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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Accounting for Melt Flow Pattern and Solid Fraction Evolution in DC Casting of Al-Cu Alloy Using v{sup 2}−f Turbulence Model

Experimental techniques remain reliable approaches for investigating the effects of parameters of the direct chill (DC) casting process on macrosegregation, grain structure formation, and surface quality. However, experimental analysis methods of these effects are expensive and can often prove difficult to implement. Understanding of the complex physics of the solidification process remains limited, and this makes it indispensable to use accurate numerical modeling tools as a complement to experiments. Numerical modeling without consideration of turbulent flow is unsuitable for application to solidification occurring during DC casting, since significant turbulent flow exists in the upper section of the cast, where the liquid pool exists. The present work employed a low-Re v{sup 2}−f turbulence model and a dual-zone solidification flow model to predict the melt flow pattern, turbulence level, sump depth, transition zone thickness, and mushy zone thickness in the DC casting of Al-Cu alloy. The obtained results provided evidence of significant damping of the flow in the slurry zone. Furthermore, results of different simulation cases revealed a narrower transition zone and shallower sump.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Optimized Gating System for Steel Castings

Computer modeling using a commercially available software package was used to explore the optimization of filling systems based on the relatively new concepts of avoiding entrainment of air bubbles and oxides by avoiding surface turbulence. The test casting was based on a pattern for a traditional top poured test bar, whose cross section was a tri-lobed clover-like shape. The study illustrates clearly that the detailed design of the filling system has a major influence on the conditions for defect generation during filling. Traditional steel casting systems using the widely popular assembly of preformed refractory tubes were found to behave poorly. Systems were demonstrated which were capable of delivering highly controlled filling behavior. The latest systems to be developed employed (1) a naturally pressurized filling system and (2) the use of filters placed flush on the top of the runner to act as bubble diverters, together with (3) terminal spin traps. These novel filling systems demonstrated excellent performance in simulation, in agreement with practical experience of the capability (of the trident gate in particular) to produce, for the first time in the history of casting, defect-free castings on a routine basis.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Gating System Design Optimization for Investment Casting Process

This article aims to optimize specific castings, characterized as an element of the continuous track for armored vehicle. During the primary melts, defects in the form of oxide films and shrinkage porosity occurred. Steel 20ChGSNM described by the Russian GOST standard was used as a batch material, and the investment casting method was selected for production. To eliminate the above-mentioned defects, only changes in the gating system were allowed, because the interference with an ongoing production regarding technical and technological parameters was unacceptable by the manufacturer. Numerical simulation, x-ray, macro-structural and micro-structural analysis were used during the optimization process. The three variants were analyzed, and the achieved results demonstrated that it is possible to significantly affect the casting internal homogeneity by modifying the gating system individual parts. The final variant ensured a decrease in defects by up to 90% and the production of casting having the quality required by the customer.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Development of a Squeeze Semisolid High-Pressure Die Casting Process for Magnesium Structural Parts

High-pressure die casting is the most common method used to produce magnesium castings, due to the excellent balance of cost and properties for high production volumes with limitations in terms of final mechanical properties. A newly developed process based on employing low injection speeds, in a range slightly over the standard semisolid speeds with a modified die, with thick gates and high die temperatures has been developed. Despite working with speeds that are not in the lamellar flow, the obtained parts present very low porosity, allowing the use thermal treatments to increase the ductility without producing blisters. The demonstration has been performed in a AM60B magnesium body joint produced by the squeeze casting process. Finally, the microstructure and the mechanical properties of as-cast and T4 heat-treated samples were studied. The results indicate the improvement of the mechanical properties in T4 heat-treated parts; specifically, a 40% improved deformation-to-failure, 40-60% improved penetration force and 90% of energy absorption were possible to obtain employing the newly developed SC + T4 process.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Transition Layer on Bending Resistance in Copper-Clad Aluminum Composite Casting

