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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Investigation of Skull Formation in a Blast Furnace Hearth

A stable skull layer formed on the inner surface of the hearth could effectively protect the lining and extend blast furnace campaign life. Our first comprehensive work of using integrated heat transfer, fluid flow dynamics and solidification numerical simulation to investigate skull formation phenomena in a blast furnace hearth is presented here. The impact of hearth design and furnace operation parameters on skull formation is examined, including lining property and structure, cooling water temperature and flow rate, hot metal production rate, temperature and viscosity, and cast practice. Our findings are compared with operating experience of United States Steel blast furnaces.

42 ENGINEERING↗
DOE OSTI2023

Improving the Mechanical Properties of Cast Aluminum Via Ultrasonication-Induced Microstructural Refinement

One barrier to the broader use of cast aluminum alloys in automotive applications is their poor mechanical properties, especially compared to wrought materials. This study investigates the use of ultrasound to refine the microstructure of cast aluminum alloys during solidification and thus improve their mechanical properties. An A356 aluminum alloy (Al-Si-Mg) with added Fe (to mimic a recycle-grade alloy) was cast in a graphite mold with the simultaneous application of ultrasound. Tensile specimens were extracted from the castings and heat treated to a T6 temper. Ultrasonication during casting transformed the morphology of primary aluminum grains from dendritic (~140 microns in size) to globular (~36 microns in size), increased the ultimate tensile strength by 10 %, and tripled the ductility compared to casting without ultrasound. This improvement in strength and ductility demonstrates the potential for ultrasonic processing to improve the performance of cast aluminum alloys without altering their chemistry or additional post-processing.

Aluminum, Solidification, Ultrasound, Grain refinm↗
DOE OSTI2017

New Alcohol and Onyx Mixture for Embolization: Feasibility and Proof of Concept in Both In Vitro and In Vivo Models

IntroductionOnyx and ethanol are well-known embolic and sclerotic agents that are frequently used in embolization. These agents present advantages and disadvantages regarding visibility, injection control and penetration depth. Mixing both products might yield a new product with different characteristics. The aim of this study is to evaluate the injectability, radiopacity, and mechanical and occlusive properties of different mixtures of Onyx 18 and ethanol in vitro and in vivo (in a swine model).Materials and MethodsVarious Onyx 18 and ethanol formulations were prepared and tested in vitro for their injectability, solidification rate and shrinkage, cohesion and occlusive properties. In vivo tests were performed using 3 swine. Ease of injection, radiopacity, cohesiveness and penetration were analyzed using fluoroscopy and high-resolution CT.ResultsAll mixtures were easy to inject through a microcatheter with no resistance or blockage in vitro and in vivo. The 50%-ethanol mixture showed delayed copolymerization with fragmentation and proximal occlusion. The 75%-ethanol mixture showed poor radiopacity in vivo and was not tested in vitro. The 25%-ethanol mixture showed good occlusive properties and accepted penetration and radiopacity.ConclusionMixing Onyx and ethanol is feasible. The mixture of 25% of ethanol and 75% of Onyx 18 could be a new sclero-embolic agent. Further research is needed to study the chemical changes of the mixture, to confirm the significance of the added sclerotic effect and to find out the ideal mixture percentages.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Leaching of Degraded Preservative Matrices, Based on Sodium Aluminophosphate Glasses, for High-Level Wastes

The chemical stability of vitrified high-level nuclear industry wastes in contact with water was studied experimentally in application to underground disposal of the wastes. The experiments were performed on samples of sodium aluminophosphate glass used in industrial solidification of wastes. Stable isotopes of strontium, cesium, uranium, and rare-earth elements as geochemical analogs of actinides were introduced into the glass to simulate radionuclides. It was observed that water vapor affects the degradation of the glass when vitrified wastes are placed in temporary repositories. It is shown that as a result of the degradation the rate of leaching of the glass in water increases significantly. In addition, a substantial portion of radionuclide simulators in colloidal form goes into the water medium.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Environmental Effects of Cavitation Technology for Radioactive Waste Management

Results from studies of the removal from storage and solidification of low- and intermediate-level liquid radioactive waste in inorganic binders (cementation) are presented. Cavitation technology for recycling radiochemical wastes from nuclear power plant decommissioning increases the extraction throughput and strength of the cement compound.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Observation of Nanometric Silicon Oxide Bifilms in a Water-Atomized Hypereutectic Cast Iron Powder

