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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Pitting of Space Shuttle's Inconel Honeycomb Conical Seal Panel

This paper describes the approach, findings, conclusions and recommendations associated with the investigation of the conical seal pitting. It documents the cause and contributing factors of the pitting, the means used to isolate each contributor, and the supporting evidence for the primary cause of the pitting. Finally, the selection, development and verification of the repair procedure used to restore the conical seal panel is described with supporting process and metallurgical rationale for selection.

Zimmerman, Frank↗
NASA NTRS2006

Pitting and Repair of the Space Shuttle's Inconel(Registered TradeMark) Honeycomb Conical Seal Panel

During return to flight servicing of the rudder speed brake (RSB) for each Space Shuttle Orbiter, inspectors discovered numerous small pits on the surface of the #4 right hand side honeycomb panel that covers the rudder speed brake actuators. Shortly after detection of the problem, concurrent investigations were initiated to determine the extent of damage, the root cause, and to develop a repair plan, since fabrication of a replacement panel is impractical for cost, schedule, and sourcing considerations. This paper describes the approach, findings, conclusions and recommendations associated with the investigation of the conical seal pitting. It documents the cause and contributing factors of the pitting, the means used to isolate each contributor, and the supporting evidence for the primary cause of the pitting. Finally, the selection, development and verification of the repair procedure used to restore the conical seal panel is described with supporting process and metallurgical rationale for selection.

Zimmerman, Frank R.↗
NASA NTRS1986

Corrosion pitting of SiC by molten salts

The corrosion of SiC by thin films of Na2CO3 and Na2SO4 at 1000 C is characterized by a severe pitting attack of the SiC substrate. A range of different Si and SiC substrates were examined to isolate the factors critical to pitting. Two types of pitting attack are identified: attack at structural discontinuities and a crater-like attack. The crater-like pits are correlated with bubble formation during oxidation of the SiC. It appears that bubbles create unprotected regions, which are susceptible to enhanced attack and, hence, pit formation.

Jacobson, N. S.↗
NASA NTRS1996

Impingement-Current-Erosion Characteristics of Accelerator Grids on Two-Grid Ion Thrusters

Accelerator grid sputter erosion resulting from charge-exchange-ion impingement is considered to be a primary cause of failure for electrostatic ion thrusters. An experimental method was developed and implemented to measure erosion characteristics of ion-thruster accel-grids for two-grid systems as a function of beam current, accel-grid potential, and facility background pressure. Intricate accelerator grid erosion patterns, that are typically produced in a short time (a few hours), are shown. Accelerator grid volumetric and depth-erosion rates are calculated from these erosion patterns and reported for each of the parameters investigated. A simple theoretical volumetric erosion model yields results that are compared to experimental findings. Results from the model and experiments agree to within 10%, thereby verifying the testing technique. In general, the local distribution of erosion is concentrated in pits between three adjacent holes and trenches that join pits. The shapes of the pits and trenches are shown to be dependent upon operating conditions. Increases in beam current and the accel-grid voltage magnitude lead to deeper pits and trenches. Competing effects cause complex changes in depth-erosion rates as background pressure is increased. Shape factors that describe pits and trenches (i.e. ratio of the average erosion width to the maximum possible width) are also affected in relatively complex ways by changes in beam current, ac tel-grid voltage magnitude, and background pressure. In all cases, however, gross volumetric erosion rates agree with theoretical predictions.

Barker, Timothy↗
NASA NTRS1986

Predicted effect of dynamic load on pitting fatigue life for low-contact-ratio spur gears

How dynamic load affects the surface pitting fatigue life of external spur gears was predicted by using the NASA computer program TELSGE. Parametric studies were performed over a range of various gear parameters modeling low-contact-ratio involute spur gears. In general, gear life predictions based on dynamic loads differed significantly from those based on static loads, with the predictions being strongly influenced by the maximum dynamic load during contact. Gear mesh operating speed strongly affected predicted dynamic load and life. Meshes operating at a resonant speed or one-half the resonant speed had significantly shorter lives. Dynamic life factors for gear surface pitting fatigue were developed on the basis of the parametric studies. In general, meshes with higher contact ratios had higher dynamic life factors than meshes with lower contact ratios. A design chart was developed for hand calculations of dynamic life factors.

