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Study examines and reports positive findings from suitability tests of metal alloys, Inconel 718 and Ti-6A1-4V and elastomers, Ethylene propylene terpolymer rubbers, for utilization in storage vessels, fluid lines, and other system components subjected to continuous immersion in liquid anhydrous ammonia.
Unnotched and notched tensile properties of stressed and unstressed specimens of wrought 316 stainless steel, Incology 903, Monel K-500, and cast specimens of Inconel 718 were examined. Environmental tests were performed in atmospheric pressure air, high pressure nitrogen, and high pressure oxygen. Results show that oxygen did not alter the tensile properties of any of the alloys studied.
Volatilization of oxides during cyclic oxidation of commercial Nichrome, Inconel 750, Rene 41, Stellite 6B, and GE-1541 was studied at 1200 C in static air. Quantitative analysis of oxide vapor deposits revealed that oxides of tungsten, molybdenum, niobium, manganese, and chromium volatilized preferentially from the oxide scales. Aluminum and silicon were not detected in vapor deposits. For all the alloys except GE-1541, chromium was found to be the main metallic element in the oxide scales.
It is recognized that the use of overwrapped pressure vessels with load sharing liners may provide significant weight savings for high pressure gas containment in Space Shuttle Orbiter systems. The technology readiness to produce Kevlar wound vessels with load sharing liners of titanium 6Al-4V, Inconel 718 or cryoformed 301 steel has been demonstrated. It has been estimated that about 400 lbs can be saved in the Orbiter by using overwrapped vessels with load sharing liners instead of monolithic metal designs. Total weight of the composite vessels would be about 1350 lbs as opposed to about 1750 lbs for all-metal vessels.
A jet-stirred combustor, constructed of castable zirconia and with an Inconel injector, was used to study nitric oxide formation in propane-air combustion with residence times in the range from 3.2 to 3.3 msec and equivalence ratios varying from 0.7 to 1.4. Measurements were made of combustor operating temperature and of nitric oxide concentration. Maximum nitric oxide concentrations of the order of 55 ppm were found in the range of equivalence ratio from 1.0 to 1.1. A finite-rate chemical kinetic mechanism for propane combustion and nitric oxide formation was assembled by coupling an existing propane oxidation mechanism with the Zeldovich reactions and reactions of molecular nitrogen with hydrocarbon fragments. Analytical studies using this mechanism in a computer simulation of the experimental conditions revealed that the hydrocarbon-fragment-nitrogen reactions play a significant role in nitric oxide formation during fuel-rich combustion.
The Materials and Processes Laboratory evaluation of Solid Rocket Boosters (SRB) and Solid Rocket Motors (SRM) candidate material, both in-house and with ocean exposure tests at Panama City and Kennedy Space Center (KSC), Florida is presented. Early sample tests showed excellent seawater corrosion resistance for inconel 718 and titanium 6A1-4V alloys. Considerable corrosion and biofouling occurred with bare 2219-T87 aluminum. Subsequent tests conclusively demonstrated that epoxy coatings prevented corrosion of 2219-T87 aluminum as long as the coatings stays intact. The results and assessment of the series of ocean environmental tests that were conducted are also presented.
Volatilization of oxides during cyclic oxidation of commercial Nichrome, Inconel 750, Rene 41, Stellite 6B, and GE-1541 was studied at 1200 C in static air. Quantitative analysis of oxide vapor deposits revealed that oxides of tungsten, molybdenum, niobium, manganese, and chromium volatilized preferentially from the oxide scales. Aluminum and silicon were not detected in vapor deposits. For all the alloys except GE-1541 chromium was found to be the main metallic element in the oxide scales.
The use of atmospheric drag to circularize an elliptical spacecraft orbit at Venus is analyzed parametrically for the Venus Orbital Imaging Radar Mission (VOIR) in 1983. Navigation, maneuver, and guidance requirements are discussed for the decay of a 24-hr orbit to a close circular orbit in about 30-60 days. A prototype 'Aerobrake' is described which is approximately 5 m in diameter and 25 kg in mass and which replaces a chemical retroengine of about 1300 kg in mass (delta V = 2.5 km/s) by a 700 kg in-orbit mass. The aerobrake, a light deployable Inconel sheet, shields the spacecraft from the flow and radiates the aerodynamic heating.
During the development of the Space Shuttle Orbiter propulsion and environmental control subsystems it was recognized that use of composite pressure vessels with load sharing liners could provide significant weight savings for high pressure gas containment. A program is described which was undertaken to assess the utility for orbiter applications of titanium 6Al-4V and Inconel 718 liners overwrapped with Kevlar fibers. Vessel characteristics, design features and test results are presented along with brief descriptions of processes and nondestructive evaluation techniques. The resolutions of anomalies and development of design are also presented. Fracture control as applied to the orbiter composite vessels is briefly discussed. Five of the seven titanium lined vessels in the program experienced premature cyclic failures. These failures were shown to be primarily due to metallurgical anomalies rather than an inherent composite design problem. A nonfragmentary leakage mode of failure was demonstrated at operating pressures. The composite designs will be approximately 25 percent lighter than their all metal counterparts.