This study investigated the reasons for the irregular structure of primary graphite nodules that were formed in a hypereutectic cast iron powder during water atomization. The graphite nodules contain a significant amount of micron-sized pores and multiple nanometric voids that formed from silicon oxide bifilms. The bifilms theory is often used to explain the mechanisms responsible for the presence of pores in castings. However, even if many results presented in the literature tend to corroborate the existence of bifilms, to this date, only indirect evidences of their existence were presented. The observations presented in this paper are the first to show the double-sided nature of these defects. These observations support the bifilms theory and give an explanation for the presence of porosities in castings. The bifilms were used as substrate for graphite growth during solidification. The irregular structure of the graphite nodules is a consequence of the rather random structure of the bifilms that were introduced in the melt as a result of turbulences on the surface of the melt during pouring. The confirmation of the existence of bifilms can contribute to the understanding of the mechanical properties of various metallic parts.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Formation Mechanism of Surface Crack in Low Pressure Casting of A360 Alloy

A surface crack defect is normally found in low pressure castings of Al alloy with a sudden contraction structure. To further understand the formation mechanism of the defect, the mold filling process is simulated by a two-phase flow model. The experimental results indicate that the main reason for the defect deformation is the mismatching between the height of liquid surface in the mold and pressure in the crucible. In the case of filling, a sudden contraction structure with an area ratio smaller than 0.5 is obtained, and the velocity of the liquid front increases dramatically with the influence of inertia. Meanwhile, the pressurizing speed in the crucible remains unchanged, resulting in the pressure not being able to support the height of the liquid level. Then the liquid metal flows back to the crucible and forms a relatively thin layer solidification shell on the mold wall. With the increasing pressure in the crucible, the liquid level rises again, engulfing the shell and leading to a surface crack. As the filling velocity is characterized by the damping oscillations, surface cracks will form at different heights. The results shed light on designing a suitable pressurizing speed for the low pressure casting process.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Numerical Research on Magnetic Field, Temperature Field and Flow Field During Melting and Directionally Solidifying TiAl Alloys by Electromagnetic Cold Crucible

The electromagnetic cold crucible (EMCC) technique is an effective method to melt and directionally solidify reactive and high-temperature materials without contamination. The temperature field and fluid flow induced by the electromagnetic field are very important for melting and controlling the microstructure. In this article, a 3D EMCC model for calculating the magnetic field in the charges (TiAl alloys) using the T-Ω finite element method was established and verified. Magnetic fields in the charge under different electrical parameters, positions and dimensions of the charge were calculated and analyzed. The calculated results show that the magnetic field concentrates in the skin layer, and the magnetic flux density (B) increases with increasing of the frequency, charge diameter and current. The maximum B in the charge is affected by the position of the charge in EMCC (h{sub 1}) and the charge height (h{sub 2}), which emerges at the middle of coils (h{sub c}) when the relationship of h{sub c} < h{sub 1} + h{sub 2} < h{sub c} + δ is satisfied. Lower frequency and smaller charge diameter can improve the uniformity of the magnetic field in the charge. Consequently, the induced uniform electromagnetic stirring weakens the turbulence and improves temperature uniformity in the vicinity of the solid/liquid (S/L) interface, which is beneficial to forming a planar S/L interface during directional solidification. Based on the above conclusions, the TiAlNb alloy was successfully melted with lower power consumption and directionally solidified by the square EMCC.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Crystal Phases Formed in a CaO-Fe 2 O 3 System Under a High Cooling Rate in Air

A CaO-Fe 2 O 3 system is a fundamental binary system for the iron ore sintering process. Although the basic reactions have been investigated since the 1960s, melting and solidification caused by the combustion of coke results in an unstable state owing to extreme temperature variations. In this study, using a hot thermocouple method, samples of 10 pct CaO-90 pct Fe 2 O 3 and 20 pct CaO-80 pct Fe 2 O 3 were melted on a thermocouple and quenched with several techniques. The obtained samples were precisely examined by XRD. It was found that the sample containing 10 pct CaO-90 pct Fe 2 O 3 changed to 10 pct CaO-13 pct FeO-77 pct Fe 2 O 3 under an oxygen partial pressure (P O 2 ) of 0.21 during melting. For the 10 pct CaO sample, the crystal phases found at a low cooling rate (509 K/s) were WF ss , C 4 WF 8 (C: CaO, W: FeO, F: Fe 2 O 3 ), and C 2 W 4 F 9 . When the sample composition was 20 pct CaO, the precipitated crystal phases were C 4 WF 4 , C 4 F 7 , and C 4 WF 8 . On the other hand, the crystal phases for high cooling rates (1590 and 7900 K/s) with 10 pct CaO were WF ss (solid solution of WF and F), F, and C 2 W 4 F 9 . The formation of the equilibrium phases WF ss , F, C 4 WF 4 , and C 4 WF 8 can be understood by examining the isothermal section of the phase diagrams, while the unstable phases C 2 W 4 F 9 and C 4 F 7 are discussed on the basis of the reactions under an equilibrium state.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of Joining Atmosphere in Transient Liquid Phase Bonding of Inconel 617 Superalloy

