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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 OSTI2016

X-ray tomography studies on porosity and particle size distribution in cast in-situ Al-Cu-TiB{sub 2} semi-solid forged composites

X-ray computed tomography (XCT) was used to characterise the internal microstructure and clustering behaviour of TiB{sub 2} particles in in-situ processed Al-Cu metal matrix composites prepared by casting method. Forging was used in semi-solid state to reduce the porosity and to uniformly disperse TiB{sub 2} particles in the composite. Quantification of porosity and clustering of TiB{sub 2} particles was evaluated for different forging reductions (30% and 50% reductions) and compared with an as-cast sample using XCT. Results show that the porosity content was decreased by about 40% due to semi-solid forging as compared to the as-cast condition. Further, XCT results show that the 30% forging reduction resulted in greater uniformity in distribution of TiB{sub 2} particles within the composite compared to as-cast and the 50% forge reduction in semi-solid state. These results show that the application of forging in semi-solid state enhances particle distribution and reduces porosity formation in cast in-situ Al-Cu-TiB{sub 2} metal matrix composites. - Highlights: •XCT was used to visualise 3D internal structure of Al-Cu-TiB{sub 2} MMCs. •Al-Cu-TiB{sub 2} MMC was prepared by casting using flux assisted synthesis method. •TiB{sub 2} particles and porosity size distribution were evaluated. •Results show that forging in semi-solid condition decreases the porosity content and improve the particle dispersion in MMCs.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Preparation of Bimetal Objects by Lost Foam Casting

The possibility of obtaining bimetallic steel castings by the lost foam casting method is demonstrated, in which an insert of special steel is placed in an expanded polystyrene mold. Bottom casting is used. With the optimum choice of the casting temperature, fusion of the steels is guaranteed and there is no warping of flat inserts. Stages of bimetallic casting formation are considered and the parameters affecting filling of the mold and ensuring the production of a finished casting are determined. It is shown that the heat treatment of objects with air cooling provides hardness of 20–46 HRC for steel of 20X13 with different tempering conditions. The technology is recommended for parts of the locking assembly of pipeline fittings and other products where a combination of local special properties and workability is required.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Feasibility Study of Continuous Casting of Steel Billets in Twin-Belt Caster

Integrated casting and rolling in a series production line is well established for the non-ferrous metals through the use of twin-belt casting technology. However, this twin-belt casting with high mass flow is not yet commercialized in the continuous production of steel alloys. A novel steel casting for the in-line rolling (named LUUP method) is presented and one main focus of this work is to design a casting machine: twin-belt caster. Influence of mass flow rate and dimensional ratio on the solidification, compensation, and total process length is addressed. A gap-dependent belt and dam block side heat transfer is modeled. The admissible casting speed due to the limitations of caster length and shell strength is addressed. The total process length only depends on the mass flow rate. A 2D traveling slice numerical model is presented with realistic boundary conditions for the entire process starting from the meniscus to roll mill entry.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Quantitative Evaluations of Surface Cleanliness in IF Steel Slabs at Unsteady Casting

Macro-inclusions in the surface layer of slabs are mainly responsible for the sliver defects in IF steel sheets. In the present work, macro-inclusions in six kinds of unsteady cast IF steel slabs involving four unsteady states (casting start, ladle change, nozzle change and casting end) in one casting sequence were quantitatively characterized using an automatic inclusion analyzer with a total detection area of 238,048 mm{sup 2}. The cleanliness of corresponding normal slabs was also evaluated as the benchmark study, and the number density (ND) of inclusions > 50 µm was used to describe the surface slab cleanliness. Generally, alumina-based and mold powder inclusions were detected, and the former type was further subdivided into alumina clusters, alumina associated with bubbles, refractory-related alumina, Al-Ti complex oxides and CaO-Al{sub 2}O{sub 3}-MgO. Several large-sized alumina-based inclusions were detected in the normal slabs with an average ND of 0.31 N/cm{sup 2}, although they had very low total oxygen (TO) contents (10~13 ppm). No mold powder inclusions were found in normal slabs. For all the unsteady slabs, alumina-based and mold powder inclusions were both observed, and the percentage of the former kind was ≥ 90 pct. The average density of macro-inclusions for the first slab was 1.621 N/cm{sup 2}, whose cleanliness was much worse than any of the other unsteady slabs. The first slab should be downgraded. For the second slab, the ND of macro-inclusions was 0.385 N/cm{sup 2}, which was still larger than the normal slabs because of the lasting effect of the re-oxidation. For the penultimate, cap-off and SEN changed slabs, the density of macro-inclusions fluctuated from 0.25~0.35 N/cm{sup 2}, which was close to the average level of normal slabs. However, mold flux-originated inclusions were frequently observed in these slabs because of flow pattern variations due to the casting speed change. In terms of the slab during the ladle change process, mold powder inclusions were frequently detected even though the casting speed remained constant. A mold powder entrapment mechanism was proposed, which showed the entrapment occurred owing to the flow pattern change induced by forming/dropping of SEN clogs due to re-oxidation by FeO in the ladle slag and tundish steel temperature variations during the ladle change practice. The severity of powder entrapment and re-oxidation was also given for different kinds of unsteady slabs, which provides a direct guide to treating these slabs in the steel plant.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Development of cast alumina-forming austenitic stainless steels