Mild steel (AISI 1018) was selected as model cold rolling material and Ti-6A1-4V and Inconel 718 were selected as typical hot rolling and cold rolling alloys, respectively. The flow stress and workability of these alloys were characterized and friction factor at the roll/workpiece interface was determined at their respective working conditions by conducting ring tests. Computer-aided mathematical models for predicting metal flow and stresses, and for simulating the shape rolling process were developed. These models utilized the upper bound and the slab methods of analysis, and were capable of predicting the lateral spread, roll separating force, roll torque, and local stresses, strains and strain rates. This computer-aided design system was also capable of simulating the actual rolling process, and thereby designing the roll pass schedule in rolling of an airfoil or a similar shape.
Work performed on this contract was primarily for the evaluation of selected electrode materials for thermionic energy converters. The original objective was to characterize selected nickel based superalloys up to temperatures of 1400 K. It was found that an early selection, Inconel 800 produced a high vapor pressure which interfered with the vacuum emission measurements. The program then shifted to two other areas. The first area was to obtain emission from the superalloys in a cesiated atmosphere. The cesium plasma helps to suppress the vaporization interference. The second area involved characterization of the Lanthanum-Boron series as thermionic emitters. These final two areas resulted in three journal publications which are attached to this report.
A typical 625 Inconel pressure vessel, equipped with four thermocouples, has voltage taps not only for the cell, but for each of the several packs inside the container. In a two-stack design, a weld ring is used to separate the packs which, joined together, form one solid group. In the four-stack design, stacks are separated mechanically with about half inch Plexiglas and are connected through the center. Electrolytes are forced out by vacuum. The two stack design is intended for 500 psi and was pressure tested up to 1,000. The problem of electrolyte shorts is discussed and possible solutions for its correction are given.
Mild steel (AISI 1018) was selected as model cold-rolling material and Ti-6Al-4V and INCONEL 718 were selected as typical hot-rolling and cold-rolling alloys, respectively. The flow stress and workability of these alloys were characterized and friction factor at the roll/workpiece interface was determined at their respective working conditions by conducting ring tests. Computer-aided mathematical models for predicting metal flow and stresses, and for simulating the shape-rolling process were developed. These models utilize the upper-bound and the slab methods of analysis, and are capable of predicting the lateral spread, roll-separating force, roll torque and local stresses, strains and strain rates. This computer-aided design (CAD) system is also capable of simulating the actual rolling process and thereby designing roll-pass schedule in rolling of an airfoil or similar shape. The predictions from the CAD system were verified with respect to cold rolling of mild steel plates. The system is being applied to cold and hot isothermal rolling of an airfoil shape, and will be verified with respect to laboratory experiments under controlled conditions.
Two studies are described in which CAD methods are used for preliminary design of advanced earth-to-orbit transport wings. The first structural concept was a multilayer honeycomb wing composed of diffusion-bonded Inconel 718; the second concept (in which structural simplicity was sought) involved a honeycomb sandwich wing, for which only a leading edge and trailing edge spar were used. Some new technologies applicable to advanced wing designs are briefly discussed.
Parameters that produce high-integrity overlay welds in Incoloy-903, Incoloy-88, and Inconel-718 differ from those in conventional metal-in groove welds. Reduced weld velocity eliminates underbead crack-inducing level.
Rugged, compact heater is made from 0.1 mm diameter Inconel wire (125 ohms per meter). Heating element is enclosed in PTFE heat-shrink sleeve. Ends of coal pass through small ceramic spools and are silver-brazed to lead wires. Junctions are potted in epoxy or silicon and covered with crimp sleeves and heat-shrink tubing.
This paper is a description of recent work to establish the feasibility of aerobraking for planetary orbit missions. Primary emphasis is on a close (300 km) Venus orbiter in 1984. Performance advantages for close Mars orbiters and geosynchronous round trip missions are also shown. A description of the aerobraking operations scenario is given and encouraging preliminary results of an orbit determination analysis are cited. A spacecraft design is presented that features a forward aeroshield and a 9-meter aft aerobrake of 2 mil Inconel. It is shown that, with relatively minor modifications the current Venus Orbital Imaging Radar (VOIR) mission spacecraft design can be adapted to aerobraking and that the aerobraking concept enables the VOIR mission in the difficult 1986 and 1988 opportunities.
The radio frequency sputtering technique was used to deposite a hard refractory, chromium oxide coating on an Inconel X-750 foil 0.1 mm thick. Optimized sputtering parameters for a smooth and adherent coating were found to be as follows: target-to-substrate spacing, 41.3 mm; argon pressure, 5-10 mTorr; total power to the sputtering module, 400 W (voltage at the target, 1600 V), and a water-cooled substrate. The coating on the annealed foil was more adherent than that on the heat-treated foil. Substrate biasing during the sputter deposition of Cr2O3 adversely affected adherence by removing naturally occurring interfacial oxide layers. The deposited coatings were amorphous and oxygen deficient. Since amorphous materials are extremely hard, the structure was considered to be desirable.