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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Review of additive manufacturing and densification techniques for the net- and near net-shaping of geometrically complex silicon nitride components

Silicon nitride (Si 3 N 4 ) is an advantageous material due its unique combination of mechanical, thermal, chemical, and electrical properties both at ambient and elevated temperatures. Because of these properties there are a wide range of applications for Si 3 N 4 components. Applications include heat exchangers, environmental barrier coatings, osteointegration scaffolds, radomes, and integrated circuitry. Furthermore, such applications often require geometric complexity for efficient and/or effective operation. However, traditional ceramics processing methods such as hot-pressing or die extrusion are typically limited to simple axis-symmetric shapes. With the advent of additive manufacturing, there has been significant advancement into the forming of geometrically complex Si 3 N 4 components. This review documents additive manufacturing advancements that have demonstrated, or are capable of, fabricating Si 3 N 4 components with complex geometry.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Impact of Mixed Feedstocks and Feedstock Densification on Ionic Liquid Pretreatment Efficiency

Background: Lignocellulosic biorefineries must be able to efficiently process the regional feedstocks that are available at cost-competitive prices year round. These feedstocks typically have low energy densities and vary significantly in composition. One potential solution to these issues is blending and/or densifying the feedstocks in order to create a uniform feedstock. Results/discussion: We have mixed four feedstocks - switchgrass, lodgepole pine, corn stover, and eucalyptus - in flour and pellet form and processed them using the ionic liquid 1-ethyl-3-methylimidazolium acetate. Sugar yields from both the mixed flour and pelletized feedstocks reach 90% within 24 hours of saccharification. Conclusions: Mixed feedstocks, in either flour or pellet form, are efficiently processed using this pretreatment process, and demonstrate that this approach has significant potential.

09 BIOMASS FUELS↗
DOE OSTI2021

Biomass Size Reduction, Drying, and Densification

The overall objective is to solve the particle attrition issue during biomass grinding and pelleting and to enable pelleting as a viable option for production of on-spec material or conversion-ready cellulosic feedstocks.

09 BIOMASS FUELS↗
DOE OSTI2024

Operando Investigation on the Role of Densification and Chemo-Mechanics on Solid-State Cathodes

All solid-state batteries are desirable for a range of energy storage applications which require high energy density. Achieving a high energy density in a solid-state battery requires the operation of an energy dense anode with a composite solid-state cathode. Pores and/or voids within a solid state cathode are ion-blocking and thus control over the concentration and distribution of pores in the initial electrode and cycled electrode is desirable. This study provides an understanding of the interplay between electrode microstructure and mechanics on active material utilization in solid state cathodes composed of NCM 811 and Li 6 PS 5 Cl. Decreasing the solid electrolyte particle size leads to greater active material-electrolyte contact and less total deformation when exposed to an external load. Composite cathodes with greater compliance can potentially decrease strain between the active material and solid electrolyte, decrease delamination events and result in higher overall active material utilization and high capacity retention.

25 ENERGY STORAGE↗
DOE OSTI2018

Vacuum Pressureless Sintering of Ti-6Al-4V Alloy with Full Densification and Forged-Like Mechanical Properties

Ti-6Al-4V ingots with a nearly 100% density, fine and homogeneous basket-weave microstructure, and better comprehensive mechanical properties (UTS = 935 MPa, Y.S. = 865 MPa, El. = 15.8%), have been manufactured by vacuum pressureless sintering of blended elemental powders. Coarse TiH{sub 2} powder, Al powder (2, 20 μm), V powder, and Al-V master alloy powder were used as raw materials to produce different powder mixtures (D{sub 50} = 10 μm). Then, the compacts made by cold isostatic pressing were consolidated by different sintering curves. A detailed investigation of different as-sintered samples revealed that a higher density can be obtained by generating transient molten Al in the sintering process. Coarse Al powder and a rapid heating rate under the melting point of Al contribute to molten Al formation. The presence of temporary liquid phase changes the sintering mechanism, accelerating the sintering neck formation, improving sinterability of the powder mixtures. Density of 99.5% was achieved at 1150 °C, which is markedly lower than the sintering temperatures reported for conventional blended elemental powder metallurgy routes. In addition, low interstitial content, especially for oxygen (0.17 wt.%), is obtained by strict process control.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Densification and oxidation behavior of spark plasma sintered Hafnium Diboride-Hafnium Carbide composite

