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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 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Exploring As-Cast PbCaSn-Mg Anodes for Improved Performance in Copper Electrowinning

Lead calcium tin (PbCaSn) alloys are the common anodes used in copper electrowinning (Cu EW). Given a large amount of energy consumed in Cu EW process, anodes with controlled oxygen evolution reaction (OER) kinetics and a lower OER overpotential are advantageous for reducing the energy consumption. To date, magnesium (Mg) has never been studied as an alloying element for EW anodes. As-cast PbCaSn anodes with the addition of Mg were examined herein, revealing an improved performance compared to that of the industrial standard PbCaSn anode. The alloy performances in the early stages of anode life and passivation were established from electrochemical studies which were designed to simulate industrial Cu EW process. The 24-hour polarization testing revealed that the Mg alloying depolarizes the anode potential up to 80 mV; thus, resulting in a higher Cu EW efficiency. In addition, scanning electron microscopy and X-ray photoelectron spectroscopy revealed that the alteration of the alloy microstructure and the corresponding interfacial reactions contribute to the changes of the anode electrochemical performances. The present study reveals for the first time the potency of Mg alloying in reducing the overpotential of PbCaSn anode.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Study of the Mechanism of Liquid Slag Infiltration for Lubrication in Slab Continuous Casting

Consistent and uniform lubrication of the solidifying shell, especially in the meniscus, is crucial for the smooth continuous casting operation and production of strands free of surface defects. Thus, the current study established a coupled model to study the inflow behavior of liquid slag to the mold-strand channel, taking the solidification of steel and slag and the periodic oscillation of mold into account. The difficulties and solutions for the simulation were described in detail. The predicted profiles of the slag rim and initial shell were in good agreement with the reports. The main results indicated that liquid slag could be squeezed out and back into the slag pool in a negative strip period while a large amount of liquid slag could infiltrate into the mold-strand channel. Thus, the amount of slag consumed in the negative strip period was relatively small compared with that in the positive strip period. The predicted variation of slag consumption during mold oscillation was periodic, and the average value was 0.274 kg/m{sup 2}, which agreed well with the slag consumption in industrial practice. The current model can predict and optimize the oscillation parameters aiming at stable lubrication conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Hydrogen Addition on Softening and Melting Reduction Behaviors of Ferrous Burden in Gas-Injection Blast Furnace

The softening and melting reduction behaviors of ferrous burden in a gas-injection blast furnace (BF) have been investigated experimentally with the assistance of H{sub 2}. The results indicate that the initial softening temperature of the burden in the BF is lower than that in the traditional BF, while the opposite trend is observed for its melting and dripping temperatures, thus widening the softening range and narrowing the melting zone. As a result, the permeability of the stock column is apparently improved, owing to the decreased amount of the produced melt. After H{sub 2} gas is added, the thickness of the iron shell of the burden pellet increases, and the quantity of its liquid wüstite core decreases due to the higher reduction degree. The reduction rate of iron oxides is much faster than the carburization rate with the H{sub 2} addition, and the dripping behavior of the ferrous burden is determined by the carburization with a high reduction potential. After taking into account the effects of H{sub 2} addition on the iron oxide reduction rate, melt quantity, burden microstructure, and energy consumed by the gas-injection BF, it has been concluded that the optimal H{sub 2} content lies in the range between 10 and 15 pct.

36 MATERIALS SCIENCE↗
DOE OSTI2019

In Situ Monitoring of Pit Gas Composition During Baking of Anodes for Aluminum Electrolysis

Carbon anodes, which are consumed in aluminum electrolysis, are fabricated in separate anode plants where coke and pitch are mixed and vibrocompacted to green anode blocks before being baked in anode baking furnaces. The chemical environment inside an anode baking furnace is found to play an important role in the degradation of the furnace refractory lining. In this work, the pit gas composition was recorded during anode baking by a Fourier transformed infrared spectroscopy (FTIR) spectrometer and a gas chromatograph. The temperature dependence of the concentration of gas species during baking was obtained based on three measurement campaigns. The concentrations of CO and CO{sub 2} were found to be dependent on temperature, where the concentration of CO peaked around the maximum firing temperature. In addition to varying concentrations of CH{sub 4} and HF, water was found in large amounts in the first part of the baking cycle. The water originates to some extent from the cooling of the green anodes after vibrocompaction and is potentially important with respect to the chemical stability of the refractory lining. The variations in pit gas composition are related to operational parameters and are discussed in relation to refractory degradation phenomena.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Characteristics of Slag Infiltration in High-Mn Steel Castings