Cast Fe-Ni-Cr chromia-forming austenitic stainless steels with Ni levels up to 45 wt. % are used at high temperatures in a wide range of industrial applications that demand microstructural stability, corrosion resistance, and creep strength. Although alumina scales offer better corrosion protection at these temperatures, designing cast austenitic alloys that form a stable alumina scale and achieve creep strength comparable to existing cast chromia-forming alloys is challenging. This work outlines the development of cast Fe-Ni-Cr-Al austenitic stainless steels containing about 25 wt. % Ni with good creep strength and the ability to form a protective alumina scale for use at temperatures up to 800 C - 850 C in H 2 O-, S-, and C- containing environments. Creep properties of the best alloy were comparable to that of HK-type cast chromia-forming alloy along with improved oxidation resistance typical of alumina-forming alloys. Lastly, challenges in the design of cast alloys and a potential path to increasing the temperature capability are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microstructures of ancient and modern cast silver–copper alloys

The microstructures of modern cast Sterling silver and of cast silver objects about 2500 years old have been compared using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy dispersive X-ray microanalysis (EDX) and electron backscatter diffraction (EBSD). Microstructures of both ancient and modern alloys were typified by silver-rich dendrites with a few pools of eutectic and occasional cuprite particles with an oxidised rim on the outer surface. EBSD showed the dendrites to have a complex internal structure, often involving extensive twinning. There was copious intragranular precipitation within the dendrites, in the form of very fine copper-rich rods which TEM, X-ray diffraction (XRD), SEM and STEM suggest to be of a metastable face-centred-cubic (FCC) phase with a cube–cube orientation relationship to the silver-rich matrix but a higher silver content than the copper-rich β in the eutectic. Samples from ancient objects displayed a wider range of microstructures including a fine scale interpenetration of the adjoining grains not seen in the modern material. Although this study found no unambiguous evidence that this resulted from microstructural change produced over archaeological time, the copper supersaturation remaining after intragranular precipitation suggests that such changes, previously proposed for wrought and annealed material, may indeed occur in ancient silver castings. - Highlights: • Similar twinned structures and oxidised surfaces seen in ancient and modern cast silver • General precipitation of fine Cu-rich rods apparently formed by discontinuous precipitation is characteristic of as-cast silver. • The fine rods are cube-cube related to the matrix in contrast with the eutectic. • The silver-rich phase remains supersaturated with copper. • Possibly age-related grain boundary features seen in ancient cast silver.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Development in corrosion resistance by microstructural refinement in Zr-16 SS 304 alloy using suction casting technique

Highlights: • Grain refinement was made in Zr–16 wt.% SS alloy while prepared by suction casting process. • Distribution of Laves phase, e.g., Zr{sub 2}(Fe, Cr) was raised in suction cast (SC) Zr–16 wt.% SS. • Corrosion resistance was improved in SC alloy compared to that of arc-melt-cast alloy. • Grain refinement in SC alloy assisted for an increase in its corrosion resistance. - Abstract: Zirconium (Zr)-stainless steel (SS) hybrid alloys are being considered as baseline alloys for developing metallic-waste-form (MWF) with the motivation of disposing of Zr and SS base nuclear metallic wastes. Zr–16 wt.% SS, a MWF alloy optimized from previous studies, exhibit significant grain refinement and changes in phase assemblages (soft phase: Zr{sub 2}(Fe, Cr)/α-Zr vs. hard phase: Zr{sub 3}(Fe, Ni)) when prepared by suction casting (SC) technique in comparison to arc-cast-melt (AMC) route. Variation in Cr-distribution among different phases are found to be low in suction cast alloy, which along with grain refinement restricted Cr-depletion at the Zr{sub 2}(Fe, Cr)/Zr interfaces, prone to localized attack. Hence, SC alloy, compared to AMC alloy, showed lower current density, higher potential at the breakdown of passivity and higher corrosion potential during polarization experiments (carried out under possible geological repository environments, viz., pH 8, 5 and 1) indicating its superior corrosion resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Technetium Getters to Improve Cast Stone Performance

