles. The martensitic transformation characteristics of the ILMs were characterized. Thermomechanical testing revealed that the ILMs demonstrate high locking force once engaged, coupled with complete shape recovery and good cyclic stability. Digital image correlation (DIC) was also employed to validate the FEA predictions during the engage-disengage cycles. The results indicate that NiTi SMA-based ILMs can be designed and fabricated into complex shapes using L-PBF. By leveraging the SME, the functionality of an ILM can be improved upon. The combination of computational modeling, additive manufacturing, and thermomechanical and physical property characterization provides a framework for designing future ILMs out of active materials.

Additive manufacturing↗

DOE OSTI2026

Enhancing microsegregation during rapid directional solidification through ternary microalloying

The nano-cellular dendritic microstructure formed during rapid directional solidification in powder bed fusion additive manufacturing creates unique properties such as simultaneous improvement in strength and ductility. However, process control of microsegregation features remains challenging due to low sensitivity of critical solidification mechanisms to process parameters. This study leverages microalloying to achieve large changes in dendrite composition, microstructure, and interdendritic zone width during laser powder bed fusion without modifying process parameters. CALPHAD simulations predict that the addition of Zr significantly steepens the solidus line of the dilute Cu-Cr alloy system, leading to enhanced Cr rejection into the melt and greater than 95% reduction in solubility of Cr in the solidified Cu matrix. Experimental validation using time-of-flight secondary ion mass spectrometry and Kelvin probe force microscopy reveals that the ternary alloy containing 0.01 wt% Zr exhibited wider interdendritic regions compared to the binary, a significantly higher number of Cr-rich particles within interdendritic regions, near-complete ejection of oxygen impurities from the matrix, and greater nanoscale work function contrast. These features indicate more aggressive Cr segregation in the presence of Zr and a purer Cu matrix and provide a potentially robust method for engineering the nano-cellular dendritic solidification microstructure.

CALPHAD↗

DOE OSTI2022

A systematic study and framework of fringe projection profilometry with improved measurement performance for in-situ LPBF process monitoring

Fringe Projection Profilometry (FPP) is a cost-effective and non-invasive technology that has been shown to measure finer features. Here, in this work, we developed an in-situ FPP method to measure the dynamic topography of powder bed and printed layer during Laser Powder Bed Fusion (LPBF) additive manufacturing (AM) process. A systematic study towards developing a comprehensive framework of LPBF-specific FPP is demonstrated to enhance and evaluate the performance of applying FPP for in-situ LPBF monitoring, including 1) a modified sensor model with localized correction; 2) improved phase unwrapping with FFT filtering 3) quantitative uncertainty analysis; and 4) experimental validation with ex-situ characterization. The developed LPBF-specific FPP system and methods are implemented on a commercial LPBF-AM machine, achieving better accuracy, more robustness, and increased field of view while maintaining sufficient measurement range and decent resolution, in contrast to literature methods. The established FPP framework will facilitate the development of closed-loop control strategies for advancing LPBF based AM.

42 ENGINEERING↗