The performance of the transition layer in a Cu/Al composite casting directly affects the quality of subsequent plastic deformation processing; however, there are no universal or standardized measurement indices for the performance of the transition layer. In this study, Cu/Al composite castings were prepared using the pouring aluminum method, and the resulting solidification microstructures on the bending resistance were investigated. The results of this study lay a theoretical foundation for the development of the plastic processing technologies of these composite castings. A thinner transition layer in the Cu/Al composite casting led to improved bending resistance. In addition, for a fixed total thickness of the transition layer, the bending resistance was mainly controlled by the γ/β interface and β + eutectic (α + β) microstructure, and the thickness of the γ phase had a negligible effect on the bending resistance. The γ/β interface cracked first when the transition layer bore the tensile and shear stress during the bending process, which resulted in the transition layer easily separating from the copper. The bending resistance of the transition layer can be feasibly judged by measuring the bending angle of the specimen tip, which can be easily performed when the specimen bends toward the aluminum direction, suggesting that our proposed method has considerable practical significance.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Effect of Casting Speed on Microstructure, Microsegregation, and Mechanical Properties of High-Strength Mg-Nd-Zn-Zr Alloy

High-quality Mg-Nd-Zn-Zr magnesium alloy billets were successfully prepared by direct chill casting. The effect of casting speed on microstructure, microsegregation, and mechanical properties of the Mg-Nd-Zn-Zr alloy was systematically investigated. The results show that the as-cast microstructure is composed of equiaxed α-Mg and Mg{sub 12}Nd. Optimum values of mechanical properties were obtained corresponding to the casting speed of 90 mm/min. An age hardening at 200 °C took a remarkable effect on the mechanical properties of billets. The maximum ultimate tensile strength ~ 323.4 MPa was obtained in the billet undergoing T6 heat treatment. The shapes of concentration curves of various alloying elements (e.g., Nd and Zn) in Mg-Nd-Zn-Zr, as predicted by the Gulliver–Scheil model, resemble reasonably with the shapes measured by electron probe microanalysis.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Properties of a thick-section narrow-gap gas tungsten arc weld of cast Haynes 282

Abstract A 50.8-mm-deep gas tungsten arc weld was made with matching filler metal in cast Haynes 282 alloy. The narrow-gap joint was filled with 104 weld beads. Visual and dye-penetrant inspection of cross-weld specimens indicated that the cast base metal contained numerous casting defects. No visible indications of physical defects were found in the weld deposit. The weld heat-affected zone was characterized by microcracking and localized recrystallization. The cause of the cracking could not be determined. Hardness testing showed that a softened region in the as-welded heat-affected zone was nearly eliminated by post-weld heat treatment. Tensile testing up to 816 °C showed that cross-weld specimen strengths ranged from 57 to 79% of the cast base metal tensile strength. The stress-rupture strengths of cross-weld specimens are within 20% of base metal reference data. Failures of both tensile and stress-rupture specimens occurred in the base metal.

282↗
DOE OSTI2022

Property-structure-process relationships in dissimilar material repair with directed energy deposition: Repairing gray cast iron using stainless steel 316L

Directed energy deposition (DED) based remanufacturing leverages the flexibility of additive manufacturing to add value to broken or worn components. DED offers the ability to repair cast iron, a material difficult to repair with traditional welding techniques. Despite this, development of appropriate DED process conditions for bimetallic cast iron structures lags low- and medium-carbon steel repair. Thermal stresses and porosity generated by high-temperature deposition on cast iron often lower mechanical properties and hinder the qualification process. In this report scanning speed, powder mass flow rate, and stepover width are studied in multiple-track structures deposited on gray cast iron. Dilution and residual stresses are found to be highly dependent on the selected process parameters. Samples with a higher volumetric energy input, e.g., slower scanning speeds and higher powder feed rates, showed improved density and lower residual stresses but suffered lower dilution into the substrate. The presented conditions further the development of additive manufacturing technologies for automotive repair.

42 ENGINEERING↗
DOE OSTI2014

Characterization of microstructure, texture and magnetic properties in twin-roll casting high silicon non-oriented electrical steel

An Fe-6.5 wt.% Si-0.3 wt.% Al as-cast sheet was produced by twin-roll strip casting process, then treated with hot rolling, warm rolling and annealing. A detailed study of the microstructure and texture evolution at different processing stages was carried out by optical microscopy, X-ray diffraction and electron backscattered diffraction analysis. The initial as-cast strip showed strong columnar grains and pronounced < 001 >//ND texture. The hot rolled and warm rolled sheets were characterized by large amounts of shear bands distributed through the thickness together with strong < 110 >//RD texture and weak < 111 >//ND texture. After annealing, detrimental < 111 >//ND texture almost disappeared while beneficial (001)<210 >, (001)<010 >, (115)<5 − 10 1 > and (410) < 001 > recrystallization textures were formed, thus the magnetic induction of the annealed sheet was significantly improved. The recrystallization texture in the present study could be explained by preferred nucleation and grain growth mechanism. - Highlights: • A high silicon as-cast strip with columnar structure was produced. • A thin warm rolled sheet without large edge cracks was obtained. • Microstructure and texture evolution at each stage were investigated. • Beneficial (001)<210 >, (001)<010 >, (410)<001 > recrystallization textures were formed. • The magnetic induction of annealed sheet was significantly improved.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Synthesis and structural evaluation of freeze-cast porous alumina