This study reports on the sintering and oxidation behaviors of Hafnium Diboride (HfB 2 ) and Hafnium Carbide (HfC) based ultra-high temperature ceramic (UHTC) composites. Pure Hafnium Diboride, Hafnium Carbide, and HfB 2 -50 vol% HfC composite were consolidated using spark plasma sintering (SPS) without the use of sintering aids. HfB 2 -HfC composite displayed a high sintered density of 98% as compared to 87% density of pure HfB 2 . The increased density of the HfB 2 -HfC composite is attributed to the bimodal powder distribution, which allowed for the smaller HfC particle to occupy the voids between the larger HfB 2 particles resulting in improved packing efficiency. Moreover, the higher planar surface energy, for the (111) and the (200) planes for HfC, contributed to the smaller HfC particle being a significant driving force in the sintering process. Oxidation studies of each material were carried out by exposing them to a high-speed plasma jet in a temperature exceeding 2700 °C. The results of these studies show an improved oxidation resistance of HfB 2 -HfC composite by 54% and 70% over pure HfC and HfB 2 , respectively. The enhanced oxidation behavior is attributed to B 2 O 3 filling in the porosity between the HfO 2 scale and protecting the underlying material. This study provides a new alternative to improve the sinterability of UHTC diborides by introducing another UHTC (i.e., HfC) to form a fully dense composite without sintering aid and superior oxidation resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Siloxane-modified polycarbosilane flexible Prepregs for fabrication of ceramic matrix composites via compression molding and PIP densification

For this work, the development of ceramic matrix composites (CMCs) using 5 harness satin carbon fiber fabric impregnated with commercial polycarbosilane precursor plasticized by siloxane copolymer was investigated aiming to improve wetting behavior and shape conformability. The polycarbosilane precursor and polysiloxane plasticizer were mixed at varying weight ratios to obtain flexible preceramic resin prepreg cloths. 13 plies of preceramic polymer prepreg cloths were stacked in 0/90° layup and cured by compression molding, followed by densified via PIP process. The CMCs were densified with eight PIP cycles followed by final crystallization at 1600 °C. The CMCs made with 10 wt% polysiloxane loading showed lower viscosity of the prepreg resin as well as higher strength and displacement to failure compared to those fabricated from unplasticized polycarbosilane prepolymer. In contrast, at higher concentration of plasticizer, viscosity of the prepreg resin increased, and the CMC became more brittle; however, it exhibited considerably higher thermal conductivity.

Carbosilane↗
DOE OSTI2022

A process optimization framework for laser direct energy deposition: Densification, microstructure, and mechanical properties of an Fe-Cr alloy

Laser Direct Energy Deposition (DED) is a metal additive manufacturing technique with the ability to fabricate large and complex parts through deposition of metal powders. However, achieving high-density parts and targeted build heights using DED can be challenging due to the large number of highly sensitive process variables. This work proposes a robust fabrication parameter optimization framework to generate process maps for primary parameters in DED, including laser power, scan speed, mass flow rate, hatch spacing, and layer height. Simple single-track experiments were utilized to map out the parameter space, and a combination of geometric criteria for hatch spacing and layer height were proposed to determine parameter sets that achieve both targeted build heights and mitigate porosity formation. Using this framework, specimens with >99 % density and consistent mechanical properties were successfully fabricated over a wide range of process parameters for an Fe-9wt.%Cr (Fe9Cr) alloy, a surrogate for radiation damage-resistant reduced activation ferritic/martensitic (RAFM) steels. Processing these materials using DED is of particular interest in the development of plasma facing components for nuclear fusion applications. The microstructure and mechanical properties of as-printed Fe9Cr were characterized using optical and electron microscopy, X-ray diffraction, and uniaxial tensile tests. As-printed Fe9Cr displayed ~25 % elongation and ultimate tensile strengths of up to 475 MPa which is comparable to similar wrought alloys. Finally, the proposed framework will allow for accelerated DED parameter optimization for novel alloy systems, as well as open the possibility for local microstructure control while simultaneously mitigating defect formation.

