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Corrosion of ferritic steels by molten lithium: Influence of competing thermal gradient mass transfer and surface product reactions

Description: An Fe-12Cr-1MoVW steel was exposed to thermally convective lithium for 6962 h. Results showed that the weight change profile of Fe-12Cr-1MoVW steel changed substantially as the maximum loop temperature was raised from 500 to 600/sup 0/C. Furthermore, for a particular loop experiment, changes in the structure and composition of the exposed surfaces did not reflect typical thermal gradient mass transfer effects for all elements: the surface concentration of chromium was often a maximum at intermediate temperatures, while nickel (present at low concentrations in the starting material) tended to be transported to the coldest part of the loop. Such data were interpreted in terms of a qualitative model in which there are different dominant reactions or the various constituents of the ferritic steels (surface product formation involving nitrogen and/or carbon and solubility-driven elemental transport). This competition among different reactions is important in evaluating overall corrosion behavior and the effects of temperature. The overall corrosion rate of the 12Cr-1MoVW steel was relatively low when compared to that for austenitic stainless steel exposed under similar conditions.
Date: October 1, 1987
Creator: Tortorelli, P.F.
Partner: UNT Libraries Government Documents Department

Corrosion of ferrous alloys exposed to thermally convective Pb-17 at. % Li

Description: A type 316 stainless steel thermal convection loop with type 316 stainless steel coupons and a Fe-9 Cr-1 Mo steel loop containing Fe-12 Cr-1 MoVW steel specimens circulated molten Pb-17 at. % Li at a maximum temperature of 500/sup 0/C. Specimens were exposed for greater than 6000 h. Mass loss and surface characterization data were compared for these two alloys. At any particular exposure time, the corrosion of type 316 stainless steel by Pb-17 at. % Li was more severe, and of a different type than that of similarly exposed Fe-12 Cr-1 MoVW steel. The austenitic alloy suffered nonuniform penetration and dissolution by the lead-lithium, whereas the Fe-12 Cr-1 MoVW steel tended to be more uniformly corroded. The presence of a ferritic layer on the type 316 stainless steel, and its susceptibility to spalling during specimen cleaning, were shown to be important in evaluating the data and in comparing corrosion losses for the type types of alloys. A model for the nonuniform penetration of type 316 stainless steel by Pb-17 at. % Li was suggested.
Date: January 1, 1986
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Compatibility of materials for use in liquid-metal blankets of fusion reactors

Description: A review of corrosion and environmental effects on the mechanical properties of austenitic and ferritic steels for use with liquid metals in fusion reactors is presented. The mechanisms and kinetics of the corrosion processes in liquid lithium and Pb-17Li systems are examined and their influence on degradation of structural material is discussed. Requirements for additional data are identified.
Date: November 1, 1983
Creator: Chopra, O.K. & Tortorelli, P.F.
Partner: UNT Libraries Government Documents Department

Compatibility of stainless steel with Pb-17 AT. % Li

Description: The corrosion of type 316 stainless steel and Sandvik HT9 by static Pb-17 at. % Li between 300 and 500/sup 0/C was studied. The resulting weight losses were significantly greater than those of these steels in lithium. The corrosive attack was very uniform, and the room-temperature tensile properties of the steels were unaffected by the exposure. The application of molten Pb-17 at. % Li as a tritium-breeding fluid in conjunction with ferrous alloys in a fusion reactor may be limited to 400/sup 0/C or below.
Date: January 1, 1982
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Liquid metal corrosion considerations in alloy development

Description: Liquid metal corrosion can be an important consideration in developing alloys for fusion and fast breeder reactors and other applications. Because of the many different forms of liquid metal corrosion (dissolution, alloying, carbon transfer, etc.), alloy optimization based on corrosion resistance depends on a number of factors such as the application temperatures, the particular liquid metal, and the level and nature of impurities in the liquid and solid metals. The present paper reviews the various forms of corrosion by lithium, lead, and sodium and indicates how such corrosion reactions can influence the alloy development process.
Date: January 1, 1984
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Thermal-gradient mass transfer in lithium-stainless steel systems