The cementitious material known as Cast Stone has been selected as the preferred waste form for solidification of aqueous secondary liquid effluents from the Hanford Tank Waste Treatment and Immobilization Plant (WTP) process condensates and low-activity waste (LAW) melter off-gas caustic scrubber effluents. Cast Stone is also being evaluated as a supplemental immobilization technology to provide the necessary LAW treatment capacity to complete the Hanford tank waste cleanup mission in a timely and cost effective manner. Two radionuclides of particular concern in these waste streams are technetium-99 (99Tc) and iodine-129 (129I). These radioactive tank waste components contribute the most to the environmental impacts associated with the cleanup of the Hanford site. A recent environmental assessment of Cast Stone performance, which assumes a diffusion controlled release of contaminants from the waste form, calculates groundwater in excess of the allowable maximum permissible concentrations for both contaminants. There is, therefore, a need and an opportunity to improve the retention of both 99Tc and 129I in Cast Stone. One method to improve the performance of Cast Stone is through the addition of “getters” that selectively sequester Tc and I, therefore reducing their diffusion out of Cast Stone. In this paper, we present results of Tc and I removal from solution with various getters with batch sorption experiments conducted in deionized water (DIW) and a highly caustic 7.8 M Na Ave LAW simulant. In general, the data show that the selected getters are effective in DIW but their performance is comprised when experiments are performed with the 7.8 M Na Ave LAW simulant. Reasons for the mitigated performance in the LAW simulant may be due to competition with Cr present in the 7.8 M Na Ave LAW simulant and to a pH effect.

Cast Stone↗
DOE OSTI2018

Computational Design and Development of a New, Lightweight Cast Alloy for Advanced Cylinder Heads in High-Efficiency, Light-duty Engines

The objective of the collaborative multi-year Cast Lightweight Alloy program was to develop a new, lightweight, cast aluminum alloy for automotive engines with better high temperature properties than the incumbent alloys (B319, A356, A356+0.5Cu) to allow for more efficient engine operation. The program kicked off with the generation of alloy concepts and selecting alloy models with specific milestones for establishing property requirements, generating design concepts and selecting models for casting design. Following this, sub-scale prototypes of the promising design concepts were cast and characterized in order to validate the design concepts and develop data for subsequent model calibration and improvement. Using the calibrated models, a set of alloy designs were created. This first generation set of designs were validated through production and characterization of lab-scale castings. With the learnings from the lab-scale prototypes and the improvements in the computational models, final embodiment design of the new alloy was completed. The final alloy designs were cast at lab-scale and also at component-scale to characterize its final properties. An alloy recyclability analysis and cost modelling was also performed.

36 MATERIALS SCIENCE↗
DOE OSTI2017

The Prediction of Long-Term Thermal Aging in Cast Austenitic Stainless Steel

Cast austenitic stainless steel (CASS) materials are extensively used for many massive primary coolant system components of light water reactors (LWRs) including coolant piping, valve bodies, pump casings, and piping elbows. Many of these components are operated in complex and persistently damaging environments of elevated temperature, high pressure, corrosive environment, and sometimes radiation for long periods of time. Since a large number of CASS components are installed in every nuclear power plant and replacing such massive components is prohibitively expensive, any significant degradation in mechanical properties that affects structural integrity, cracking resistance in particular, of CASS components will raise a serious concern on the performance of entire power plant. The CASS materials for nuclear components are highly corrosion-resistant Fe-Cr-Ni alloys with 300 series stainless steel compositions and mostly austenite (γ)–ferrite (δ) duplex structures, which result from the casting processes consisting of alloy melting and pouring or injecting liquid metal into a static or spinning mold. Although the commonly used static and centrifugal casting processes enable the fabrication of massive components with proper resistance to environmental attacks, the alloying and microstructural conditions are not highly controllable in actual fabrication, especially in the casting processes of massive components. In the corrosion-resistant Fe-Cr-Ni alloy system, the minor phase (i.e., the δ-ferrite phase) is inevitably formed during the casting process, and is in a non-equilibrium state subject to detrimental changes during exposure to elevated temperature and/or radiation. In general, relatively few critical degradation modes are expected within the current design lifetime of 40 years, given that the CASS components have been processed properly. It has been well known, however, that both the thermal aging and the neutron irradiation can cause degradation of static and impact toughness in the cast stainless steels, and if combined with any flaws formed during the fabrication process or in service, the thermal degradation in CASS components can be a serious concern for the integrity of the power plant. On the integrity of the CASS components during the extended lifetime of 60 years or longer, no conclusive prediction has been possible, primarily because no direct experience with these materials currently exists, and the aging behavior of CASS alloys still remains largely uncertain. The ongoing research for CASS aging, as part of the LWRS Program/Materials Aging and Degradation Pathway, is an integrated research using holistic experimental and modeling means to provide both the scientific understanding on the aging and failure phenomena and the practical models to predict the degree of property degradation.

