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At least 523 records · Page 29

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NASA NTRS1987

Dynamic and static fatigue behavior of sintered silicon nitrides

The dynamic and static fatigue behavior of Kyocera SN220M sintered silicon nitride at 1000 C was studied. Fractographic analysis of the material failing in dynamic fatigue revealed the presence of slow crack growth (SCG) at stressing rates below 41 MPa/min. Under conditions of static fatigue this material also displayed SCG at stresses below 345 MPa. SCG appears to be controlled by microcracking of the grain boundaries. The crack velocity exponent (n) determined from both dynamic and static fatigue tests ranged from 11 to 16.

Chang, J.↗

NASA NTRS1992

Progress in the development of lightweight nickel electrode for aerospace applications

The NASA Lewis Research Center is currently developing nickel electrodes for nickel-hydrogen (Ni-H2) cells and batteries. These electrodes are lighter in weight and have higher specific energy than the heavy sintered state of the art nickel electrodes. In the present approach, lightweight materials or plaques are used as conductive supports for the nickel hydroxide active material. These plaques (fiber, felt, and nickel plated plastic) are fabricated into nickel electrodes by electrochemically impregnating them with active material. Initial performance tests include capacity measurements at five discharge levels, C/2, 1.0C, 1.37C, 2.0C, and 2.74C. The electrodes that pass the initial tests are life cycle tested at 40 and 80 percent depths of discharge (DOD). Different formulations of nickel fiber materials obtained from several manufacturers are currently being tested as possible candidates for nickel electrodes. Over 7,000 cycles of life cycle testing have been accumulated at 40 percent DOD, using the lightweight fiber electrode in a boiler plate Ni-H2 cell with stable voltage.

Britton, Doris L.↗

NASA NTRS2006

Thermal Dispersion Within a Porous Medium Near a Solid Wall

The regenerator is a key component to Stirling cycle machine efficiency. Typical regenerators are of sintered fine wires or layers of fine-wire screens. Such porous materials are contained within solid-waH casings. Thermal energy exchange between the regenerator and the casing is important to cycle performance for the matrix and casing would not have the same axial temperature profile in an actual machine. Exchange from one to the other may allow shunting of thermal energy, reducing cycle efficiency. In this paper, temperature profiles within the near-wall region of the matrix are measured and thermal energy transport, termed thermal dispersion, is inferred. The data show how the wall affects thermal transport. Transport normal to the mean flow direction is by conduction within the solid and fluid and by advective transport within the matrix. In the near-wall region, both may be interrupted from their normal in-core pattern. Solid conduction paths are broken and scales of advective transport are damped. An equation is presented which describes this change for a wire screen mesh. The near-wall layer typically acts as an insulating layer. This should be considered in design or analysis. Effective thermal conductivity within the core is uniform. In-core transverse thermal effective conductivity values are compared to direct and indirect measurements reported elsewhere and to 3D numerical simulation results, computed previously and reported elsewhere. The 3-D CFD model is composed of six cylinders in cross flow, staggered in arrangement to match the dimensions and porosity of the matrix used in the experiments. The commercial code FLUENT is used to obtain the flow and thermal fields. The thermal dispersion and effective thermal conductivities for the matrix are computed from the results.

Simon, T.↗

DOE OSTI2025

Mechanical Properties and Interfacial Bonding of Overmolded Polymer Composite Lattice Structures

This study investigates the mechanical properties and interfacial bonding of Polyamide 12 filled with Glass Fiber (PA12/GF) lattice structures overmolded with Nylon 66 (PA66) and Thermoplastic Polyurethane (TPU). The PA12/GF lattices, designed in Gyroid, Isotruss, and Octahedral geometries, were produced using the Selective Laser Sintering (SLS) technique. The thermal characteristics of both the lattice and overmolding materials were analyzed using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The mechanical performance and interfacial bonding were evaluated through mechanical testing and microstructural analysis. The results indicate that overmolding improved flexural strength and impact resistance of the PA12/GF lattices. For instance, the plain PA12/GF Isotruss lattice exhibited a flexural strength of 15.5 MPa. By overmolding it with TPU the flexural strength increased by up to 137%, while PA66-overmolding resulted in an increase of 371%, achieving a flexural strength of 73 MPa. In terms of impact resistance, TPU-overmolding improved performance significantly, with an increase of 1800% (Gyroid) compared to the plain lattice. Microstructural analysis revealed good adhesion at the interface, especially when both the lattice and overmolding materials were thoroughly dried prior to the overmolding process to minimize interfacial porosity. This study highlights the potential of using overmolding to enhance lattice structures performance, offering lightweight and cost-efficient solutions for automotive applications.

