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Results for “Oxidation Penetration”

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
DOE OSTI2024

Oxidation Penetration in Nuclear Graphite

Study results are presented for seven grades of graphite where 21 cylindrical samples were oxidized to a nominal level of mass loss. Low mass loss samples exhibited ~3% oxidative mass loss, intermediate ~8%, and high ~11%. Flat sample surfaces were covered during oxidation to minimize oxidation penetration at the top and bottom of each sample. Oxidized samples had their diameters reduced stepwise in 1 mm or 2 mm increments. Residual samples were weighed, geometric dimensions were recorded, and Archimedes measurements were taken at each step. Preliminary comparative graphical analysis is presented to illustrate the resultant density gradients observed. Raw tabular data are also provided.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1988

Grain boundary oxidation and low-cycle fatigue at elevated temperatures

Fatigue life consists of fatigue crack nucleation and propagation periods. In order to predict fatigue life accurately, a methodology for the quantitative assessment of these two fatigue damage processes had to be devised. Grain boundary oxidation penetrates faster than does oxidation within a grain. This faster oxidation penetration causes intergranular fatigue failures at elevated temperatures. Grain boundary oxidation accelerates both crack nucleation and propagation. Grain boundary oxidation kinetics and the statistical distribution of grain boundary oxide penetration depth were measured. Quantitative applications of the grain boundary oxidation kinetics to fatigue crack nucleation and propagation were analyzed. A method, based on the Weibull distribution, of extrapolating the laboratory oxidation data measured with small samples to large engineering structures is presented.

Liu, H. W.↗
NASA NTRS1986

Grain boundary oxidation and an analysis of the effects of pre-oxidation on subsequent fatigue life

The effects of preoxidation on subsequent fatigue life were studied. Surface oxidation and grain boundary oxidation of a nickel-base superalloy (TAZ-8A) were studied at 600 to 1000 C for 10 to 1000 hours in air. Surface oxides were identified and the kinetics of surface oxidation was discussed. Grain boundary oxide penetration and morphology were studied. Pancake type grain boundary oxide penetrates deeper and its size is larger, therefore, it is more detrimental to fatigue life than cone-type grain boundary oxide. Oxide penetration depth, a (sub m), is related to oxidation temperature, T, and exposure time, t, by an empirical relation of the Arrhenius type. Effects of T and t on statistical variation of a (sub m) were analyzed according to the Weibull distribution function. Once the oxide is cracked, it serves as a fatigue crack nucleus. Statistical variation of the remaining fatigue life, after the formation of an oxide crack of a critical length, is related directly to the statistical variation of grain boundary oxide penetration depth.

Oshida, Y.↗
NASA NTRS1988

Grain boundary oxidation and an analysis of the effects of oxidation on fatigue crack nucleation life

The effects of preoxidation on subsequent fatigue life were studied. Surface oxidation and grain boundary oxidation of a nickel-base superalloy (TAZ-8A) were studied at 600 to 1000 C for 10 to 1000 hours in air. Surface oxides were identified and the kinetics of surface oxidation was discussed. Grain boundary oxide penetration and morphology were studied. Pancake type grain boundary oxide penetrates deeper and its size is larger, therefore, it is more detrimental to fatigue life than cone-type grain boundary oxide. Oxide penetration depth, a (sub m), is related to oxidation temperature, T, and exposure time, t, by an empirical relation of the Arrhenius type. Effects of T and t on statistical variation of a (sub m) were analyzed according to the Weibull distribution function. Once the oxide is cracked, it serves as a fatigue crack nucleus. Statistical variation of the remaining fatigue life, after the formation of an oxide crack of a critical length, is related directly to the statistical variation of grain boundary oxide penetration depth.

Oshida, Y.↗
NASA NTRS1986

Grain boundary oxidation and oxidation accelerated fatigue crack nucleation and propagation

Fatigue life at elevated temperatures is often shortened by oxidation. Grain boundary oxidation penetrates deeper than the surface oxidation. Therefore, grain boundary oxide penetration could be the primary cause of accelerated fatigue crack nucleation and propagation, and the shortened fatigue life at elevated temperatures. Grain boundary oxidation kinetics was studied and its statistical scatter was analyzed by the Weibull's distribution function. The effects of grain boundary oxidation on shortened fatigue life was analyzed and discussed. A model of intermittent microruptures of the grain boundary oxide was proposed for the fatigue crack growth in the low frequency region. The proposed model is consistent with the observations that fatigue crack growth rate in the low frequency region with hold time at K sub max is inversely proportional to cyclic frequency and that crack growth is intergranular.