Description: The corrosion of type 316 stainless steel by flowing Li was studied as a function of time in thermal-convection loops. After a transient period, the corrosion rates were observed to be constant with time with values ranging from 10 to 20 mg/m/sup 2/ h. Preliminary analysis indicated that the corrosion rate is controlled by the diffusion of Fe through the liquid Li boundary layer. The deposition processes involved the formation of crystals of nearly pure Cr in the cold legs of the loops.
Date: January 1, 1979
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Corrosion of Fe-Cr-Mn alloys in thermally convective lithium

Description: A series of austenitic Fe-Cr-Mn steels was exposed to circulating lithium at temperatures up to 500/sup 0/C. Two groups of the alloys, which contained 12 to 30 wt % Mn and 2 to 20 wt % Cr, were sequentially exposed for periods greater than 3000 h in a type 316 stainless steel thermal convection loop. Mass transfer of manganese caused very large weight losses from the steels containing 30 wt % Mn. However, the actual magnitude of corrosion losses for alloys containing 12 to 20 wt % Mn was difficult to establish due to competing surface reactions involving chromium.
Date: January 1, 1986
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Corrosion of an Fe-12 Cr-1 Mo VW steel in thermally-convective lithium

Description: A thermal-convection loop of Fe-12 Cr-1 Mo VW steel circulated pure lithium between 500 and 350/sup 0/C for 10,088 h. Periodic weighings of coupons at different temperatures around the loop revealed small weight losses and corrosion rates. Surface analysis showed a relatively thin corrosion layer with an underlying carbide-free zone and some depletion of chromium from the hottest specimen. While some mass transfer of chromium and nickel was detected, this mechanism did not strongly influence the weight loss process as it does with austenitic steels. Therefore, it appeared that reactions with carbon and nitrogen must be the dominant corrosion processes such that weight loss was maximized at the lowest temperature (350/sup 0/C). Overall, the lithium-steel reactions in the temperature range of this experiment were relatively sluggish and the corrosion was not severe.
Date: January 1, 1983
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Mass transfer behavior of a modified austenitic stainless steel in lithium

Description: An austenitic stainless steel that was developed to resist neutron damage was exposed to lithium in the high-temperature part of a thermal convection loop for 6700 h. Specimens of this Prime Candidate Alloy (PCA) composed of 65.0 Fe-15.9 Ni-13.0 Cr-1.9 Mo-1.9 Mn-1.7 Si-0.5 Ti-0.05 C (wt %) were exposed at 600 and 570/sup 0/C in both solution annealed and cold worked forms. The dissolution process was found to be similar to other austenitic alloys in flowing lithium: weight losses of PCA eventually became linearly proportional to exposure time with the specimen surfaces exhibiting porous layers depleted in nickel and chromium. However, the measured weight losses and dissolution rates of these PCA specimens were higher than those of type 316 stainless steel exposed under similar conditions and can be attributed to the higher nickel concentration of the former alloy. The effect of cold work on dissolution rates was less definitive, particularly at 570/sup 0/C. At longer exposure times, the annealed PCA specimen exposed at 600/sup 0/C suffered greater dissolution than the cold worked material, while no effect of prior deformation was observed by analysis of the respective surfaces.
Date: January 1, 1983
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Mass transfer deposits in lithium-type 316 stainless steel thermal-convection loops

Description: In spatially nonisothermal flowing liquid metal systems, selected constitutents of the containment materials characteristically dissolve into the liquid metal in the hotter zones and are deposited in the colder areas. The accumulation of deposits is often a more serious problem than dissolution because of attendant flow restrictions and, in reactor applications, the aggregation of radioactive species in the coolant circuits. Accordingly, the deposition processes in lithium-type 316 stainless steel thermal convection loops is studied. The morphology and composition of deposits varied with loop operating time. Initially, chromium-rich dendritic crystals formed in the colder region of a loop, but later the deposits changed in structure and contained significant amounts of nickel and iron. Deposition rates were also measured as a function of time and temperature and were correlated with the above observations. A plug extracted from one loop consisted of an aggregate of chromium-rich crystals.
Date: January 1, 1980
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Corrosion of type 316 stainless steel in molten LiF-LiCl-LiBr