Talabi, Isaac [ORNL] (ORCID:0000000340215594)↗

DOE OSTI2026

Embedding Fiber Optic Sensors in Stainless Steel using Spark Plasma Sintering for Structural Health Monitoring in Harsh Environments

Embedded fiber optic sensors such as fiber Bragg gratings (FBGs) offer a unique route for distributed real-time in-situ imaging of various engineering parameters for numerous purposes. This study advanced the current sensor embedding approaches by exploring a spark plasma sintering (SPS)-assisted technology to embed FBGs in high-temperature structural materials and demonstrated the capability of temperature measurement. In this approach, single-mode FBGs were integrated into stainless steel (SS) 316L components using SPS, followed by the evaluation of the bonding quality between the FBGs and matrix, the optical attenuation of the fibers induced by embedding, and the sensing characters of the FBGs under temperature stimuli. The results demonstrated that superior bonding was achieved between the FBGs and highly-densified SS316L. Examination of the behavior of Bragg gratings validated signal fidelity after embedding. Real-time thermal imaging under temperature cycling using the FBGs demonstrated the effectiveness of the technique for smart materials manufacturing.

36 - MATERIALS SCIENCE↗

DOE OSTI2025

Tritium Breeder Composites for Fusion Applications

Due to the short half-life of tritium, all fusion reactors planned for long-term operation using a deuterium-tritium fuel cycle must produce sufficient tritium from reactions outside the core to maintain reactor operation. Typically, the core is surrounded by a tritium breeder blanket filled with lithium-containing materials which react under a neutron flux to form tritium that can then be collected. Here, reactor designers are forced to choose between using chemically reactive liquid breeders (e.g., Pb-Li, FLiBe, Li) or solid breeders, which often have lower lithium concentrations and questionable mechanical integrity under irradiation (e.g., Li4SiO4, Li2TiO3). To expand this pool of options, this work has sought to produce composite tritium breeder materials using lithium-containing ceramics and metal reinforcements. The resultant composite tritium breeders simultaneously feature higher lithium densities and improved mechanical integrity, including tensile strength and toughness, compared to other tritium breeders previously reported in literature.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2022

High temperature thick film sensor development based on doped lanthanum chromites refractory semiconductors materials

High temperature advanced sensing materials have generated high demand due the high accuracy temperature measurements requirements for process optimization, controlling and sensing. Some technological applications of harsh conditions sensing include monitoring tiles of space shuttles, rotating bearings in aircraft engines, turbines, jet engines dynamics and chemical reactors. High temperature conditions limit the sensing strategies, where typically traditional metal thermocouples are unstable, and the sensing options are limited to optical spectroscopy methods. Recently, refractory semiconductors thick- and thin-film thermocouples have been developed and, in many cases, preferred over conventional metallic thermocouples due their spatial resolution, and capability of direct deposition on any surface. Rare earth chromites ceramics materials, exhibit some properties of interest for high temperature sensing technologies development, such as: high microstructure and sintering stability, excellent conductive behavior at high temperatures, and matching thermal expansion coefficients relative to other conductors and refractory ceramics. In this work, high performance ultra-high temperature thermocouples using p-type and n-type doped lanthanum chromites materials were fabricated and tested at temperatures up to 1500 o C. Thermoelectric voltage, Seebeck Coefficients were established for all devices, evidencing high stability and performance in prolongated operational time and harsh conditions.