Lewicki, David G.↗
NASA NTRS2025

Large Impact Features on Ganymede and Callisto as Revealed By Geological Mapping and Morphometry

The icy Galilean satellites are host to a broad range of impact feature morphologies. Hypotheses seeking to explain the diversity of these impact features consider the effects of impact melt, the physical state of the subsurface at the time of impact, and the impactor characteristics. As part of a larger effort to assess the role of these factors in the formation and evolution of these impact features, we have performed topographic and geological mapping of 19 large impact features on Ganymede and Callisto. These are divided into two main morphological groups: craters (subdivided into pit, dome, and anomalous dome craters), and penepalimpsests/palimpsests. The transitions from pit, dome, to anomalous dome craters appear to be size-dependent up to diameters of ∼170 km. The morphologies of pit and dome craters appear to be independent of their age or geologic context. The impacts that formed them only affected a cold, rigid ice layer, with the development of pits and raised annuli on their floors possibly stemming from the evolution of a pocket of impact melt. The subdued rims and floors of anomalous dome craters indicate the increasing effect of a weak, warm ice layer on impact feature morphology with increasing size, but their prominent annuli and pits indicate that mobilization of impact melt is also a factor. The very low topographic relief of older penepalimpsests and palimpsests indicates that their impacts penetrated the ice shell to mobilize very large volumes of pre-existing liquid from a subsurface layer, with little contribution to the final feature morphology from impact melt. Penepalimpsests are distinguished from palimpsests by the higher frequency of concentric ridges within their interiors, indicating a generally more robust state of the subsurface that could better support the rotation and uplift of solid material during impact, even if a crater-like depression could not be supported. A few impact features seem to be transitional between anomalous dome craters and penepalimpsests, and the overlap of anomalous dome craters, penepalimpsests, and palimpsests in terms of diameter as well as age indicates that impactor size and subsurface properties over time are major factors in determining which of these morphologies emerges.

Oliver L White↗
NASA NTRS1997

ETP-0474: Evaluation of Electroless Nickel Coatings to Achieve Interference Fit in the RSRM Without Fretting

Part of the redesign of the SRMs for the Space Shuttle involved the substitution of three new capture cylinders for three of the previously used cylinders. These new cylinders mate with the old standard case segments in each of the three field joints. The new capture cylinders contain an integral capture latch on the tang end which mates with a case clevis during stackup at KSC. The capture cylinders also contain a groove in the capture latch to provide for a third 0-ring in the joint and are designed to achieve a metal-to- metal interference fit between the capture latch and the mating clevis. An unexpected fretting problem has occurred on the tang capture feature and the inner clevis leg interference fit surfaces on flight hardware since STS-26. Varying degrees of fretting damage have been found on the case segments from different flight motors. Fretting is a wear phenomena that occurs when two tightly fitting metal surfaces are subject to cyclic relative motion of extremely small amplitudes (generally less than 0.010-inch) in the absence of adequate lubrication. It is adhesive ("cold" - welding) in nature and vibration is its essential causative factor. This problem has manifested itself on the flight motors as a series of pits and axial gouges on the inside diameter (ID) surfaces of the inner clevis legs and the outside diameter (OD) surfaces of the tang capture features. The problem occurs in varying degrees of severity in all of the field joints. It is not believed that fretting is a flight safety issue. However, it could become a reusability issue if left unattended. Fretting has been encountered in other industries for many years and measures that will prevent or reduce it have been devised. These include: elimination or reduction of vibration (amplitudes and/or frequencies), elimination of slip, improved lubrication between parts, increased surface separation, increased interference, inducing residual compressive stresses in the surfaces of the mating parts, and employing non-fretting interference shims. Looking at each of these separately; vibration and slip occur in varying degrees and magnitudes in the field joints (as part of the roll-out, launch, flight, splashdown, flotation, and/or tow back) and are difficult to define or eliminate. Improved lubrication is something that was evaluated since it would be the simplest change to incorporate, but little or no improvement was found. Increasing surface separation would defeat the purpose of the interference fit. The effect of increasing the interference fit is unknown. Additional shot peening and/or surface rolling to impart residual compressive stresses in the joints undoubtedly would alter the characteristics and finish of the sealing surfaces of the motor cases. Also, experimental data' indicate that the tangs and clevises already have residual compressive stress fields on their surfaces yet fretting occurs. These stresses probably result from the case machining and the glass beading used to clean these surfaces.