Description: The properties of LiF-LiCl-LiBr salt make it attractive as a solvent for extracting tritium from a fusion reactor lithium blanket. Consequently, the corrosion of type 316 stainless steel by flowing (about 15 mm/s) LiF-LiCl-LiBr at a maximum temperature of 535/sup 0/C was studied to determine whether compatibility with the structural material would be limiting in such a system. The corrosion rate was found to be low (<2 ..mu..m/year) except immediately after the addition of a small amount of lithium metal to the salt. The lithium addition increased the corrosion rate to approx. 13.5 ..mu..m/year at 535/sup 0/C (approximately that of type 316 stainless steel exposed to lithium flowing at a similar velocity). At the proposed operating temperature (less than or equal to approx. 535/sup 0/C), however, it appears that type 316 stainless steel has acceptable compatibility with the tritium-processing salt LiF-LiCl-LiBr for use with a lithium blanket.
Date: January 1, 1981
Creator: Tortorelli, P.F.; DeVan, J.H. & Keiser, J.R.
Partner: UNT Libraries Government Documents Department

Mechanically reliable scales and coatings

Description: As the first stage in examining the mechanical reliability of protective surface oxides, the behavior of alumina scales formed on iron-aluminum alloys during high-temperature cyclic oxidation was characterized in terms of damage and spallation tendencies. Scales were thermally grown on specimens of three iron-aluminum composition using a series of exposures to air at 1000{degrees}C. Gravimetric data and microscopy revealed substantially better integrity and adhesion of the scales grown on an alloy containing zirconium. The use of polished (rather than just ground) specimens resulted in scales that were more suitable for subsequent characterization of mechanical reliability.
Date: July 1, 1995
Creator: Tortorelli, P.F. & Alexander, K.B.
Partner: UNT Libraries Government Documents Department

Influence of compositional modifications on the corrosion of iron aluminides of molten nitrate salts

Description: The corrosion of iron-aluminum alloys by molten nitrate salt as a function of aluminum, chromium, and other minor elements has been studied as part of an alloy design effort aimed at the development of a strong, ductile, corrosion-resistant FeAl type of aluminide. Short- term weight change data were used to examine the compositional dependence of the corrosion processes that occurred upon exposure of iron aluminides to highly oxidizing nitrate salts of 650{degrees}C. Corrosion resistance was found to increase with increasing aluminum concentrations of the alloy up to approximately 30 at. % Al. Chromium additions to the aluminide were not detrimental and may have improved the corrosion behavior for certain aluminum concentrations. No effects of minor alloying additions (C, B, Ti, and Zr) could be determined. The best overall corrosion resistance as measured by weight change results were obtained for an Fe-35.8 at. % Al aluminide containing some chromium. Based on linear weight loss kinetics, the weight change measurements for the most resistant compositions predict corrosion rates of 300 {mu}m/year or less at 650{degrees}C. These rates are substantially better than typical nickel-based alloys and stainless steels. From a consideration of the weight changes; the microstructural, thermodynamic, and X-ray diffraction data; and the salt analyses, corrosion of iron aluminides by the molten nitrate salt appears to be controlled by oxidation of base metal components and a slow release of material from an aluminum-rich product layer into the salt. The rate of release was substantially lower than that previously found for iron and iron-based alloys. This would imply that corrosion of iron aluminides could be minimized by maximizing the surface coverage of this aluminum-rich layer either by alloying or by an appropriate preoxidation treatment.
Date: January 1, 1991
Creator: Tortorelli, P.F. & Bishop, P.S.
Partner: UNT Libraries Government Documents Department

Corrosion in lithium-stainless steel thermal-convection systems

Description: The corrosion of types 304L and 316 austenitic stainless steel by flowing lithium was studied in thermal-convection loops operated at 500 to 650/sup 0/C. Both weight and compositional changes were measured on specimens distributed throughout each loop and were combined with metallographic examinations to evaluate the corrosion processes. The corrosion rate and mass transfer characteristics did not significantly differ between the two austenitic stainless steels. Addition of 500 or 1700 wt ppM N to purified lithium did not increase the dissolution rate or change the attack mode of type 316 stainless steel. Adding 5 wt % Al to the lithium reduced the weight loss of this steel by a factor of 5 relative to a pure lithium-thermal-convection loop.
Date: January 1, 1980
Creator: Tortorelli, P.F.; DeVan, J.H. & Selle, J.E.
Partner: UNT Libraries Government Documents Department