20 FOSSIL-FUELED POWER PLANTS↗

DOE OSTI2019

Influence of Particle Size on Apparent Diffusivity During Spark Plasma Sintering of Crystalline Powders

Abstract:: A theoretical framework is presented to determine an apparent diffusivity D during powder sintering and further elucidate the underlying interrelation between D and shrinkage behaviors of powders. Furthermore, to eliminate the influence of crystalline defects that are typically present in raw powders, complete crystallization of metallic glass powders is performed to allow the investigation of the influence of particle size solely on powder densification. Furthermore, to validate the framework developed, Ti{sub 40.6}Zr{sub 9.4}Cu{sub 37.5}Ni{sub 9.4}Sn{sub 3.1} crystalline alloy powders constituting particles with different sizes are examined to establish a correlation between D and the sintering behaviors of the powders. The findings show that the value of the apparent diffusivity D increases with the increasing particle size, which accelerates powder densification during spark plasma sintering. Furthermore, the results quantitatively support the argument that particle size can affect atomic diffusion during powder sintering.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Microstructure evolution during binder jet additive manufacturing of H13 tool steel

H13 is one of the most used tool steels for both hot and cold work tooling applications. Binder jet additive manufacturing offers the potential to deposit complex tools at scale due to larger powder bed sizes and faster deposition rates. However, to date there is no published literature on the sintering of H13 to full densification. Here, we discuss the pressureless sintering of binder jet AM H13 steel to full densification via supersolidus liquid phase sintering (SLPS) while presenting appropriate process windows (1360 °C – 1380 °C) for densification without distortion. The process windows have been rationalized based on thermodynamic calculations of liquid volume fractions with temperature. We show that higher binder saturation results in higher carbon retention and subsequently early liquid formation that can initiate the sintering process at lower temperatures. We report abnormal grain growth during sintering and found that the solidification phase transformations play a critical role on microstructural evolution and must be considered to accurately model the kinetics of SLPS.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Identifying higher oxygenate synthesis sites in Cu catalysts promoted and stabilized by atomic layer deposited Fe 2 O 3

The conversion of syngas to higher oxygenates is an important step in the pathway towards the long-term sustainable production of fuels and chemicals. Mixed Cu/Fe catalysts combine metals with different CO activation characteristics, a property that makes them promising candidates for higher oxygenate production. However, Cu/Fe catalysts suffer from instability due to sintering and phase separation, and the active sites for higher oxygenate formation on these materials are not well understood. In this work, we use atomic layer deposition (ALD) to modify silica-supported Cu nanoparticles with monolayer precise amounts of Fe 2 O 3 and study the effects on catalyst structure, reactivity, and stability. We demonstrate that the Fe 2 O 3 ALD process is inherently selective towards deposition on the SiO 2 surface versus the Cu nanoparticles. As a result, a sufficiently thick Fe 2 O 3 layer surrounding the Cu nanoparticles acts as a barrier against Cu migration, preventing catalyst deactivation through sintering without covering the Cu. In syngas conversion reactions, we find that higher oxygenate selectivity increases with Fe 2 O 3 loading at low and intermediate ALD cycle numbers. Furthermore, using in situ X-ray absorption spectroscopy, we demonstrate that the Fe near the Cu nanoparticles is reduced to a metallic state under reaction conditions. From these measurements, we identify these metallic Cu/Fe interfaces as the active sites for higher oxygenate formation, which are most abundant at intermediate Fe 2 O 3 ALD cycle numbers. As the Fe 2 O 3 loading increases, higher oxygenate selectivity falls, resulting from encapsulation of the Cu nanoparticles by thick Fe 2 O 3 layers. Overall, the results demonstrate how thickness-controlled ALD Fe 2 O 3 can be used as both a promoter and stabilizer of Cu-based higher oxygenate synthesis catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

A Sustainability-Based Expert System for Additive Manufacturing and CNC Machining

The objective of this research study is to develop a set of expert systems that can aid metal manufacturing facilities in selecting binder jetting, direct metal laser sintering, or CNC machining based on viable products, processes, system parameters, and inherent sustainability aspects. For the purposes of this study, cost-effectiveness, energy, and auxiliary material usage efficiency were considered the key indicators of manufacturing process sustainability. The expert systems were developed using the knowledge automation software Exsys Corvid ® V6.1.3. The programs were verified by analyzing and comparing the sustainability impacts of binder jetting and CNC machining during the fabrication of a stainless steel 316L component. According to the results of this study, binder jetting is deemed to be characterized by more favorable indicators of sustainability in comparison to CNC machining, considering the fabrication of components feasible for each technology.

