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The processing of yttria, zirconia, and alumina under weightless conditions is discussed. The process consists of levitation or position control, heating and melting, superheating, and supercooling. The use of arc imaging furnaces, lasers, induction heating, microwave, and electron beam methods are analyzed to show the advantages and disadvantages of each.
An acoustic positioning system is described that is adaptable to a range of processing chambers and furnace systems. Operation at temperatures exceeding 1000 C is demonstrated in experiments involving the levitation of liquid and solid glass materials up to several ounces in weight. The system consists of a single source of sound that is beamed at a reflecting surface placed a distance away. Stable levitation is achieved at a succession of discrete energy minima contained throughout the volume between the reflector and the sound source. Several specimens can be handled at one time. Metal discs up to 3 inches in diameter can be levitated, solid spheres of dense material up to 0.75 inches diameter, and liquids can be freely suspended in l-g in the form of near-spherical droplets up to 0.25 inch diameter, or flattened liquid discs up to 0.6 inches diameter. Larger specimens may be handled by increasing the size of the sound source or by reducing the sound frequency.
Experimental demonstration of the effects of diffusion on aluminum depletion and degradation in NiAl coatings on superalloys. Pack aluminized IN 100 and Mar-M200 were vacuum annealed at 1100 C to allow diffusion to proceed independently of oxidation. As-coated and as-diffused coatings were compared before and after cyclic furnace oxidation at 1100 C. The extent of degradation was judged by specific weight change, metallography, and electron microprobe analyses.
Vacuum extraction with subsequent mass spectrometric analysis of evolved volatiles was selected as the analytical procedure. The high-vacuum gas-handling system was constructed of stainless steel. The system was completely free from mercury, grease, or volatile organic materials. The furnace for heating the samples is discussed together with the high-vacuum crusher, the mass spectrometer, and approaches for water determination. The analytical procedure is considered, giving attention to the extraction of volatiles, adsorption studies, and the analysis of volatiles.
A joining process, designated weld-brazing, which combines resistance spot-welding and brazing has been developed at the NASA Langley Research Center. Resistance spot-welding is employed to position and aline the parts and to establish a suitable faying surface gap for brazing and contributes to the integrity of the joint. Brazing enhances the properties of the joint and reduces the stress concentrations normally associated with spotwelds. Ti-6Al-4V titanium alloy joints have been fabricated using 3003 aluminum braze both in a vaccum furnace and in a retort containing an inert gas environment.
Initial experiments conducted during the Apollo 14 mission demonstrated that unique dispersions of immiscible materials could be obtained by processing in a low gravity environment. Subsequently, seven metallic systems have been processed in three NASA facilities: the drop tower at MSFC, the M-512 facility on board a KC-135 aircraft and the M-518 furnace on board Skylab. All couples were solidified from the liquid while in a low gravity environment, with one gravity processed specimens as controls. Metallographic examination demonstrated that the specimens processed in a low gravity environment exhibited a more uniform dispersion and microstructure than the one gravity processed controls.
A joining process, designated weld-brazing, which combines resistance spotwelding and brazing has been developed at the NASA Langley Research Center. Resistance spot-welding is employed to position and align the parts and to establish a suitable faying surface gap for brazing; it contributes to the integrity of the joint. Brazing enhances the properties of the joint and reduces the stress concentrations normally associated with spotwelds. Ti-6Al-4V titanium alloy joints have been fabricated using 3003 aluminum braze both in a vacuum furnace and in a retort containing an inert gas environment.
Experiments were performed to critically demonstrate the effects of diffusion on the aluminum depletion and degradation of NiAl coatings on superalloys. Pack aluminized IN 100 and Mar-M200 were diffusion annealed in 5 mtorr vacuum at 1100 C for 300 hr. Aluminum losses due to oxidation and vaporization were minimal. Metallographic and electron microprobe analyses showed considerable interdiffusion of the coating with the substrate, which caused a large decrease in the original aluminum level of the coating. Subsequent cyclic furnace oxidation tests were performed at 1100 C using 1 hr cycles on prediffused and as-coated specimens. The prediffusion treatment decreased the oxidation and as-coated specimens. The prediffusion treatment decreased the oxidation protection for both alloys, but more dramatically for IN 100. Identical oxidation tests of bulk NiAl, where such diffusion effects are precluded, showed no signs of degradation at twice the time needed to degrade the coated superalloys.
The M553 Sphere Forming Experiment conducted in the M512 Furnace Facility during Skylab II was designed to study the effects of weightlessness on the solidification process. Results indicated that there was an outstanding record of solidification terracing and solute redistribution, and that this record may be better than obtainable terrestrially. The solute redistribution was found to be highly localized to prescribed crystallographic systems. It was also shown that for some experimental conditions in a space environment, the anticipated solid/liquid solidification process was perturbed and a solid/liquid/gas reaction took place during solidification. It is felt that these results will contribute to the understanding of terrestrial solidification and will contribute to future space processing considerations.