Schaffnit, William O.↗
NASA NTRS1978

Temporal and spatial variations of the interplanetary dust flux

The heliocentric radial and latitudinal distributions of both small and large meteoritic particles appear to demonstrate that these particles have largely derived from comets in short-period orbits. Asteroids are unlikely to be a major source for the dust. There appears to be a spatial density depletion near the orbit of the earth, indicating significant control by the earth over particles or source bodies that come near it. Although many short-term fluctuations of meteoritic activity are observed, the content of the overall interplanetary meteoritic complex has probably been stable to within a factor of 2 within approximately the last 10,000 yr. This conclusion, together with meteoroid impact-pit and solar-flare track data on lunar rocks, suggests that solar flare activity may have been much higher about 10,000 yr ago than the present average rate.

Zook, H. A.↗
NASA NTRS1971

Martian environmental effects on solar cells and solar cell cover glasses

The results of a study concerned with the effects of the Martian environment on the performance of solar cells are given. The results indicate that the efficiency of a power system composed of solar cells will be greatly reduced when subjected to dust storms such as may occur on Mars. Two factors are responsible for this, (1) accumulation of dust on the protective covers, and (2) damage to covers by pitting, cracking, and chipping. It is recommended that this type of power system not be used on Mars landing vehicles. Experimental procedures are described and results are summarized and damage assessed.

Wade, F. A.↗
NASA NTRS2001

Evaluation of Ti-48Al-2Nb Under Fretting Conditions

An investigation was conducted to examine the fretting behavior of lambda-TiAl (Ti-48Al-2Cr-2Nb) in contact with a nickel-base superalloy (Inconel 718) in air at temperatures from 23 to 550 C. Fretting wear experiments were conducted with 9.4-mm-diameter hemispherical Inconel (IN) 718 pins in contact with Ti-48Al-2Cr-2Nb flats (and the reverse) at loads from 1 to 40 N and fretting frequencies from 50 to 160 Hz with slip amplitudes from 50 to 200 microns for 1 to 20 million fretting cycles. The results were similar for both combinations of pin and flat. Reference fretting wear experiments were also conducted with 9.4-mm-diameter hemispherical Ti-6Al-4V pins in contact with IN718 flats. The interfacial adhesive bonds between Ti-48Al-2Cr-2Nb and IN718 in contact were generally stronger than the cohesive bonds in the cohesively weaker Ti-48Al-2Cr-2Nb. The failed Ti-48Al-2Cr-2Nb subsequently transferred to the IN718 surface at any fretting condition. The wear scars produced on Ti-48Al-2Cr-2Nb contained metallic and oxide wear debris, scratches, plastically deformed asperities, cracks, and fracture pits. Oxide layers readily formed on the Ti-48Al-2Cr-2Nb surface at 550 C, but cracks easily occurred in the oxide layers. Factors including fretting frequency, temperature, slip amplitude, and load influenced the fretting behavior of Ti-48Al-2Cr-2Nb in contact with IN718. The wear volume loss of Ti-48Al-2Cr-2Nb generally decreased with increasing fretting frequency. The increasing rate of oxidation at elevated temperatures up to 200 C led to a drop in wear volume loss at 200 C. However, the fretting wear increased as the temperature was increased from 200 to 550 C. The highest temperatures of 450 and 550 C resulted in oxide film disruption with generation of cracks, loose wear debris, and pits on the Ti-48Al-2Cr-2Nb wear surface. The wear volume loss generally increased as the slip amplitude increased. The wear volume loss also generally increased as the load increased. Increasing slip amplitude and increasing load both tended to produce more metallic wear debris, causing severe abrasive wear in the contacting metals.