Liu, H. W.↗
DOE OSTI2025

Deformation band corrosion as a result of applied stress and cold-work in 304 stainless steel in simulated pressurized water reactor primary water conditions

Stainless steels like 304SS are commonly used in pressurized water reactor primary water environments due to their excellent resistance to stress corrosion cracking (SCC). However, SCC susceptibility has been observed in cold-worked 304SS. Cold-rolling introduces a high density of defects, such as deformation bands or dislocations, into the microstructure; applied stress, even if macroscopically below the yield stress, can result in regions with high localized stresses. Cold-worked and non-cold-worked samples were exposed to 360 °C simulated PWR primary water for 1500 h with and without active loading. Corrosion susceptibility of dislocations and deformation bands induced by cold-rolling and/or applied stress was studied using high-resolution (analytical) transmission electron microscopy. Deformation bands were generated in all specimens examined in the study. Penetrative oxidation was observed in some deformation bands in each specimen. The depth of penetrative deformation band oxidation frequently exceeded the depth of grain boundary oxidation in all specimens. However, deformation band oxides generally were narrowly confined to the deformation band plane. Highly Ni-rich regions were observed beyond all oxidation fronts. Surface oxides were thicker in the specimens exposed under active loading. In conclusion, the implications of these findings at surfaces for deformation bands intersecting stress corrosion crack paths are discussed.

EFTEM↗
NASA NTRS1986

Grain boundary oxidation and its effects on high temperature fatigue life

Fatigue lives at elevated temperatures are often shortened by creep and/or oxidation. Creep causes grain boundary void nucleation and grain boundary cavitation. Grain boundary voids and cavities will accelerate fatigue crack nucleation and propagation, and thereby shorten fatigue life. The functional relationships between the damage rate of fatigue crack nucleation and propagation and the kinetic process of oxygen diffusion depend on the detailed physical processes. The kinetics of grain boundary oxidation penetration was investigated. The statistical distribution of grain boundary penetration depth was analyzed. Its effect on high temperature fatigue life are discussed. A model of intermittent micro-ruptures of grain boundary oxide was proposed for high temperature fatigue crack growth. The details of these studies are reported.

Liu, H. W.↗
NASA NTRS1986

Grain boundary oxidation and fatigue crack growth at elevated temperatures

Fatigue crack growth rate at elevated temperatures can be accelerated by grain boundary oxidation. Grain boundary oxidation kinetics and the statistical distribution of grain boundary oxide penetration depth were studied. At a constant delta K-level and at a constant test temperature, fatigue crack growth rate, da/dN, is a function of cyclic frequency, nu. A fatigue crack growth model of intermittent micro-ruptures of grain boundary oxide is constructed. The model is consistent with the experimental observations that, in the low frequency region, da/dN is inversely proportional to nu, and fatigue crack growth is intergranular.

Liu, H. W.↗
NASA NTRS1986

Grain boundary oxidation and fatigue crack growth at elevated temperatures

Fatigue crack growth rate at elevated temperatures can be accelerated by grain boundary oxidation. Grain boundary oxidation kinetics and the statistical distribution of grain boundary oxide penetration depth were studied. At a constant delta K-level and at a constant test temperature, fatigue crack growth rate, da/dN, is a function of cyclic frequency, nu. A fatigue crack growth model of intermittent micro-ruptures of grain boundary oxide is constructed. The model is consistent with the experimental observations that, in the low frequency region, da/dN is inversely proportional to nu, and fatigue crack growth is intergranular.