The effect of microstructure and temperature on the oxidation behavior of two-phase Cr-Cr{sub 2}X (X = Nb, Ta) alloys

Description: The oxidation behavior of Cr(X) solid solution (Cr{sub ss}) and Cr{sub 2}X Laves phases (X = Nb, Ta) was studied individually and in combination at 950--1,100 C in air. The Cr{sub ss} phase was significantly more oxidation resistant than the Cr{sub 2}X Laves phase. At 950 C, two-phase alloys of Cr-Cr{sub 2}Nb and Cr-Cr{sub 2}Ta exhibited in-situ internal oxidation, in which remnants of the Cr{sub 2}X Laves phase were incorporated into a growing chromia scale. At 1,100 C, the Cr-Cr{sub 2}Nb alloys continued to exhibit in-situ internal oxidation, which resulted in extensive O/N penetration into the alloy ahead of the alloy-scale interface and catastrophic failure during cyclic oxidation. IN contrast, the Cr-Cr{sub 2}Ta alloys exhibited a transition to selective Cr oxidation and the formation of a continuous chromia scale. The oxidation mechanism is interpreted in terms of multiphase oxidation theory.
Date: November 1, 1998
Creator: Brady, M.P. & Tortorelli, P.F.
Partner: UNT Libraries Government Documents Department

Metal filter materials in combustion environments

Description: Hot gas filtration in pressurized fluidized bed combustion (PFBC) systems has been proven below 750 C (1400 F). Advanced PFBC designs, focused on operational and efficiency improvements, will require filtration at higher temperatures. E.g., in first-generation advanced PFBCs, the filters will have to perform at 870 C (1600 F), while second-generation units, with both carbonizers for fuel-gas production and fluidized-bed combustors, will eventually require filters to operate up to 930 and 870 C (1700 and 1600 F). Results from the final test campaign at the Tidd PFBC Demonstration Project showed that at these higher temperatures, ceramic filter reliability may be problematical, so it will be of interest to re-examine the possibility of using advanced metal hot-gas filters for these advanced PFBC applications in view of the exceptional corrosion resistance of Fe aluminides in high-temperature sulfur-bearing atmospheres. For the second-generation PFBCs, performance criteria for the carbonizer filters are essentially the same as those for integrated gasification combined cycle systems (reducing environments). For the combustor, issues are similar to those of advanced first-generation units (oxidizing) except that the fuel (byproduct char from carbonizer) should be somewhat clearer and filter performance requirements less demanding than for PFBC systems such as the Tidd plant. For the carbonizer system, the nearer term (market entry) goals are to develop filter materials that will perform at 650-760 C (1200-1400 F), with an increase to 800-930 C (1500-1700 F) for improved cycle efficiency.
Date: September 1, 1996
Creator: Judkins, R.R.; Tortorelli, P.F. & Wright, I.G.
Partner: UNT Libraries Government Documents Department

Elevated temperature static fatigue of a Nicalon fiber-reinforced SiC composite

Description: Static fatigue tests of a Nicalon fiber-reinforced SiC matrix composite were conducted in four-point bending over a temperature range of 425 to 1,150 C in air at selected stress levels. The composite consisted of a Nicalon cloth with a 0.3 {mu}m graphite interfacial coating and a Forced Chemical Vapor Infiltration (FCVI) SiC matrix composite; samples were tested with or without a final protective SiC seal coat. The results indicated that the fatigue life of the Nicalon-SiC composite decreased with an increase in either applied stresses or test temperatures. However, the composite exhibited a fatigue limit of {approximately} 100 MPa at temperatures < 950 C which decreased to {approximately} 70 MPa at 1,150 C. Both electron microscopy and thermogravimetric studies suggested that the lifetime of the composites was dictated by the oxidation of graphite interfacial layer at temperatures {le} 700 C and by oxidation of graphite coating accompanied by formation of silicate interfacial layer via oxidation of the Nicalon fiber (and the SiC matrix) at temperatures {ge} 950 C. Use of a SiC seal coat effectively retarded the oxidation reactions and increased the lifetime by at least one order of magnitude at 425 C. On the other hand, the SiC seal coat made little (if any) difference in fatigue life at 950 C.
Date: December 31, 1994
Creator: Lin, H.T.; Becher, P.F. & Tortorelli, P.F.
Partner: UNT Libraries Government Documents Department