cast stainless steels↗
DOE OSTI2019

Measurement of Residual Strain in the Cylinder Bridge of High-Pressure Die Cast A383 Engine Blocks Using Neutron Diffraction

This article describes the use of neutron diffraction to measure residual strains in high-pressure die cast aluminum alloy engine blocks. High-pressure die casting is widely used to manufacture aluminum alloy components for automobile applications such as engine blocks. Thermal gradients during this process can generate residual strain and stresses and may cause premature failure during service. Neutron diffraction can be used to measure the residual stress distributions deep inside large castings, as neutrons have much larger penetrating power than X-rays. In this work, neutron diffraction was used to measure the residual strain (in the axial and hoop directions) in the cylinder bridge region of high-pressure die cast A383 engine blocks in as-cast and heat-treated conditions. The results suggest that the residual strain in the cylinder bridge is tensile in both the axial and hoop components for both as-cast and heat-treated engines. The residual strain in hoop direction is higher than the strain in axial direction. Residual strain in axial and hoop directions is relaxed after heat treatment.

Liu, Tao↗
DOE OSTI2020

Neutron Diffraction Analysis of Residual Strain in High-Pressure Die Cast A383 Engine Blocks

The residual strains in three high-pressure die cast A383 engine blocks were measured using neutron diffraction. Residual strains and stresses can be generated during high-pressure die casting process due to high thermal gradients and may cause fatigue failure or dimensional distortion. Neutron diffraction can measure the residual strain distributions deep inside castings with complex geometries, because neutrons can penetrate substantially more material than x-rays. In this paper, the residual strains (in the axial and hoop directions) along the whole cylinder bridge of high-pressure die cast A383 engine blocks in as-cast and heat-treated conditions were measured by neutron diffraction methods. The effect of heat treatment on the distribution and magnitude of residual strains was also investigated. The results indicate that the residual strain in the cylinder bridge is tensile in both the axial and hoop components for both the as-cast and the heat-treated engine blocks. The residual strain in the hoop direction is bigger in magnitude than the residual strain in the axial direction. Heat treatment significantly relaxes the residual strain in the axial direction but only slightly relaxes the residual strain in the hoop direction.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Investigating the failure behavior of cast Al-11Ce-0.4Mg alloys using in-situ scanning electron microscopy tensile testing

Within the last decade, research on Al-Ce-Mg alloys has reported promising results for use in cast part applications. In this paper, the failure behavior of cast Al-11Ce-0.4Mg (wt%) was investigated experimentally with focus on the effect the matrix and intermetallic phases have on the fracture propagation behavior at failure. For the first time, in-situ SEM tensile testing was used to study the failure behavior of cast Al-Ce alloys, reporting results for uniaxial, DIC, and single edge notch tensile tests. The results of the in-situ SEM tensile testing were compared with the materials characterization experiments, which included serial sectioning, EBSD, EDS, and fractography. Analysis of EBSD and EDS mapping of cast Al-11Ce-0.4Mg showed that the cast microstructure was a hypereutectic two phase Al-Ce alloy with grains encompassing large complex colonies of laminar eutectic Al 11 Ce 3 intermetallic. The uniaxial tensile results reported the effect casting defects have on the strength and ductility of the alloy, and DIC in-situ testing showed that the eutectic colonies plastically deform less than the matrix phase. In-situ SEM single edge notch tensile testing displayed how the strength of an individual phase affected the crack propagation direction in the alloy. The results of both the materials characterization and in-situ tensile testing experiments on the failure of this alloy revealed further directions for future alloy development that can improve both the strength and fracture toughness of Al-Ce-Mg alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2019