Liu, H. W.↗
DOE OSTI2024

Graphite Oxidation Activities

Graphite Oxidation Activities to include introduction, rate determination, strength after oxidation, penetration depth analysis, strategic partnership projects, and summary and continuing work.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1982

O-18 tracer studies of Al2O3 scale formation on NiCrAl alloys

Diffusion processes in Al2O3 scales formed on NiCrAl + Zr alloys were studied by the proton activation technique employing the O-18 isotope as a tracer. The O-18 profiles identified a zone of oxide penetration beneath the external scale. Both this subscale formation and the outer Al2O3 scale thickness were shown by this technique to increase with Zr content in the alloy. Estimated kp's from scale thicknesses were in agreement with gravimetric measurements for various Zr levels. Alternate exposures in O-16 and O-18 revealed that oxygen inward transport was the primary growth mechanism. A qualitative analysis of these O-18 profiles indicated that the oxygen transport was primarily via short-circuit paths, such as grain boundaries.

Reddy, K. P. R.↗
NASA NTRS1955

Engine Performance of Precision-forged, Electropolished and Machined Blades of Nimonic 80 and 80A Alloys

An investigation was conducted to determine the effect of electropolishing precision-forged blades and of machining blades from oversize forgings on the engine performance of Nimonic 80 and Nimonic 80A turbine blades. These blades, along with precision-forged blades, were run in a J33-9 turbojet engine. The tests resulted in the following conclusions: (1) Electropolishing of precision-forged blades did not improve engine life relative to the life of nonelectropolished blades. (2) Machining blades from oversize forgings did not improve the engine life of precision-forged blades. (3) The precision-forging and heat-treating practice used in fabricating the blades investigated was such that the surface roughness and oxide penetration was so slight, approximately 0.0005 inch in depth, as to preclude any benefits derived from surface removal by electropolishing or machining.

Sikora, Paul F↗
NASA NTRS1990

High temperature reactions of ceramics and metals with chlorine and oxygen

The reactions of chlorine and oxygen with solids are complex and quite dependent on material and reaction conditions. However, there are four reaction schemes that describe many of these reactions. These are direct reaction of chlorine with the oxide layer, penetration of the oxide layer by chlorine, paralinear behavior where oxidation and chlorination are of comparable rates, and finally, gas phase reactions where the volatile chlorides react with oxygen. Examples of chlorine and oxygen reactions with cobalt, nickel, chromium, molybdenum, and silicon carbide illustrate each of these four reaction schemes.

Jacobson, N. S.↗
NASA NTRS1977

Thermionic converter performance with oxide collectors

Thermionic converters using a variety of metal oxide collector surfaces have been fabricated and tested. Both work function and power output data are presented and evaluated. Oxides of barium, strontium, zinc, tungsten and titanium have been incorporated into a variable spacing converter. Tungsten oxide was found to give the highest converter performance and to furnish oxygen for the emitter at the same time. Oxygenated emitters operate at reduced cesium pressure with an increase in electrode spacing. Electron spectroscopy for chemical analysis (ESCA) performed on several tungsten oxide collectors showed cesium penetration of the oxide layer, possibly forming a cesium tungstate bronze. Titanium oxide showed high performance but did not furnish oxygen for the emitter; strontium oxide, in the form of a sprayed layer, appeared to dissociate in the presence of cesium. Sprayed coatings of barium and zinc oxides produced collector work functions of about 1.3 eV, but had excessive series resistance. Lanthanum hexaboride, in combination with oxygen introduced through a silver tube, and cesium produced a low work function collector and better than average performance.

Lieb, D.↗
NASA NTRS1973

Detection of lack of fusion using opaque additives

Reliable nondestructive inspection for incomplete weldment penetration and rapid oxidation of aluminum surfaces when exposed to the atmosphere are currently two major problems in welded aluminum spacecraft structure. Incomplete-penetration defects are extremely difficult to detect and can lead to catastrophic failure of the structure. The moisture absorbed by aluminum oxide on the surface can cause weldment porosity if the surface is not cleaned before welding. The approach employed in this program to solve both problems was to employ copper as a coating to prevent oxidation of the aluminum. Also, copper was used as an opaque additive in the weldment to enhance X-ray detection in the event of incomplete penetration.

Cook, J. L.↗
NASA NTRS1973

Study of meteoroid detection systems applicable to the outer planets missions

Modifications to the Pioneer 10/11 meteoroid detection experiment to allow it to be used for outer planet missions were investigated. Both pressurized cells and metal-oxide silicon (MOS) penetration detectors are considered. Both the sensors systems and the electronics are treated. Investigation of the calibration and characterization of the MOS penetration detector is reported.

Brooks, A. D.↗