36 MATERIALS SCIENCE↗

NASA NTRS2016

An Assessment of Nondestructive Evaluation Capability for Complex Additive Manufacturing Aerospace Components

The primary focus of this work is to investigate some of the fundamental relationships between processing, mechanical testing, materials characterization, and NDE for additively manufactured (AM) components using the powder bed fusion direct melt laser sintered process. The goal is to understand the criticality of defects unique to the AM process and then how conventional nondestructive evaluation methods as well as some of the more non-traditional methods such as computed tomography, are effected by the AM material. Specific defects including cracking, porosity and partially/unfused powder will be addressed. Besides line-of-site NDE, as appropriate these inspection capabilities will be put into the context of complex AM geometries where hidden features obscure, or inhibit traditional NDE methods.

Walker, James↗

DOE OSTI2020

Techno-economic analysis of cathode material production using flame-assisted spray pyrolysis

The cost of cathode materials contributes approximately 32.7% of the total cell construction cost of lithium-ion batteries, significantly affecting the price of battery packs. To reduce the cathode material manufacturing cost, a flame-assisted spray pyrolysis (FSP) method has been developed to utilize a sustainable solvent of glycerol to manufacture the LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC333) cathode materials. The purpose of this study is to evaluate the minimum cathode material selling price (MCSP) of the FSP processes compared with a traditional carbonate co-precipitation pathway. Results show that the MCSP of the FSP is $\$$19.1/kg that is 17% lower than the traditional carbonate co-precipitation pathway as a result of lower fixed operating cost and variable overhead. Sensitivity analysis shows that when the new process is integrated with in-situ sintering and processing, the MCSP can be as low as $\$$15.6/kg. When all the material prices are decreased by 20%, the FSP process can synthesize NMC333 at a price of $\$$2.3/kg lower. According to the simulation result, LiNi 0·8 Mn 0·1 Co 0·1 O 2 (NMC811) has the best potential to meet the U.S. Department of Energy battery price target of $\$$125/kWh, demonstrating that the FSP process is an attractive manufacturing technology for NMC cathode powder material production.

25 ENERGY STORAGE↗

DOE OSTI2024

In-situ synchrotron X-ray diffraction of hydroxyapatite-zirconia composite during conventional and flash sintering

Here, we conducted in-situ X-ray diffraction to study the crystalline phase evolution in hydroxyapatite-zirconia composites during both conventional and flash sintering processes. Additionally, we examined the thermal history and microstructure of the composite under these sintering conditions. Despite both sintering methods reaching similar average temperatures, they yielded distinct results in terms of crystalline phase composition and microstructure. In the flash sintered samples, we observed a complete transformation of hydroxyapatite into α- tricalcium phosphate and a complete tetragonal to cubic phase transition in zirconia. Conversely, the conventionally sintered samples remained practically stable. Notably, the flash sintered samples exhibited needle-like microstructures, which were absent in their conventionally sintered counterparts. This divergence suggests that the application of an electric field plays a role in generating athermal effects during the sintering of hydroxyapatite-zirconia composites.

36 MATERIALS SCIENCE↗

DOE OSTI2020

UO 2 + 5 vol% ZrB 2 nano composite nuclear fuels with full boron retention and enhanced oxidation resistance

The boron isotope ( 10 B) can be used as a neutron absorber in UO 2 to control the reactivity of nuclear fuel pellets, however, the boron source can react with oxygen source in UO 2 to form B 2 O 3 that vaporize readily at temperatures above 1200 °C. Unfortunately, the sintering of UO 2 fuel requires hours holding at high temperature (>1700 °C), resulting in an inevitable B loss during sintering and unpredictable B concentration in final product. It is challenging to incorporate boron through a conventional sintering method. In this work, we demonstrated that spark plasma sintering (SPS), a field assisted sintering technology, can effectively densify UO 2 + 5 vol% ZrB 2 composite fuel pellets by rapid consolidation at 1600 °C for a short duration of 5 min under an applied pressure of 40 MPa. Further, thermogravimetric analysis (TGA) measurements confirm that ZrB 2 is fully retained inside the composite fuel pellets. Inside the composite fuel pellets, nano sized ZrB 2 particles are uniformly distributed along the grain boundaries of the UO 2 matrix. The ZrB 2 particle transforms to a glassy B 2 O 3 phase covering the sample surface and grain boundaries of UO 2 matrix after a simple post-sintering annealing at 1000 °C in flowing Argon gas for 4 h. The formed glassy B 2 O 3 slows down the diffusion of oxygen ions and postpones the onset temperature for oxidation of UO 2 from 400 °C to 550 °C. This study demonstrates the capability of SPS, an advanced fuel manufacturing technique, to achieve a full retention of ZrB 2 in UO 2 oxide fuel and increase oxidation resistance through a simple post-sintering annealing. The reported work holds great engineering potential for development of advanced oxide fuel for nuclear application.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2024