Miyoshi, Kazuhisa↗
NASA NTRS2015

Results of Lunar Impact Observations During Geminid Meteor Shower Events

Meteoroids are natural particles with origins from comets, asteroids, and planets from within the solar system. On average, 33 metric tons (73,000 lb) of meteoroids hit Earth everyday with velocities ranging between 20 and 72 km/s. However, the vast majority of these meteoroids disintegrate in the atmosphere and never make it to the ground. The Moon also encounters the same meteoroid flux, but has no atmosphere to stop them from striking the surface. At such speeds even a small meteoroid has incredible energy. A meteoroid with a mass of only 5 kg can excavate a crater over 9 m across, hurling 75 metric tons (165,000 lb) of lunar soil and rock on ballistic trajectories above the lunar surface. Meteoroids with particle sizes as small as 100 micrometer (1 Microgram) can do considerable damage to spacecraft in Earth's orbit and beyond. Impacts can damage thermal protection systems, radiators, windows, and pressurized containers. Secondary effects might include partial penetration or pitting, local deformation, and surface degradation that can cause a failure upon reentry. The speed, mass, density, and flux of meteoroids are important factors for design considerations and mitigation during operations. Lunar operations (unmanned and manned) are also adversely affected by the meteoroid flux. Ejecta from meteoroid impacts is also part of the lunar environment and must be characterized. Understanding meteoroid fluxes and the associated risk of meteoroids impacting spacecraft traveling in and beyond Earth's orbit is the objective of the Meteoroid Environment Office (MEO) located at Marshall Space Flight Center (MSFC). One of the MEO's programs is meteoroid impact monitoring of the Moon. The large collecting area of the night side of the lunar disk provides statistically significant counts of meteoroids that can provide useful information about the flux of meteoroids in the hundreds of grams to kilograms size range. This information is not only important for characterizing the lunar environment associated with larger lunar impactors, but also provides statistical data for verification and improving meteoroid prediction models. Current meteoroid models indicate that the Moon is struck by a sporadic meteoroid with a mass greater than 1 kg over 260 times per year. This number is very uncertain since observations for objects in this mass range are few. Factors of several times, higher or lower, are easily possible. Meteor showers are also present to varying degrees at certain times of the year. The Earth experiences meteor showers when encountering the debris left behind by comets, which is also the case with 2 the Moon. During such times, the rate of shower meteoroids can greatly exceed that of the sporadic background rate for larger meteoroids. Looking for meteor shower impacts on the Moon at about the same time as they occur on Earth will yield important data that can be fed into meteor shower forecasting models, which can then be used to predict times of greater meteoroid hazard on the Moon. The Geminids are one such meteor shower of interest. The Geminids are a major meteor shower that occur in December with a peak intensity occurring usually during the 13th and 14th of the month and appearing to come from a radiant in the constellation Gemini. The Geminids are interesting in that the parent body of the debris stream is an asteroid, which along with the Quadrantids, are the only major meteor showers not originating from a comet. The Geminids parent body, 3200 Phaethon, is about 5 km in diameter and has an orbit that has a 22deg inclination which intersects the main asteroid belt and has a perihelion less than half of Mercury's perihelion distance. Thus, its orbit crosses those of Mars, Earth, Venus, and Mercury. The Geminid debris stream is by far the most massive as compared to the others. When the Earth passes through the stream in mid-December, a peak intensity of approx. equal 120 meteors per hour can be seen. Because of the Geminids' relatively large intensity and unique origin, it is important to monitor and gain information about the Geminids so as to improve their forecasts and understand their contribution to the meteoroid environment in Earth's orbit and at the Moon. It is the purpose of this Technical Memorandum (TM) to document two lunar observing periods coinciding with the Geminid meteor showers that occurred in 2006 and 2010.

Suggs, R. J.↗
NASA NTRS1986

The abundance of interstellar sulphur and zinc in high density sight-lines

On the basis of early absorption line studies of individual lines of sight with the Copernicus satellite, chlorine, sulphur and zinc were classed together as elements which showed little or no depletion, relative to hydrogen, in the interstellar medium. The abundances of other less volatile elements, such as Fe and Mg were found to vary widely from one sight-line to another with gas-phase abundances in some cases being orders of magnitude below their solar counterparts. Detailed studies are reported of the depletion/density behavior of two other volatile elements which were previously considered to be virtually undepleted, S and Zn, using equivalent width data from both Copernicus and IUE observations. The results provide further evidence that the established dependence of depletion on n bar (H) extends to volatile elements and show that their use as tracers of metallicity, or for estimating hydrogen column densities, may lead to large errors in sight-lines through dense regions. It now appears that such elements may take part in the surface chemistry of grains and be important constituents of grain mantle material, although they probably do not contribute significantly to the bulk mass of grains. Due to the very similar atomic masses and ionization potentials of sulphur and phosphorous, the thermal velocity distributions of the singly ionized species of these elements in interstellar clouds should be very similar. However, a comparison of Doppler widths (b-values) derived for SIT and PIT in the same sight-lines from the Bohlin et al Copernicus equivalent width measurements has revealed an unexpected systematic discrepancy of a factor of approx. 1.7. This Discrepancy indicates that the normally adopted oscillators strengths of the PII lambda lambda 1153 and 1302 A lines may require revision.