In the present paper, transient liquid phase (TLP) bonding of Inconel 617 alloy under the different furnace atmospheres of vacuum, argon gas, and air was investigated. The experiments were carried out at 1408 K (1135 °C) for 300 minutes by using BNi-1 filler metals with different thicknesses of 50 and 100 µm. The microstructure, chemical analysis, shear strength, and microhardness of the resultant joints were studied. After 300 minutes, complete isothermal solidification was obtained for both the interlayers having 50 and 100 µm thicknesses under all the furnace atmospheres. The specimens bonded under vacuum condition showed the highest shear strength, failure energy, and ductility. Also, the joint produced under argon gas atmosphere using 100-µm-thick filler metal showed a good strength and may be acceptable in many applications. However, the specimens bonded under air atmosphere were weak, due to their further cavities and non-dissolved carbides. The presence of non-dissolved carbides in the diffusion-affected zone resulted in increasing the hardness of the base metal near the interface. The carbides were dissolved and the hardness of the diffusion-affected zone was reduced under vacuum condition compared to argon and air atmospheres. The best result was obtained for the specimen joined using the 50-µm-thick interlayer under vacuum atmosphere, with about 95.8 pct joint efficiency.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Numerical Modeling of Fiber-Reinforced Metal Matrix Composite Processing by the Liquid Route: Literature Contribution

One of the technologies used to produce metal matrix composites (MMCs) is liquid route processing. One solution is to inject a liquid metal under pressure or at constant rate through a fibrous preform. This foundry technique overcomes the problem of the wettability of ceramic fibers by liquid metal. The liquid route can also be used to produce semiproducts by coating a filament with a molten metal. These processes involve physical phenomena combined with mass and heat transfer and phase change. The phase change phenomena related to solidification and also to the melting of the metal during the process notably result in modifications to the permeability of porous media, in gaps in impregnation, in the appearance of defects (porosities), and in segregation in the final product. In this article, we provide a state-of-the-art review of numerical models and simulation developed to study these physical phenomena involved in MMC processing by the liquid route.

36 MATERIALS SCIENCE↗
DOE OSTI2018

On the Modeling of Thermal Radiation at the Top Surface of a Vacuum Arc Remelting Ingot

Two models have been implemented for calculating the thermal radiation emitted at the ingot top in the VAR process, namely, a crude model that considers only radiative heat transfer between the free surface and electrode tip and a more detailed model that describes all radiative exchanges between the ingot, electrode, and crucible wall using a radiosity method. From the results of the second model, it is found that the radiative heat flux at the ingot top may depend heavily on the arc gap length and the electrode radius, but remains almost unaffected by variations of the electrode height. Both radiation models have been integrated into a CFD numerical code that simulates the growth and solidification of a VAR ingot. The simulation of a Ti-6-4 alloy melt shows that use of the detailed radiation model leads to some significant modification of the simulation results compared with the simple model. This is especially true during the hot-topping phase, where the top radiation plays an increasingly important role compared with the arc energy input. Thus, while the crude model has the advantage of its simplicity, use of the detailed model should be preferred.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Analysis of Brazing Effect on Hot Corrosion Behavior of a Nickel-Based Aerospace Superalloy

The effects of brazing and use of composite powder mixture as interlayer material on hot corrosion resistance of brazed IN738 superalloy were studied. Brazing was observed to result in significant reduction in the hot corrosion resistance of the superalloy. However, application of composite powder mixture, which consists of additive superalloy powder, enhanced the hot corrosion resistance of brazed samples. It is also found that although the use of composite powder mixture increased hot corrosion resistance of brazed alloy, if the additive powder completely melts, which is possible during brazing, it can significantly reduce the hot corrosion resistance of the brazed joint. Elemental micro-segregation during solidification of the joint with completely melted powder mixture produces chromium-depleted zones and consequently reduces hot corrosion resistance, since a uniform distribution and adequate chromium concentration are necessary to combat hot corrosion. This has not been previously reported in the literature and it is crucial to the use of composite powder mixture for enhancing the properties of brazed superalloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Premelting, Melting, and Degradation Properties of Molten Alkali Nitrates: LiNO{sub 3}, NaNO{sub 3}, KNO{sub 3}, and Binary NaNO{sub 3}-KNO{sub 3}

A simultaneous thermal analyzer (STA) was used to observe the transition and degradation events of LiNO{sub 3}, NaNO{sub 3}, KNO{sub 3}, and binary NaNO{sub 3}-KNO{sub 3} salts for potential use as phase change materials (PCMs) and heat transfer fluid (HTF). Samples were heated from 50 °C to 800 °C at 10 °C/min scanning rate in three atmospheres (argon, air, and oxygen) using an STA to observe decomposition behavior. Thermal stability increased for all salts at high partial pressure of O{sub 2} (P{sub O{sub 2}}= 1.0) compared to inert argon (P{sub O{sub 2}}= 0). O{sub 2}, N{sub 2}, NO, N{sub 2}O, and NO{sub 2} were main evolved gases during nitrate decomposition. NO and O{sub 2} started to evolve at approximately the same temperature after melting, indicating that primary and secondary decomposition reactions were concurrent and overlapping. The solid-solid transition, liquidus and solidus temperatures, heat of transition, heat of melting, and heat of solidification were obtained at various heating-cooling rates (1, 2, 4, 5, 6, 8, 10, and 15 °C/min) using an STA. At all heating-cooling rates, a small gap exists between liquidus and solidus temperatures for all samples due to the salts exhibiting supercooling phenomena. This study showed that the degradation point depends on the blanket atmosphere top of the molten salts and that heating rates have a minor effect on transition events (peaks height, peaks width, and transition enthalpies).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Multiphase Model of Semisolid Slurry Generation and Isothermal Holding During Cooling Slope Rheoprocessing of A356 Al Alloy

In the present paper, we present an experimentally validated 3D multiphase and multiscale solidification model to understand the transport processes involved during slurry generation with a cooling slope. In this process, superheated liquid alloy is poured at the top of the cooling slope and allowed to flow along the slope under the influence of gravity. As the melt flows down the slope, it progressively loses its superheat, starts solidifying at the melt/slope interface with formation of solid crystals, and eventually exits the slope as semisolid slurry. In the present simulation, the three phases considered are the parent melt as the primary phase, and the solid grains and air as secondary phases. The air phase forms a definable air/liquid melt interface as the free surface. After exiting the slope, the slurry fills an isothermal holding bath maintained at the slope exit temperature, which promotes further globularization of microstructure. The outcomes of the present model include prediction of volume fractions of the three different phases considered, grain evolution, grain growth, size, sphericity and distribution of solid grains, temperature field, velocity field, macrosegregation and microsegregation. In addition, the model is found to be capable of making predictions of morphological evolution of primary grains at the onset of isothermal coarsening. The results obtained from the present simulations are validated by performing quantitative image analysis of micrographs of the rapidly oil-quenched semisolid slurry samples, collected from strategic locations along the slope and from the isothermal slurry holding bath.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evolution of Non-metallic Inclusions and Precipitates in Oriented Silicon Steel

The evolution of inclusions in oriented silicon steel during the manufacturing process was carried out by chemical composition analysis, non-aqueous electrolytic corrosion, and thermodynamic calculation. The morphology, composition, and size of inclusions were analyzed introducing field emission scanning electron microscope. The oxides were mainly formed during the secondary refining, and the nitrides, sulfides, and compounds were formed during the solidification and cooling of steel in the processes of continuous casting and hot rolling.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and Properties of the Al-27Si/Cu/Al-50Si Joint Brazed by the Partial Transient Liquid Phase Bonding

Al-27Si and Al-50Si were brazed by using a thin Cu interlayer. The metallurgical bonding without obvious defects is achieved, and a wide brazing seam consisting of fine eutectic structures and coarse Si particles is formed in the Al-27Si/Cu/Al-50Si joint. The deposition of Si element in the liquid phases during solidification results in the formation of the larger Si particles and ultra-small Si particles in the brazing seam. The shear strength of the joint reaches 63 MPa.

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↗