High-temperature oxidation/sulfidation resistance of iron-aluminide coatings

Description: Iron aluminides containing > 20-25 at. % Al have oxidation and sulfidation resistance at temperatures well above those at which these alloys have adequate mechanical strength. Accordingly, these alloys may find application as coatings or claddings on more conventional higher-strength materials which are generally less corrosion-resistant at high temperatures. To this end, iron-aluminide coatings were prepared by gas tungsten arc and gas metal arc weld-overlay techniques. Specimens were cut from weld deposits and exposed to a highly aggressive oxidizing-sulfidizing (H2S-H2-H2O-Ar) environment at 800 C. All the weld overlayers showed good corrosion behavior under isothermal conditions, including a gas metal arc-produced deposit with only 21 at. % Al. Rapid degradation in corrosion resistance was observed under thermal cycling conditions when the initally grown scales spalled and the rate of reaction was then not controlled by formation of slowly growing Al oxide. Higher starting Al concentrations (> {approximately} 25 at. %) are needed to assure overall oxidation-sulfidation resistance of the weld overlays, but hydrogen cracking susceptibility must be minimized in order to physically separate the corrosive species from the reactive substrate material.
Date: April 1, 1996
Creator: Tortorelli, P.F.; Wright, I.G.; Goodwin, G.M. & Howell, M.
Partner: UNT Libraries Government Documents Department

The oxidation behavior of iron aluminides at 1300{degrees}C

Description: The oxidation behavior of iron-aluminum alloys, in air and oxygen, at 1300{degrees}C has been studied with particular emphasis on the time to loss of protectiveness with onset of breakaway attack. The role of alloy aluminum content between 8.4 and 15.8 w/o and of the addition of a reactive element, zirconium, up to 0.2 w/o, were examined. The periods over which the oxide scales remained protective were quantitatively correlated with aluminum depletion in the alloy substrate. Times to the onset of breakaway for Fe{sub 3}Al-Zr have been compared with those for commercial ODS FeCrAl alloys containing Y{sub 2}O{sub 3} (MA 956, PM 2000, ODM 751). Characterization of the oxidation of the Fe3Al-Zr alloys was undertaken using a range of surface analytical procedures, including x-ray diffraction, optical microscopy, scanning and scanning transmission electron microscopy with associated energy dispersive x-ray spectroscopy, and electron microprobe analysis.
Date: November 1, 1996
Creator: Bennett, M.J.; DeVan, J.H. & Tortorelli, P.F.
Partner: UNT Libraries Government Documents Department

Oxidation behavior of Cr-Cr{sub 2}Nb alloys

Description: Oxidation of hypoeutectic Cr-Cr{sub 2}Nb alloys containing 6 and 12% Nb at 950 C resulted in formation of a multiproduct scale consisting of a continuous Cr{sub 2}O{sub 3} outer layer and an inner region of discrete CrNbO{sub 4} products interspersed with Cr{sub 2}O{sub 3}. Overall oxidation behavior resembled that of Cr as reactions with the Cr-rich phase tended to dominate. Oxidation resistance, in terms of reaction kinetics and scale adherence, increased with increasing volume fraction of the Cr-Cr{sub 2}Nb eutectic phase. A model for the oxidation of these alloys based on the growth of Cr{sub 2}O{sub 3} on the Cr-rich matrix regions and the formation of a slower growing CrNbO{sub 4} on the Cr{sub 2}Nb-enriched phase can qualitatively explain the development of the multiproduct scale and the observed gravimetric and spallation results. Possible microstructural/compositional modifications to improve oxidation resistance are suggested.
Date: December 31, 1996
Creator: Tortorelli, P.F. & Pint, B.A.
Partner: UNT Libraries Government Documents Department