Harris, A. W.↗
NASA NTRS1997

Process-Induced Morphological Defects in Epitaxial CVD Silicon Carbide

Silicon carbide (SiC) semiconductor technology has been advancing rapidly, but there are numerous crystal growth problems that need to be solved before SiC can reach its full potential. Among these problems is a need for an improvement in the surface morphology of epitaxial films that are grown to produce device structures. Various processes before and during epilayer growth lead to the formation of morphological defects observed in SiC epilayers grown on SiC substrates. In studies of both 6H and 4H-SiC epilayers, atomic force microscopy (AFM) and other techniques have been used to characterize SiC epilayer surface morphology. In addition to the well-known micropipe defect, SiC epilayers contain growth pits, triangular features (primarily) in 4H-SiC, and macro step due to step bunching. In work at NASA Lewis, it has been found that factors contributing to the formation of some morphological defects include: defects in the substrate bulk, defects in the substrate surface caused by cutting and polishing the wafer, the tilt angle of the wafer surface relative to the basal plane, and growth conditions. Some of these findings confirm results of other research groups. This paper presents a review of published and unpublished investigations into processes that are relevant to epitaxial film morphology.

Powell, J. A.↗
NASA NTRS2012

Lunar Floor-Fractured Craters: Classification, Distribution and Implications for Magmatism and Shallow Crustal Structure

Floor-fractured craters (FFCs) are a class of lunar craters defined by their distinctly shallow, often plate-like floors, and combinations of radial, con-centric, and polygonal floor-fractures; a variety of other interior features are often observed, such as moats, ridges, small dark-haloed pits, and patches of mare material. They were first classified by Schultz [1] , who recognized eight overall types of floor-fractured crater. These eight subtypes have widely differing appearances, a factor that could provide insight into formation mechanisms (different manifestations of the same mechanism, or indicators of varying formation mechanisms). Two formation mechanisms for FFCs were initially proposed: 1) magmatic intrusion [1], in which magma rising toward the surface in dikes encountered low-density breccia lenses beneath crater floors and spread laterally to form sills, raising and fracturing the crater floor. 2) viscous relaxation [2], in which the properties of the crust permitted viscous flow in the vicinity of the crater, causing long-wavelength relaxation of the topography and uplift and fracturing of the crater floor. Critical to distinguishing between these two end-member hypotheses and identifying others is a quantitative assessment of the topography of FFCs and knowledge of their regional and local settings. The purpose of this study is to use newly available Lunar Reconnaissance Orbiter (LRO) Lunar Orbiter Laser Altimeter (LOLA) altimeter and Lunar Reconnaissance Orbiter Camera (LROC) image data to provide an updated global catalog of the locations, classes, morphometric and morphologic characteristics of all lunar floor-fractured craters. We use the excellent 8-class system initially described in Schultz [1] as a starting point for classification and the enhanced LOLA/LROC data sets to examine and categorize all FFCs; we found evidence for a new FFC class, discernably different from the previously existing types. Our approach, and the global categorization of all FFCs, permits the spatial distribution of each FFC-subtype to be plotted and assessed allowing for further investigation into FFC formation mechanisms. Upon completion, the data set will be made available on our web site at http://www.planetary.brown.edu/html_pages/data.htm.

Jozwiak, L. M.↗
NASA NTRSDate not supplied

Buto Facula, Ganymede: Palimpsest Exemplar

The Galilean satellites with icy surfaces (Europa, Ganymede, Callisto) are host, among other things, to a variety of large impact features that are, if not unique to these bodies, rarely encountered on planetary and satellite surfaces in the Solar System. These features include impact basins with central pits, domed floors, and so-called "pene-palimpsests" and "palimpsests". The authors have conducted a multidisciplinary approach to study how these features formed. It is likely that the particular combination of geophysical factors and impactor characteristics that is shared by these satellites is responsible for these features. One component of this study has been to derive the topography of a number of these features, and then use these Digital Terrain Models (DTM) as a fundamental tool in producing facies maps of a range of these features for which adequate data exist. Here we present the analysis of Buto Facula, Ganymede.