To determine the composition difference between the solid and liquid films in plant practice for high-Mn steel castings, a reaction experiment was carried out to investigate the composition profile of MnO and SiO{sub 2} in the slag layer. Based on the experimental results, a mathematical model of the mold slag for high-Mn steel was developed to describe the nonuniform infiltration behavior of mold slag during oscillation cycles. Moreover, the effects of uneven slag films on slab lubrication and heat transfer in the mold are discussed. The results show that the concentrations of MnO and SiO{sub 2} over the flux layer have an opposite stair-step distribution, which consists of a reaction layer and nonreaction layer. When the reaction layer thickness is 5 mm, a thicker liquid film is formed between the slab and the mold. The inhomogeneity of the composition in the solid film causes large fluctuations in the heat flux in the mold, resulting in irregular depressions on the shell surface. With a reacting thickness of 10 mm, the reacting slag fills in the gap to generate a thinner solid film, which increases the overall heat flux in the mold. Since mold oscillation combined with slag rim enhances the pressure flow in the vicinity of the meniscus, the liquid slag within 80 mm of the mold wall is mixed and consumed quickly. In contrast, the liquid slag beyond 80 mm from the mold wall with a low velocity stays longer in the liquid pool. The model predictions illuminate the characteristics of slag infiltration during high-Mn steel casting, showing good agreement with plant measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Evolution of Oxide Inclusions in Si-Mn-Killed Steel During Protective Atmosphere Electroslag Remelting

The current study was motivated to reveal the evolution of MnO-SiO{sub 2}-Al{sub 2}O{sub 3} inclusions during protective atmosphere electroslag remelting (P-ESR), and the effect of slag composition on the inclusion evolution. The oxide inclusions in the consumable steel electrode were ternary (7.1-26.4 mass pct) MnO-(53.3-82.8 mass pct) SiO{sub 2}-(8.3-23.1 mass pct) Al{sub 2}O{sub 3} without exception, which were fully removed during the P-ESR in two ways: a portion of these inclusions were dissociated in its individual chemical species into liquid steel, whereas the others were removed by absorbing them into molten slag before liquid metal droplets collected in liquid metal pool during P-ESR. The oxide inclusions both in liquid metal pool and in remelted ingots are mostly MgAl{sub 2}O{sub 4} (containing about 3 mass pct MgO) and Al{sub 2}O{sub 3} inclusions, irrespective of the SiO{sub 2} contents (1.9 to 9.0 mass pct) in the slag. These inclusions readily formed in the liquid metal pool as a result of the reaction between alloying elements and the dissolved oxygen in liquid steel that dissociated from MnO-SiO{sub 2}-Al{sub 2}O{sub 3} inclusions.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Comparison of Extensive Thermal Cycling Effects on Microstructure Development in Micro-alloyed Sn-Ag-Cu Solder Joints

Pb-free solder alloys based on the Sn-Ag-Cu (SAC) ternary eutectic have promise for widespread adoption across assembly conditions and operating environments, but enhanced microstructural control is needed. Micro-alloying with elements such as Zn was demonstrated for promoting a preferred solidification path and joint microstructure earlier in simple (Cu/Cu) solder joints studies for different cooling rates. This beneficial behavior now has been verified in reworked ball grid array (BGA) joints, using dissimilar SAC305 (Sn-3.0Ag-0.5Cu, wt.%) solder paste. After industrial assembly, BGA components joined with Sn-3.5Ag-0.74Cu-0.21Zn solder were tested in thermal cycling (-55 C/+125 C) along with baseline SAC305 BGA joints beyond 3000 cycles with continuous failure monitoring. Weibull analysis of the results demonstrated that BGA components joined with SAC + Zn/SAC305 have less joint integrity than SAC305 joints, but their lifetime is sufficient for severe applications in consumer, defense, and avionics electronic product field environments. Failure analysis of the BGA joints revealed that cracking did not deviate from the typical top area (BGA component side) of each joint, in spite of different Ag3Sn blade content. Thus, SAC + Zn solder has not shown any advantage over SAC305 solder in these thermal cycling trials, but other characteristics of SAC + Zn solder may make it more attractive for use across the full range of harsh conditions of avionics or defense applications.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Homogenizing Advanced Alloys: Thermodynamic and Kinetic Simulations Followed by Experimental Results