In this work we fabricated alumina samples by the freeze-casting technique using tert-butanol as the solvent. The prepared materials were examined by scanning electron microscopy and X-ray microtomography. Next, they were coated with sol–gel silica films by dip-coating. Permeability tests were carried out in order to assess the permeation behavior of the materials processed in this study. We observed that the sintering time and alumina loading showed a remarkable effect on both the structural properties and flexural strength of the freeze-cast samples. Nitrogen adsorption tests revealed that the silica prepared in this study exhibited a microporous structure. It was observed that the presence of silica coatings on the alumina surface decreased the CO{sub 2} permeance by about one order of magnitude. Because of the similar kinetic diameters of nitrogen and carbon dioxide, the CO{sub 2}/N{sub 2} system showed a separation efficiency that was lower than that observed for the He/CO{sub 2} and He/N{sub 2} systems. We noticed that increasing the feed pressure improved the separation capacity of the obtained materials. - Highlights: • Porous alumina samples obtained by the freeze-casting technique • Microporous silica coating prepared by a simple sol–gel dip-coating methodology • Samples examined by SEM, μ-CT, and nitrogen sorption tests • Mechanical tests were carried out in the freeze-cast samples. • The presence of silica coatings on the alumina surface decreased the CO{sub 2} permeance.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure characterisation and mechanical properties of a functionally-graded NbC/high chromium white cast iron composite

Highlights: • A functionally-graded NbC – white cast iron composite was centrifugally cast. • Primary NbC particle distribution follows Stokes' Law, with 30 vol% at the surface. • Presence of primary NbC particles refined eutectic M{sub 7}C{sub 3} morphology at the surface. • The surface layer was hard and wear resistant, while the interior was tougher. • NbC and M{sub 7}C{sub 3} carbides form independent eutectic structures within the interior. - Abstract: A functionally graded NbC – high chromium white cast iron composite was successfully fabricated by centrifugal casting for high wear applications. The migration of primary NbC particles to the outer periphery, as predicted by Stokes' law, resulted in an extremely hard outer layer at the surface of a softer bulk material. Microstructural characterisation showed that both the volume fraction and the morphology of the carbides varies along the thickness of the specimen. At the outer surface, the NbC was present as primary carbides while Chinese-script NbC was found in the bulk of the material. Hardness, sliding wear and three-point bending tests confirmed that the outer layer was harder and more wear resistant than the rest of the material, which was correspondingly tougher. The study of the fracture surface of the specimens showed that there is a strong bond between NbC and the matrix such that delamination between the reinforcements and the matrix did not occur during fracture. If Chinese-script NbC can be reduced or prevented in the bulk material, further improvements to toughness could be achieved.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Residual stress in spin-cast polyurethane thin films

Residual stress is inevitable during spin-casting. Herein, we report a straightforward method to evaluate the residual stress in as-cast polyurethane thin films using area shrinkage measurement of films in floating state, which shows that the residual stress is independent of radial location on the substrate and decreased with decreasing film thickness below a critical value. We demonstrate that the residual stress is developed due to the solvent evaporation after vitrification during spin-casting and the polymer chains in thin films may undergo vitrification at an increased concentration. The buildup of residual stress in spin-cast polymer films provides an insight into the size effects on the nature of polymer thin films.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Report on results of current and future metal casting

New modeling capabilities needed to simulate the casting of metallic fuels are added to Truchas code. In this report we summarize improvements we made in FY2015 in three areas; (1) Analysis of new casting experiments conducted with BCS and EFL designs, (2) the simulation of INL’s U-Zr casting experiments with Flow3D computer program, (3) the implementation of surface tension model into Truchas for unstructured mesh required to run U-Zr casting.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2017

Improved Casting Furnace Conceptual Design

In an attempt to ensure more consistent casting results and remove some schedule variance associated with casting, an improved casting furnace concept has been developed. The improved furnace uses the existing arc melter hardware and glovebox utilities. The furnace concept was designed around physical and operational requirements such as; a charge sized of less than 30 grams, high heating rates and minimal additional footprint. The conceptual model is shown in the report as well as a summary of how the requirements were met.