Jeffrey Morgan Moore↗
NASA NTRS2007

Notch Fatigue Strength of a PM Disk Superalloy

New powder metallurgy (PM) disk superalloys, such as ME3, LSHR, and Alloy 10, have been developed in recent years which enable rim temperatures in turbine disk applications to approach 1300 F. Before these alloys can be utilized at 1300 F their long term durability must be ensured. One of the key requirements for disk rims is notch fatigue strength. This issue is extremely important and is a direct result of the blade attachment geometry employed at the disk rim. Further, the imposition of a dwell at maximum load, associated with take off and landing, can also affect notch fatigue strength. For these reasons a study has been undertaken to assess the notch dwell fatigue strength of a modern PM disk alloy through spin pit evaluation of a prototypical disk. The first element of this program involves screening potential heat treatments with respect to notch fatigue strength at 1300 F utilizing a conventional notch fatigue specimen with a stress concentration factor (K(sub t)) of 2 and a 90 sec dwell at peak load. The results of this effort are reported in this paper including the downselect of an optimal heat treatment, from a notch fatigue standpoint.

Gayda, John↗
NASA NTRS1993

The growth of small corrosion fatigue cracks in alloy 2024

The corrosion fatigue crack growth characteristics of small surface and corner cracks in aluminum alloy 2024 is established. The damaging effect of salt water on the early stages of small crack growth is characterized by crack initiation at constituent particle pits, intergranular microcracking for a less than 100 micrometers, and transgranular small crack growth for a micrometer. In aqueous 1 percent NaCl and at a constant anodic potential of -700 mV(sub SCE), small cracks exhibit a factor of three increase in fatigue crack growth rates compared to laboratory air. Small cracks exhibit accelerated corrosion fatigue crack growth rates at low levels of delta-K (less than 1 MPa square root of m) below long crack delta-K (sub th). When exposed to Paris regime levels of crack tip stress intensity, small corrosion fatigue cracks exhibit growth rates similar to that observed for long cracks. Results suggest that crack closure effects influence the corrosion fatigue crack growth rates of small cracks (a less than or equal to 100 micrometers). This is evidenced by similar small and long crack growth behavior at various levels of R. Contrary to the corrosion fatigue characteristics of small cracks in high strength steels, no pronounced chemical crack length effect is observed for Al by 2024 exposed to salt water.

Piascik, Robert S.↗
NASA NTRS2004

Electrochemical Impedance Spectroscopy of Alloys in a Simulated Space Shuttle Launch Environment

Type 304L stainless steel (304L SS) tubing is currently used in various supply lines that service the Orbiter at NASA's John F. Kennedy Space Center Launch Pads in Florida (USA). The atmosphere at the Space Shuffle launch site is very corrosive due to a combination of factors, such as the proximity of the Atlantic Ocean and the concentrated hydrochloric acid produced by the fuel combustion reaction in the solid rocket boosters. The acidic chloride environment is aggressive to most metals and causes severe pitting in many of the common stainless steel alloys such as 304L SS. Stainless steel tubing is susceptible to pitting corrosion that can cause cracking and rupture of both high-pressure gas and fluid systems. Outages in the systems where failures occur can impact the normal operation of the shuttle and launch schedules. The use of a more corrosion resistant tubing alloy for launch pad applications would greatly reduce the probability of failure, improve safety, lessen maintenance costs, and reduce downtime. A study which included ten alloys was undertaken to find a more corrosion resistant material to replace the existing 304L SS tubing. The study included atmospheric exposure at NASA's John F. Kennedy Space Center outdoor corrosion test site near the launch pads and electrochemical measurements in the laboratory which included DC techniques and electrochemical impedance spectroscopy (EIS). This paper presents the results from EIS measurements on three of the alloys: AL6XN (UN N08367), 254SMO (UNS S32l54), and 304L SS (UNS S30403). Type 304L SS was included in the study as a control. The alloys were tested in three electrolyte solutions which consisted of neutral 3.55% NaC1, 3.55% NaCl in O.1N HC1, and 3.55% NaCl in 1.ON HC1. The solutions were chosen to simulate environments that were expected to be less, similar, and more aggressive, respectively, than those present at the Space Shuttle launch pads. The results from the EIS measurements were analyzed to evaluate the corrosion susceptibility of the alloys and to predict the long-term corrosion performance of the subject materials. The results from the EIS measurements for the three alloys indicated that the higher-alloyed 254SMO and AL6XN exhibited a significantly improved resistance to corrosion than the 304L SS as the concentration of hydrochloric acid in the 3.55% NaC1 solution was increased. The polarization resistance values obtained from the EIS measurements were consistent with those from linear polarization measurements, and were indicative of the actual long-term corrosion performance of the alloys during a two-year atmospheric exposure study.

Calle, L. M.↗