Segregation of solute elements occurs in nearly all metal alloys during solidification. The resultant elemental partitioning can severely degrade as-cast material properties and lead to difficulties during post-processing (e.g., hot shorts and incipient melting). Many cast articles are subjected to a homogenization heat treatment in order to minimize segregation and improve their performance. Traditionally, homogenization heat treatments are based upon past practice or time-consuming trial and error experiments. Through the use of thermodynamic and kinetic modeling software, NETL has designed a systematic method to optimize homogenization heat treatments. Use of the method allows engineers and researchers to homogenize casting chemistries to levels appropriate for a given application. The method also allows for the adjustment of heat treatment schedules to fit limitations on in-house equipment (capability, reliability, etc.) while maintaining clear numeric targets for segregation reduction. In this approach, the Scheil module within Thermo-Calc is used to predict the as-cast segregation present within an alloy, and then diffusion controlled transformations is used to model homogenization kinetics as a function of time and temperature. Examples of computationally designed heat treatments and verification of their effects on segregation and properties of real castings are presented.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evaluation of Strain–Life Fatigue Curve Estimation Methods and Their Application to a Direct-Quenched High-Strength Steel

Methods to estimate the strain–life curve, which were divided into three categories: simple approximations, artificial neural network-based approaches and continuum damage mechanics models, were examined, and their accuracy was assessed in strain–life evaluation of a direct-quenched high-strength steel. All the prediction methods claim to be able to perform low-cycle fatigue analysis using available or easily obtainable material properties, thus eliminating the need for costly and time-consuming fatigue tests. Simple approximations were able to estimate the strain–life curve with satisfactory accuracy using only monotonic properties. The tested neural network-based model, although yielding acceptable results for the material in question, was found to be overly sensitive to the data sets used for training and showed an inconsistency in estimation of the fatigue life and fatigue properties. The studied continuum damage-based model was able to produce a curve detecting early stages of crack initiation. This model requires more experimental data for calibration than approaches using simple approximations. As a result of the different theories underlying the analyzed methods, the different approaches have different strengths and weaknesses. However, it was found that the group of parametric equations categorized as simple approximations are the easiest for practical use, with their applicability having already been verified for a broad range of materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced Impact Toughness at Ambient Temperatures of Ultrafine-Grained Al-26 wt.% Si Alloy Produced by Equal-Channel Angular Pressing

Overcoming general brittleness of hypereutectic Al-Si alloys is in urgent need for expanding their application in automotive, aerospace and construction industries. A unique phenomenon was observed that bulk ultrafine-grained Al-26 wt.% Si alloy, produced by severe plastic deformation via equal-channel angular pressing, exhibited higher toughness at the impact temperature of − 196 ~ 100 °C than the coarse-grained casting alloy. The improvement in impact toughness at all testing temperatures was mainly due to the homogeneous ultrafine-grained structure with the breakage of brittle primary silicon crystals, which generated more and deeper fracture dimples that consumed much higher fracture energy. It indicates the advantage of bulk ultrafine-grained Al-Si alloys and spurs their application interest at various ambient temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Thermoelectric Properties of TiNiSn Half Heusler Alloy Obtained by Rapid Solidification and Sintering

Thermoelectric TiNiSn-based half Heusler compound reveals high Seebeck coefficient and electrical conductivity, leading to high power factor. As a consequence of the solidification path, TiNiSn single phase cannot be obtained directly from the liquid phase. Thus, a long annealing step is needed to homogenize the alloy. In this work, we present a new processing route for half Heusler compound formation, combining arc melting of pure elements, rapid solidification of the molten alloy and sintering. Rapid solidification of the molten alloy allows to obtain almost single TiNiSn phase, limiting the formation of the primary TiNi{sub 2}Sn phase as a consequence of the deep undercooling of the liquid. The rapidly solidified alloy was ground to powder and sintered by open die pressing. As-sintered samples show a density around 95% of the theoretical value. Thermal cycling of the sintered samples shows evolution of the phases, suggesting that after sintering the sample is not in equilibrium yet. After the second thermal cycle thermoelectric properties become reproducible, indicating the attainment of the equilibrium. In conclusion, the proposed processing route allows to obtain dense TiNiSn in bulk form avoiding the time-consuming annealing step, typically used to homogenize this alloy after solidification.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Experimental Analysis of the Crushing of Honeycomb Cores Under Compression