High-temperature corrosion and applications of nickel and iron aluminides in coal-conversion power systems

Description: Nickel and iron aluminide intermetallics are being developed for use as structural materials and/or as cladding for conventional engineering alloys. In addition to strength advantages, these materials exhibit excellent resistance to corrosion in single- and multioxidant environments at elevated temperatures by the formation of slow-growing, adherent alumina scales. Corrosion resistance in a given environment is strongly dependent on the composition of the alloy and on the nature of the corrosive species prevalent in the service environment. This paper presents a comprehensive review of the current status of the corrosion performance of these intermetallics in oxidizing, sulfidizing, and multicomponent gas environments of typical coal-conversion systems. Mechanisms of scale development/breakdown, performance envelopes for long-term usage of these materials, approaches to modifying the surfaces of engineering alloys by cladding or coating them with intermetallics, and in-service experience with these materials are emphasized.
Date: October 1, 1996
Creator: Natesan, K. & Tortorelli, P.F.
Partner: UNT Libraries Government Documents Department

High temperature corrosion behavior of iron-aluminide alloys and coatings

Description: The long-term oxidation performance of ingot- and powder-processed Fe-28 at.% Al-(2--5)% Cr alloys with minor oxygen-active element or oxide additions was characterized for exposures in air at 1,000--1,300 C. Additions of zirconium or yttria substantially improved the adhesion of alumina scales grown on iron aluminides. At lower temperatures, the ingot-processed alloys performed similarly to ODS Fe{sub 3}Al alloys and other alumina-formers. However, at 1,200 and 1,300 C, the oxidation resistance of the ingot-processed Fe{sub 3}Al was degraded due to deformation of the substrate and some localized reaction product growth. Other oxidation experiments showed that the addition of an oxide dispersion to iron aluminides reduced the critical aluminum concentration for protective alumina scale formation. Oxide-dispersion-strengthened Fe{sub 3}Al alloys made from commercially prepared powders and an iron-aluminide coating with 21% Al and 1% Cr, prepared by a gas metal arc weld-overlay techniques, showed excellent oxidation/sulfidation resistance.
Date: August 1, 1997
Creator: Tortorelli, P.F.; Pint, B.A. & Wright, I.G.
Partner: UNT Libraries Government Documents Department

Interface oxidation and stress-rupture of Nicalon{trademark}/SiC CFCCs at intermediate temperatures

Description: The effect of oxidation of the carbonaceous fiber coating on the intermediate temperature stress-rupture behavior of a Nicalon{trademark}/C/SiC continuous fiber composite was modeled. The model, that was reduced to the analysis of a general ideal bundle composed of classical fibers subjected to constant loading, predicts that the oxidation of the fiber coating triggers a sequence of processes that can lead, under certain conditions, to composite failure. These processes involve loss of stress transfer between the fiber and the matrix, fiber overloading, and fiber failure. The implications of the model predictions are discussed in relation to experimental measurements at 425 C in air that show that Nicalon{trademark}/C/SiC exhibits time-dependent loss of strength.
Date: October 1, 1996
Creator: Lara-Curzio, E.; Ferber, M.K. & Tortorelli, P.F.
Partner: UNT Libraries Government Documents Department

The microstructure and mechanical reliability of alumina scales and coatings

Description: Alumina scales on iron-aluminides (Fe{sub 3}Al-based) and NiCrAl- based alloys were characterized in order to develop the knowledge to control the oxidation performance of alloys by controlling the microstructure and microchemistry of their scales. Plasma-deposited amorphous alumina coatings on iron-aluminides were used to study phase transformations, transport processes in the scales, and S segregation to the scale/metal interface. It was found that during heat treatment in absence of oxidation, amorphous coatings first transform to {gamma}-Al{sub 2}O{sub 3} and eventually {alpha}-Al{sub 2}O{sub 3} nucleates at the scale/metal interface. Sulfur from the Zr- free alloy segregates to the scale/metal interface during heat treatment. Thermally grown scales on Zr-doped iron-aluminides were compared to those formed after oxidation of a specimen with an alumina coating. