Electrostatic Sample Levitator for Containerless Materials Processing
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Measurements of Thermophysical Properties of Molten Silicon and Geranium
The objective of this ground base program is to measure thermophysical properties of molten/ undercooled silicon, germanium, and Si-Ge alloys using a high temperature electrostatic levitator and in clearly assessing the need of the microgravity environment to achieve the objective with higher degrees of accuracy. Silicon and germanium are two of the most important semiconductors for industrial applications: silicon is unsurpassed as a microelectronics material, occupying more than 95% of the electronics market. Si-Ge alloy is attracting keen interest for advanced electronic and optoelectronic applications in view of its variable band gap and lattice parameter depending upon its composition. Accurate thermophysical properties of these materials are very much needed in the semiconductor industry for the growth of large high quality crystals.
Rhim, Won-Kyu↗
Environment Conscious Ceramics (Ecoceramics): An Eco-Friendly Route to Advanced Ceramic Materials
Environment conscious ceramics (Ecoceramics) are a new class of materials, which can be produced with renewable natural resources (wood) or wood wastes (wood sawdust). This technology provides an eco-friendly route to advanced ceramic materials. Ecoceramics have tailorable properties and behave like ceramic materials manufactured by conventional approaches. Silicon carbide-based ecoceramics have been fabricated by reactive infiltration of carbonaceous preforms by molten silicon or silicon-refractory metal alloys. The fabrication approach, microstructure, and mechanical properties of SiC-based ecoceramics are presented.
Singh, M.↗
Metallurgical Mechanisms Controlling Mechanical Properties of Aluminum Alloy 2219 Produced by Electron Beam Freeform Fabrication
The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties demonstrated for electron beam deposited aluminum and titanium alloys are comparable to wrought products, although the microstructures of the deposits exhibit cast features. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. Tensile mechanical properties and microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains with interior dendritic structures, described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processing-microstructure-property correlations.
Domack, Marcia S.↗
Metallurgical Mechanisms Controlling Mechanical Properties of Aluminum Alloy 2219 Produced By Electron Beam Freeform Fabrication
The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties have been demonstrated for electron beam deposited aluminum and titanium alloys that are comparable to wrought products, although the microstructures of the deposits exhibit features more typical of cast material. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. In the current study, mechanical properties and resulting microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Material performance was evaluated based on tensile properties and results were compared with properties of Al 2219 wrought products. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains, typically with interior dendritic structures, which were described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processing-microstructure-property correlations.
Domack, Marcia S.↗
Properties of pure nickel after long term exposures to LiOH and vacuum at 775 K
The solid to liquid phase transformation of LiOH at 744.3 K is considered to be an ideal candidate thermal energy storage (TES) mechanism for a Rankine heat engine based solar dynamic system operating at approximately 682 K. While pure nickel is thought to be a suitable containment material for LiOH, long term containment is of concern because molten hydroxides are usually corrosive. Two commercially pure nickel alloys, Ni-200 and Ni-201, were exposed to molten LiOH, its vapor, and vacuum at 775 K for periods ranging from 50 to 5000 h, and simple mechanical property measurements (77 to 900 K tensile and 750 K creep rupture) of exposed alloys were undertaken. The mechanical property test procedures are described and tabular lists of the test data are presented.
Whittenberger, J. D.↗
Structural Fluctuations and Thermophysical Properties of Molten II-VI Compounds
Recently, in support of the microgravity experiment entitled "Crystal Growth of Selected 11-VI Semiconducting Alloys by Directional Solidification," the viscosity of HgZnTe pseudobinary melt was measured using an oscillating-cup viscometer at NASA/Marshall Space Flight Center (MSFC). An unexpected time drift of the measured viscosity, which shows a slow relaxation phenomena at temperatures near the liquidus point, was reproducibly observed. Two sets of data were obtained by cooling the Hg(0.84)Zn(0.16)Te melt from 850 C and stabilizing at temperatures of 790 C, which is just above the liquidus temperature, and stabilizing at temperature of 810 C. While it took one day to reach equilibration at 810 C, five days were required at 790 C A similar relaxation phenomenon was also observed in the measured density of the same liquid. Furthermore, in the density measurements of the HgCdTe melts, which is the pseudobinary system studied in another flight experiment entitled "Growth of Solid Solution Single Crystals," a negative thermal expansion was reported. The liquid density increases from the liquidus point to a maximum value at a temperature approximately 700 C above the liquidus, where normal thermal expansion progressively resumes.
Su, Ching-Hua↗
Mechanical properties of Haynes Alloy 188 after exposure to LiF-22CaF2, air, and vacuum at 1093 K for periods up to 10,000 hours
As part of a program to provide reassurance that the cobalt-base superalloy Haynes Alloy 188 can adequately contain a LiF-CaF2 eutectic thermal energy storage salt, 4900- and 10,000-hr exposures of Haynes Alloy 188 to LiF-22CaF2, its vapor, vacuum, and air at 1093 K have been undertaken. Following such exposures, the microstructure has been characterized and the 77 to 1200 K tensile properties measured. In addition, 1050 K vacuum creep-rupture testing of as-received and molten salt- and vacuum-exposed samples has been undertaken. Although slight degradation of the mechanical properties of Haynes Alloy 188 due to prior exposure was observed, basically none of the losses could be ascribed to a particular environment. Hence, observed decreases in properties are due to thermal aging effects, not corrosive attack. In view of these findings, Haynes Alloy 188 is still deemed to be suitable for containment of the eutectic LiF-CaF2 thermal energy storage media.
Whittenberger, J. D.↗
A Quasi-Containerless Pendant Drop Method for Surface Tension Measurements of Molten Metals and Alloys
A quasi-containerless pendant drop method for measuring the surface tension of molten metals and alloys is being developed. The technique involves melting the end of a high-purity metal rod by bombardment with an electron beam to form a pendant drop under ultra-high vacuum conditions to minimize surface contamination.
surface tension thermophysical property↗
Metal melting, joining, and alloying under weightlessness
During the Skylab mission experiments were conducted concerning the influence of weightlessness on molten metals and the solidification process. It was found that the absence of gravity-induced thermal convection and sedimentation modified the properties of the bulk melt. A metals melting experiment was conducted to study the behavior of metal melted by an electron beam and to evaluate the feasibility of joining metals in space. An exothermic brazing experiment investigated the spreading, mixing, and capillary flow of molten braze material. The containerless melting and solidification of small samples of several metals was studied in another experiment. A description is also given of a study of the directional solidification of solid solution alloys.
Snyder, R. S.↗
Powder-Metallurgy Process And Product
Rapid-solidification processing yields alloys with improved properties. Study undertaken to extend favorable property combinations of I/M 2XXX alloys through recently developed technique of rapid-solidification processing using powder metallurgy(P/M). Rapid-solidification processing involves impingement of molten metal stream onto rapidly-spinning chill block or through gas medium using gas atomization technique.
Paris, Henry G.↗
Thermophysical Property Measurements of Silicon-Transition Metal Alloys
Metals and metallic alloys often have high melting temperatures and highly reactive liquids. Processing reactive liquids in containers can result in significant contamination and limited undercooling. This is particularly true for molten silicon and it alloys. Silicon is commonly termed "the universal solvent". The viscosity, surface tension, and density of several silicon‐transition metal alloys were determined using the Electrostatic Levitator system at the Marshall Space Flight Center. The temperature dependence of the viscosity followed an Arrhenius dependence, and the surface tension followed a linear temperature dependence. The density of the melts, including the undercooled region, showed a linear behavior as well. Viscosity and surface tension values were obtain for several of the alloys in the undercooled region.
Banish, R. Michael↗
Cast Aluminum Alloys for High Temperature Applications Using Nanoparticles Al2O3 and Al3-X Compounds (X = Ti, V, Zr)
In this paper, the effect of nanoparticles Al2O3 and Al3-X compounds (X = Ti, V, Zr) on the improvement of mechanical properties of aluminum alloys for elevated temperature applications is presented. These nanoparticles were selected based on their low cost, chemical stability and low diffusions rates in aluminum at high temperatures. The strengthening mechanism at high temperature for aluminum alloy is based on the mechanical blocking of dislocation movements by these nanoparticles. For Al2O3 nanoparticles, the test samples were prepared from special Al2O3 preforms, which were produced using ceramic injection molding process and then pressure infiltrated by molten aluminum. In another method, Al2O3 nanoparticles can also be homogeneously mixed with fine aluminum powder and consolidated into test samples through hot pressing and sintering. With the Al3-X nanoparticles, the test samples are produced as precipitates from in-situ reactions with molten aluminum using conventional permanent mold or die casting techniques. It is found that cast aluminum alloy using nanoparticles Al3-X is the most cost effective method to produce high strength aluminum alloys for high temperature applications in comparison to nanoparticles Al2O3. Furthermore, significant mechanical properties retention in high temperature environment could be achieved with Al3-X nanoparticles, resulting in tensile strength of nearly 3 times higher than most 300- series conventional cast aluminum alloys tested at 600 F.
Lee, Jonathan A.↗
Affordable, Robust Ceramic Joining Technology (ARCJoinT) Given 1999 R and D 100 Award
Advanced ceramics and fiber-reinforced ceramic matrix composites with high strength and toughness, good thermal conductivity, thermal shock resistance, and oxidation resistance are needed for high-temperature structural applications in advanced high-efficiency and high-performance engines, space propulsion components, and land-based systems. The engineering designs of these systems require the manufacturing of large parts with complex shapes, which are either quite expensive or impossible to fabricate. In many instances, it is more economical to build complex shapes by joining together simple geometrical shapes. Thus, joining has been recognized as an enabling technology for the successful utilization of advanced ceramics and fiber-reinforced composite components in high-temperature applications. However, such joints must retain their structural integrity at high temperatures and must have mechanical strength and environmental stability comparable to those of the bulk materials. In addition, the joining technique should be robust, practical, and reliable. ARCJoinT, which is based on the reaction-forming approach, is unique in terms of producing joints with tailorable microstructures. The formation of joints by this approach is attractive since the thermomechanical properties of the joint interlayer can be tailored to be very close to those of the base materials. In addition, high-temperature fixturing is not needed to hold the parts at the infiltration temperature. The joining process begins with the application of a carbonaceous mixture in the joint area, holding the items to be joined in a fixture, and curing at 110 to 120 C for 10 to 20 min. This step fastens the pieces together. Then, silicon or a silicon alloy in tape, paste, or slurry form is applied around the joint region and heated to 1250 to 1425 C (depending on the type of infiltrant) for 10 to 15 min. The molten silicon or silicon-refractory metal alloy reacts with carbon to form silicon carbide with controllable amounts of silicon and other phases as determined by the alloy composition. Joint thickness can be readily controlled through adjustments of the properties of the carbonaceous paste and the applied fixturing force. The photograph shows various shapes of silicon-carbide-based ceramics and fiberreinforced composites that have been joined using ARCJoinT. Thermomechanical and thermochemical characterization of joints is underway for a wide variety of silicon-carbidebased advanced ceramics and fiber-reinforced composites under the hostile environments that will be encountered in engine applications. ARCJoinT, which was developed by researchers at the NASA Glenn Research Center at Lewis Field, received R&D Magazine's prestigious R&D 100 Award in 1999.
Singh, Mrityunjay↗
Environment Conscious Ceramics (Ecoceramics)
Environment conscious ceramics (Ecoceramics) are a new class of materials, which can be produced with renewable natural resources (wood) or wood wastes (wood sawdust). Silicon carbide-based ecoceramics have been fabricated by reactive infiltration of carbonaceous preforms by molten silicon or silicon-refractory metal alloys. These carbonaceous preforms have been fabricated by pyrolysis of solid wood bodies at 1000 C. The fabrication approach, microstructure, and mechanical properties of SiC-based ecoceramics are presented. Ecoceramics have tailorable properties and behave like ceramic materials manufactured by conventional approaches.
Singh, Mrityunjay↗
High-temperature molten salt thermal energy storage systems for solar applications
Experimental results of compatibility screening studies of 100 salt/containment/thermal conductivity enhancement (TCE) combinations for the high temperature solar thermal application range of 704 deg to 871 C (1300 to 1600 F) are presented. Nine candidate containment/HX alloy materials and two TCE materials were tested with six candidate solar thermal alkali and alkaline earth carbonate storage salts (both reagent and technical grade of each). Compatibility tests were conducted with salt encapsulated in approx. 6.0 inch x 1 inch welded containers of test material from 300 to 3000 hours. Compatibility evaluations were end application oriented, considering the potential 30 year lifetime requirement of solar thermal power plant components. Analyses were based on depth and nature of salt side corrosion of materials, containment alloy thermal aging effects, weld integrity in salt environment, air side containment oxidation, and chemical and physical analyses of the salt. A need for more reliable, and in some cases first time determined thermophysical and transport property data was also identified for molten carbonates in the 704 to 871 C temperature range. In particular, accurate melting point (mp) measurements were performed for Li2CO3 and Na2CO3 while melting point, heat of fusion, and specific heat determinations were conducted on 81.3 weight percent Na2CO3-18.7 weight percent K2CO3 and 52.2 weight percent BaCO3-47.8 weight percent Na2CO3 to support future TES system design and ultimate scale up of solar thermal energy storage (TES) subsystems.
Petri, R. J.↗
Undercooling of materials during solidification in space
The theoretical and actual effect of undercooling on molten materials below the equilibrium solid us temperature was studied. Materials in the categories of pure metals, alloys, and compounds were examined: their commercial and scientific value and past experience in their undercooling were considered. The material properties influencing undercooling behavior are reviewed, specified, and categorized. The effects of gravity and its absence are investigated. It is shown that presence of heterogeneous nucleating agents is the main obstacle to achieving a large degree of undercooling.
Moak, D. P.↗
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.
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