This paper presents an experimental study of the compressive response of hexagonal honeycomb core from the initial elastic regime to a fully crushed state. To understand the crushing mechanism, aluminum honeycomb core was compressed quasi-statically between rigid platens under displacement control. Honeycomb test specimens made of aluminum alloy with different configurations such as cell size, cell number, core density, and specimen size have been tested. During the crushing, the cells buckle elastically and collapse at a higher stress due to inelastic action, after the cells crush by progressive formation of folds on cell walls. The response densifies when folds consume the whole panel height. The peak load recorded during tests corresponded to the buckling of honeycomb cells. The different specimens showed similar load/displacement curves, and the differences observed were only due to the influence of the core density, number of cells, and specimens size on mechanical behavior of hexagonal honeycomb core which has a very important role in the energy absorption capacity. In addition, this study allowed us to build a database of experimental tests for various configurations and allowed us to know the precise energy absorption capacity.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Precipitation of Carbides and Dissolution of Widmanstätten Structure for Enhanced Hardness in Ti{sub 2}AlNb-Based Alloys

Carbide-reinforced Ti{sub 2}AlNb matrix composites were spark plasma sintered at 1100 °C by incorporating CNTs into single-B2-phase Ti-22Al-25Nb powders. The as-SPSed alloys were solution treated and then aged in different phase regions. By kinetics analysis and energy-dispersive spectroscopy, it is found carbon will stabilize α{sub 2} phase during solution treatment, and the formation of carbide results in the Nb-depleted regions, which further induces the formation of curly B2 + O Widmanstätten structure during quenching. Different from the general Widmanstätten structure in the aged Ti{sub 2}AlNb alloy, the remained α{sub 2} will consume the B2 within the Widmanstätten structure, when the carbon-added alloy is aged in B2 + O phase region. Compared to the alloy without CNTs, the Vickers hardness of the aged carbon-added Ti{sub 2}AlNb alloy is increased significantly, which is related to the uniform and abundant columnar carbides within the O-phase matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Influence of Shell Mold Composition on the As-cast Macro- and Micro-structure of Thin-Walled IN713C Superalloy Castings

In the investment casting process, the building of ceramic layers around the wax pattern is the main time-consuming stage. Increasing their number ensures sufficient mechanical properties, but also lengthens the whole process, including drying time and preheating of the mold. Four molds for casting Ni-based superalloy IN713C were strengthened by glass fibers, included in the slurry, and metal powder, of Al, Cu, Fe or Ni, in the coverage. Castings were subjected to microstructural investigations in order to find out if the new design can be promising for the manufacture of jet engine components. Bend tests revealed that the green strengths of all new molds were higher, at least 3.65 MPa, than that of the unmodified molds, 3.0 MPa. Optical microscopy revealed that the composition of a mold had a strong influence on stereological parameters of equiaxed IN713C grains. Microstructural observation and hardness measurements of castings revealed differences in the volume fraction of strengthening phases, porosity and hardness. The microstructure due to the complex chemical composition of IN713C consisted of several phases including ternary eutectics as a consequence of L → γ + Ni{sub 7}Zr{sub 2} + (Nb, Zr)C.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Primary Processing Parameters, Porosity Production, and Fatigue Prediction for Additively Manufactured Alloy 718