42 ENGINEERING↗
DOE OSTI2019

Manufacture of Wear-Resistant Cast-Iron Grinding Balls without Shrinkage Defects

A manufacturing technology has been developed for wear-resistant cast-iron grinding balls without shrinkage defects. In this method, the balls are cast in single-use sand–clay molds. A new approach to designing the casting system is developed. By numerical modeling, the time dependence of solidification is derived. As a trial, grinding balls are produced by the proposed technology.

42 ENGINEERING↗
DOE OSTI2019

Measurement of heat flow through cast slabs of calcium sulfate dihydrate

Slabs of cast calcium sulfate dihydrate have been used for decades as a heat transfer barrier in commercial and residential construction and are assessed in accordance with the parameters defined by ASTM C1396. The study described herein hypothesizes that minor impurities have significant effects on the high–temperature performance of these casts. Five thermocouples are cast into a 20–mm–thick slab at approximately 4–mm intervals are measured between ambient and approximately 1000°C in a furnace. Thermal diffusivity and inertia are estimated from this temperature profile. This study compares natural, flue gas desulfurized (FGD) and reagent grade hemihydrates that have been converted into the dihydrate form with distilled water; the common additives kaolin and borax are used to modify the cast. The thermocouple data allow an effective thermal diffusivity (α') and an effective thermal inertia (I') to be calculated. Furthermore, the hemihydrate source and kaolin content are found to affect the high–temperature performance; the FGD source increases the thermal inertia, and kaolin inhibits the formation of other borate compounds through intercalation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

First results of the CAST-RADES haloscope search for axions at 34.67 μ eV

We present results of the Relic Axion Dark-Matter Exploratory Setup (RADES), a detector which is part of the CERN Axion Solar Telescope (CAST), searching for axion dark matter in the 34.67 μeV mass range. A radio frequency cavity consisting of 5 sub-cavities coupled by inductive irises took physics data inside the CAST dipole magnet for the first time using this filter-like haloscope geometry. An exclusion limit with a 95% credibility level on the axion-photon coupling constant of g aγ ≳ 4 × 10 -13 GeV -1 over a mass range of 34.6738 μeV < m a < 34.6771 μeV is set. This constitutes a significant improvement over the current strongest limit set by CAST at this mass and is at the same time one of the most sensitive direct searches for an axion dark matter candidate above the mass of 25 μeV. The results also demonstrate the feasibility of exploring a wider mass range around the value probed by CAST-RADES in this work using similar coherent resonant cavities.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Microstructural refinement in ultrasonically modified A356 aluminum castings

Two A356 aluminum alloys (Al-Si-Mg), one with 0.09 wt.% Fe and one with 0.91 wt.% Fe, were cast in a graphite mold with the simultaneous application of local ultrasonic intensification to refine the as-cast microstructure. Ultrasonication during casting transformed the morphology of primary Al grains from dendritic (~140-290 microns in size) to globular (~33-36 microns in size). The alloy with high Fe exhibited globular grains at distances up to 45 mm away from the ultrasound probe, while the alloy with low Fe exhibited globular grains at distances only up to 6 mm away from the ultrasound probe. Near the location of the ultrasound probe (< 2 mm away), a second non-dendritic microstructural morphology was observed with fine aluminum grains (~9-25 microns in size). This unique fine-grained morphology has not been previously reported, contains a greater concentration of Si relative to the globular microstructure, and may be a large, fully eutectic region. Ultrasonication during casting also transformed the morphology of the ß-Al 5 FeSi phase particles (which are deleterious to the strength and ductility of the alloy) in the high Fe alloy from needle-like to rectangular, which could enable the greater use of secondary Al alloys. Thermodynamic simulations conducted to calculate the solidification paths of the two alloys studied predict that the ß-Al 5 FeSi phase begins to form earlier in the alloy with high Fe. Finally, data suggest that the ß-Al 5 FeSi phase (which is more abundant in alloys with high Fe content) may enhance ultrasonically-induced grain refinement.

36 MATERIALS SCIENCE↗