An Instrumented Uranium Hemispherical Casting

This work describes an instrumented uranium casting experiment and the analysis of the results. The casting is a hemisphere with inner radius of 75 mm and wall thickness of 10 mm. Casting was performed in a multi-coil vacuum induction melting (VIM) furnace with separate induction power supplies for each coil. One coil was used to heat the crucible and melt the charge material. The second coil was used to heat the top of the mold in order to preheat the mold and obtain the desired initial mold temperature. The current, voltage, and frequency of the mold coil was measured during mold heating. The mold filling rate was measured by a load cell was placed under the mold stack. The thermal history of the casting was measured by 7 thermocouples in the casting cavity and 22 thermocouples imbedded in the graphite mold. Contact pins were also located in the mold to attempt to measure gap formation in the metal-mold interface. This instrumentation provides an in-depth thermal history of the mold heat-up, mold filling, solidification, and cool down. The thermocouples were positioned to allow for the casting/mold interfacial heat transfer coefficient to be determined as a function of position and time. The casting was sectioned and metallography and chemical analysis was performed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Microwave Cast Material Examination

Microwave-cast material dating from the latest prototype development period and subsequent TRL 7 advancement testing was sent to LANL for additional characterization. The initial characterization described here is considered a supplement to and verification of that performed by Y-12 during the Technology Readiness Assessment process. The carbon chemistry results from Y-12 and LANL regarding early prototype microwave cast test object (CTO) and cylinder castings match within expectations. Only one fully intact as-cast CTO was available for examination in which carbon chemistry does not appear to vary spatially, at least at relatively low carbon levels (hypoeutectic). The large as-cast grain size leads to relatively poor grain size statistics and similar difficulties were encountered during the TRA. Small, isolated gas pores were observed in four of the five metallographic samples in prototype CTO casting PT-01. Finally, the next phase of characterization work, which focuses on corrosion behavior, has started and is described briefly.

36 MATERIALS SCIENCE↗
NASA NTRS1982

The effects of weld-repair and hot isostatic pressing on the fracture properties of Ti-5Al-2.5Sn ELI castings

The Ti-5Al-2.5Sn extremely low interstitial alloy employed in the large castings which form the critical attachment fittings of the Space Shuttle External Tank was selected because of its high fracture resistance at cryogenic temperatures. Casting was selected over alternative fabrication methods because of its lower cost and adaptability to design changes, although it was found necessary to weld-repair surface and subsurface casting defects in order to reduce the scrap rate and maintain the inherent cost advantage of the castings. Hot Isostatic Pressing was experimentally found to heal the surface and internal defects of the castings, but did not improve tensile or fracture properties and was therefore rejected as a production technique. Production castings are instead weld-repaired, without any mechanical property degradation.

Misra, M. S.↗
NASA NTRS1989

High density tape casting system

A system is provided for casting thin sheets (or tapes) of particles bound together, that are used for oxygen membranes and other applications, which enables the particles to be cast at a high packing density in a tape of uniform thickness. A slurry contains the particles, a binder, and a solvent, and is cast against the inside walls of a rotating chamber. Prior to spraying the slurry against the chamber walls, a solvent is applied to a container. The solvent evaporates to saturate the chamber with solvent vapor. Only then is the slurry cast. As a result, the slurry remains fluid long enough to spread evenly over the casting surface formed by the chamber, and for the slurry particles to become densely packed. Only then is the chamber vented to remove solvent, so the slurry can dry. The major novel feature is applying solvent vapor to a rotating chamber before casting slurry against the chamber walls.

Collins, Earl R., Jr.↗
NASA NTRS2001

A Winning Cast

Howmet Research Corporation was the first to commercialize an innovative cast metal technology developed at Auburn University, Auburn, Alabama. With funding assistance from NASA's Marshall Space Flight Center, Auburn University's Solidification Design Center (a NASA Commercial Space Center), developed accurate nickel-based superalloy data for casting molten metals. Through a contract agreement, Howmet used the data to develop computer model predictions of molten metals and molding materials in cast metal manufacturing. Howmet Metal Mold (HMM), part of Howmet Corporation Specialty Products, of Whitehall, Michigan, utilizes metal molds to manufacture net shape castings in various alloys and amorphous metal (metallic glass). By implementing the thermophysical property data from by Auburn researchers, Howmet employs its newly developed computer model predictions to offer customers high-quality, low-cost, products with significantly improved mechanical properties. Components fabricated with this new process replace components originally made from forgings or billet. Compared with products manufactured through traditional casting methods, Howmet's computer-modeled castings come out on top.

Source record↗