Transport mechanisms of zinc atoms in molten zinc were investigated by radiotracer techniques in unit and in near-zero gravity environments. Each melt in the Skylab flight experiments was maintained in a thermal gradient of 420 C to 790 C. Similar tests were performed in a unit gravity environment for comparison. After melting in the gradient furnace followed by a thermal soak period (the latter was used for flight samples only), the samples were cooled and analyzed for Zn-65 distribution. All samples melted in a unit gravity environment were found to have uniform Zn-65 distribution - no concentration gradient was observed even when the sample was brought rapidly to melting and then quenched. Space-melted samples, however, showed textbook distributions, obviously the result of diffusion. It was evident that convection phenomena were the dominant factors influencing zinc transport in unit gravity experiments, while diffusion was the dominant factor in near-zero gravity experiments.
Eleven coating systems based on MCrAlY overlay and diffusion aluminide prototypes were evaluated to determine their capability for protecting the gamma/gamma prime-delta directionally solidified eutectic alloy (Ni-20Cb-6Cr-2.5Al) in gas turbine engine applications. Furnace oxidation and hot corrosion, Mach 0.37 burner-rig, tensile ductility, stress-rupture and thermomechanical fatigue tests were used to evaluate the coated gamma/gamma prime-delta alloy. The diffusion aluminide coatings provided adequate oxidation resistance at 1144 K (1600 F) but offered very limited protection in 114 K (1600 F) hot corrosion and 1366 K (2000 F) oxidation tests. A platinum modified NiCrAlY overlay coating exhibited excellent performance in oxidation testing and had no adverse effects upon the eutectic alloy.
The microstructure of the alpha titanium alloy Ti-5Al-2.5Sn and the metastable beta titanium alloy Beta 3 was examined. The material was from normal and extra low interstitial grade plates which were either air-cooled or furnace-cooled from an annealing treatment. Beta 3 was studied in alpha-aged and omega-aged plates which were heat treated to similar strength levels. Tensile and plane strain fracture toughness tests were conducted at room temperature on the alpha-aged material. The microstructure and fracture mechanisms of alloys were studied using optical metallography, electron microscopy, microprobe analyses, and texture pole figures. Future experiments are described.
An evaluation of two different pyrolysis concepts which recover energy from solid waste was conducted in order to determine the merits of each concept for integration into a Integrated Utility System (IUS). The two concepts evaluated were a Lead Bath Furnace Pyrolysis System and a Slagging Vertical Shaft, Partial Air Oxidation Pyrolysis System. Both concepts will produce a fuel gas from the IUS waste and sewage sludge which can be used to offset primary fuel consumption in addition to the sanitary disposal of the waste. The study evaluated the thermal integration of each concept as well as the economic impact on the IUS resulting from integrating each pyrolysis concepts. For reference, the pyrolysis concepts were also compared to incineration which was considered the baseline IUS solid waste disposal system.
The Skylab Materials Processing Facility is described. Eight experiments on metal processing under near-zero-gravity conditions were performed in this facility. Three of these involved metals and procedures of potential application to fabrication in space. A Multipurpose electric furnace within the Materials Processing Facility was employed to heat three ampoules of samples for each of the other five experiments. These five investigations cover diffusion versus convection rates in molten zinc, several immiscible alloy compositions, a whisker-reinforced silver-based composite, heat treating of porous silver samples, and a copper-aluminum eutectic.
The space processing experiments performed during the Skylab missions included one on single crystal growth of germanium selenide and telluride, one on pure and doped germanium crystals, two on pure and doped indium antimonide, one on gallium-indium-antimony systems, and one on a sodium chloride-sodium fluoride eutectic. In each experiment, three ampoules of sample were processed in the multipurpose electric furnace within the Skylab Materials Processing Facility. All were successful in varying degrees and gave important information about crystal growth removed from the effects of earth surface gravity.
The extent was investigated to which experiment hardware and operational requirements can be met by automatic control and material handling devices; payload and system concepts that make extensive use of automation technology are defined. Hardware requirements for each experiment were established and tabulated, and investigations of applicable existing hardware were documented. The capabilities and characteristics of industrial automation equipment, controls, and techniques are presented in the form of a summary of applicable equipment characteristics in three basic mutually-supporting formats. Facilities for performing groups of experiments are defined along with four levitation groups and three furnace groups; major hardware elements required to implement them were identified. A conceptual design definition of ten different automated processing facilities is presented along with the specific equipment to implement each facility and the design layouts of the different units. Constraints and packaging, weight, and power requirements for six payloads postulated for shuttle missions in the 1979 to 1982 time period were examined.
The net radiation method is developed for systems having both opaque and partially transparent walls. Heat convection is present at the surfaces and heat conduction through the windows is taken into account. Specific equations are derived for a window between two parallel plates, where one plate is at an elevated temperature typical of what would be encountered in an electric furnace, and the other plate is being cooled. A two-band model is used with cutoff wavelengths typical of glass or quartz. Numerical results are obtained for the window temperature and the heat flow through the window. The effect on these quantities of various plate temperatures and emissivities is shown.
Three lines of the fundamental rotation-vibration band of CN have been observed in the laboratory using a King furnace. The transition moment squared has been found to be .00075 plus or minus .00031 atomic units. In addition, the transition moment squared of the 0-0 band of the red system of CN has been measured to be 0.48 plus or minus 0.28 atomic units (an oscillator-strength of .00033 plus or minus .0019).