Processing and characterization of the homologous Zr x Ta 2 O 2x+5 series

In this study, Zr x Ta 2 O 2x+5 (ZTOx) was systematically studied to determine ideal solid-state synthesis and pressureless sintering conditions. For Zr 6 Ta 2 O 17 (ZTO6) and other compositions with values of x in ZTOx the optimal synthesis temperature of 1100 °C with 1 h dwell time was optimal. XRD phase analysis of the homologous series indicated that for ZTOx, x = 5, 6, 7, and 8 were within the phase stability field while x = 4 and x = 9 were outside the phase stability field. Unit cell lattice parameters changed anisotropically with Zr:Ta ratio with an overall <0.1% change in unit cell volume across the solid solution. Some Raman modes red shifted while others blue shifted, indicating competing tensile and compressive strains. Sintering of ZTOx required a progressively higher temperature as Zr-content increased despite the same starting powder grain sizes and synthesis temperature. Higher Vickers hardness for Zr-rich (12.7–12.8 GPa) than Ta-rich Zr x Ta 2 O 2x+5 (11.6–11.7 GPa) disappeared when accounting for different sintering temperatures. Indentation toughness was similar for all compositions (1.2–1.4 MPa m 1/2 ). Properties of Zr x Ta 2 O 2x+5 series indicate tunability of Zr:Ta composition ratio while maintaining the structure and room temperature mechanical properties comparable to Hf 6 Ta 2 O 17 and 8 mol% yttria stabilized zirconia ceramics.

36 MATERIALS SCIENCE↗

NASA NTRS1973

High gas velocity burner tests on silicon carbide and silicon nitride at 1200 C

Specimens of silicon carbide and silicon nitride were exposed to a Mach one gas velocity burner simulating a turbine engine environment. Cyclic tests up to 100 hour duration were conducted at specimen temperatures of 1200 C. A specimen geometry was used that develops thermal stresses during thermal cycling in a manner similar to blades and vanes of a gas turbine engine. Materials were compared on a basis of weight change, dimensional reductions, metallography, fluorescent penetrant inspection, X-ray diffraction analyses, failure mode, and general appearance. One hot pressed SiC, one reaction sintered SiC, and three hot pressed Si3N4 specimens survived the program goal of 100 one-hour cycle exposures. Of the materials that failed to meet the program goal, thermal fatigue was identified as the exclusive failure mode.

Sanders, W. A.↗

DOE OSTI2022

CO 2 Laser Sintering of Garnet-Type Solid-State Electrolytes

We report the processing of garnet-type solid-state electrolytes remains challenging as densification conventionally requires high sintering temperatures and long processing times, which can result in severe Li loss, the formation of secondary phases, and thus high porosity and low ionic conductivity. Here, we report an ultrafast sintering method based on CO 2 laser scanning with the assistance of a heating stage. We demonstrate the rapid densification of low-packing-density Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) films, which are difficult to densify by conventional furnace sintering methods. This unique approach has three fingerprint characteristics: (1) mitigation of Li loss through ultrafast sintering (dwelling time $\ll$1 s); (2) a unique anisotropic shrinkage behavior that greatly reduces film thickness; (3) wave-like surface topology from point scanning strategy that enables 3D interfacial contacts with electrode materials. Herein, highly dense (95.68%) and highly conductive (0.26 mS·cm –1 at 25 °C) LLZTO films are obtained through CO2 laser sintering. This work provides a unique, scalable, and widely applicable ultrarapid laser sintering technique to overcome the difficulties associated with classic methods for the integration of SSEs for practical all-solid-state Li-metal battery applications.

36 MATERIALS SCIENCE↗