42 ENGINEERING↗
DOE OSTI2013

On the densification of cubic ZrO{sub 2} nanocondensates by capillarity force and turbostratic C–Si–H multiple shell

A turbostratic C–Si–H lamellar phase with 0.35–0.39 nm interspacing and ZrO{sub 2} condensates having cubic (c), tetragonal and monoclinic structures stabilized by increasing particle size were synthesized by pulsed laser ablation on Zr plate in TEOS and characterized by X-ray/electron diffraction and optical spectroscopy. The c-ZrO{sub 2} phase ca. 10% denser than the ambient lattice was stabilized as 3–10 nm sized cubo-octahedral nanoparticles but as abnormal large-sized (up to 30 nm) ones when encapsulated by the C{sub 1−x}Si{sub x}:H multiple shell with defective graphite-like structure units to exert an effective compressive stress. The potential application of such core–shell nanostructure with enhanced binding of Zr and O ions and implication for natural dynamic occurrence of the C{sub 1−x}Si{sub x}:H phase are addressed. - Graphical abstract: Lattice image of a typical cubic-ZrO{sub 2} particle densified by the turbostratic Si{sub x}C{sub 1−x}:H shell. Highlights: ► Turbostratic C–Si–H lamellar phase and ZrO{sub 2} condensates were synthesized by PLA. ► The c-ZrO{sub 2} phase ca. 10% denser than the ambient lattice was stabilized as 3–10 nm. ► The c-ZrO{sub 2} particles up to 30 nm were densified when encapsulated by the C{sub 1−x}Si{sub x}:H multiple shell. ► Tight ion binding of the c-ZrO{sub 2} due to capillarity force and turbostratic shell.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Microstructural study and densification analysis of hot work tool steel matrix composites reinforced with TiB{sub 2} particles

Hot work tool steels are characterized by good toughness and high hot hardness but are less wear resistant than other tooling materials, such as high speed steel. Metal matrix composites show improved tribological behavior, but not much work has been done in the field of hot work tool steels. In this paper TiB{sub 2}-reinforced hot work tool steel matrix composites were produced by spark plasma sintering (SPS). Mechanical alloying (MA) was proposed as a suited process to improve the composite microstructure. Density measurements and microstructure confirmed that MA promotes sintering and produces a fine and homogeneous dispersion of reinforcing particles. X-ray diffraction patterns of the sintered composites highlighted the formation of equilibrium Fe{sub 2}B and TiC, as predicted by thermodynamic calculations using Thermo-Calc® software. Scanning electron microscopy as well as scanning Kelvin probe force microscopy highlighted the reaction of the steel matrix with TiB{sub 2} particles, showing the formation of a reaction layer at the TiB{sub 2}-steel interface. Phase investigations pointed out that TiB{sub 2} is not chemically stable in steel matrix because of the presence of carbon even during short time SPS. - Highlights: • TiB{sub 2} reinforced steel matrix composites were produced by spark plasma sintering. • TiB{sub 2} was successfully dispersed in the steel matrix by mechanical alloying. • Steel and TiB{sub 2} react during sintering forming equilibrium Fe{sub 2}B and TiC. • The new phases were investigated by means of AFM, Volta potential and XRD analyses.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Studies on densification, mechanical, micro-structural and structure–properties relationship of magnesium aluminate spinel refractory aggregates prepared from Indian magnesite

The present work intends to study the development of magnesium aluminate spinel aggregates from Indian magnesite in a single firing stage. The raw magnesite has been evaluated in terms of chemical analysis, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, and X-ray diffraction. The experimental batch containing Indian magnesite and calcined alumina has been sintered in the temperature range of 1550 °C–1700 °C. The sintered material has been characterized in terms of physico-chemical properties like bulk density, apparent porosity, true density, relative density and thermo-mechanical/mechanical properties like hot modulus of rupture, thermal shock resistance, cold modulus of rupture and structural properties by X-ray diffraction in terms of phase identification and evaluation of crystal structure parameters of corresponding phases by Rietveld analysis. The microstructures developed at different temperatures have been analyzed by field emission scanning electron microscope study and compositional analysis of the developed phase has been carried out by energy dispersive X-ray study. - Highlights: • The studies have been done to characterize the developed magnesium aluminate spinel. • The studies reveal correlation between refractory behavior of spinel and developed microstructures. • The studies show the values of lattice parameters of developed phases.

36 MATERIALS SCIENCE↗