Powder bed fusion processes commonly introduce voids and defects into components. It has been shown that many of these features and their size and shape characteristics are controllable through process parameter manipulation, but this process is typically time-consuming and expensive. In spite of this, an experiment was developed to explore a wide region of laser powder bed fusion process space, and several void measurements were obtained to characterize component density percentage, pore size, and pore shape. Then, multiple models commonly used in the literature to predict porosity were examined and compared with the experimental data. Using the developed porosity model, a fatigue life prediction framework was adapted, and the predictions were compared to the previously published experimental data. Results of this investigation reveal the strengths and weaknesses of multiple literature models in predicting porosity, and they depict how porosity and resulting fatigue lives vary across process space.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Effect of Weld Metal Composition on Microstructural and Mechanical Properties of Dissimilar Welds Between Monel 400 and Inconel 600

The current work was carried out to characterize welding of Inconel 600 superalloy and Monel 400. In the present study, gas tungsten arc welding (GTAW) with four types of filler metals (ENiCu, ENiCu-7, ENiCr-3 and ENiCrFe-3) was utilized. The filler metals were categorized into two groups based on the presence of Cr and Nb in their chemical composition. This paper describes the selection and application of welding consumables in manufacturing dissimilar metal combinations. It was found that (Nb/Cr) ratio and Fe content can affect on the size and amount of carbides. During solidification of ENiCr-3 and ENiCrFe-3 filler metals, Nb leaves dendritic cores and is rejected to inter-dendritic regions because of its high tendency for segregation. However, No brittle Laves phase was detected in the welds. The interface between weld metal and base metal and gradual changes in alloying elements were also investigated by scanning electron microscopy. EDX analysis was also applied for different samples. Microhardness measurements and tensile test were performed on the joints. The average hardness value in the weld metal obtained from ENiCrFe-3 is higher than the other welds. ENiCu-7 weld exhibited the highest tensile strength of 540 MPa and percent elongation of 53% in contrast to ENiCrFe-3 weld with the lowest tensile strength (518 MPa) and percent elongation (39%).

36 MATERIALS SCIENCE↗
DOE OSTI2017

Versatile Oxide Films Protect FeCrAl Alloys Under Normal Operation and Accident Conditions in Light Water Power Reactors

The US has currently a fleet of 99 nuclear power light water reactors which generate approximately 20% of the electricity consumed in the country. Near 90% of the reactors are at least 30 years old. There are incentives to make the existing reactors safer by using accident tolerant fuels (ATF). Compared to the standard UO2–zirconium-based system, ATF need to tolerate loss of active cooling in the core for a considerably longer time while maintaining or improving the fuel performance during normal operation conditions. Ferritic iron-chromium-aluminum (FeCrAl) alloys have been identified as an alter-native to replace current zirconium alloys. They contain Fe (base) + 10–22 Cr + 4–6 Al and may contain smaller amounts of other elements such as molybdenum and traces of others. FeCrAl alloys offer outstanding resistance to attack by superheated steam by developing an alumina oxide on the surface in case of a loss of coolant accident like at Fukushima. FeCrAl alloys also perform well under normal operation conditions both in boiling water reactors and pressurized water reactors because they are protected by a thin oxide rich in chromium. Under normal operation condition, the key element is Cr and under accident conditions it is Al.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Techno-Economic Analysis of Magnesium Extraction from Seawater via a Catalyzed Organo-Metathetical Process

Magnesium (Mg) has many useful applications especially in various Mg alloys which can decrease weight while increasing strength. To increase the affordability and minimize environment consequence, a novel catalyzed organo-metathetical (COMET) process was proposed to extract Mg from seawater aiming to achieve significant reduction in total energy and production cost comparing with the melting salt electrolysis method currently adopted by US Mg LLC. A process flowsheet for a reference COMET process was set-up using Aspen Plus which included five key steps, anhydrous MgCl2 production, transmetallation, dibutyl Mg decomposition, n-BuLi regeneration, and LiCL electrolysis. The energy and production cost and CO2 emission were estimated based on the Aspen modeling using Aspen economic analyzer. Our results showed that it is possible to produce Mg from seawater with a production cost of $2.0/kg-Mg while consuming about 35.3 kWh/kg-Mg and releasing 7.0 kg CO2/kg-Mg. A simplified US Mg manufacturing process was also generated using Aspen and the cost and emission results were estimated for comparison purpose. Under our simulation conditions, the reference COMET process maintain a comparable CO2 emission rate and can save about 40% in production cost and save about 15% energy compared to the simplified US Mg process.

Liu, Jian (ORCID:0000000153297408)↗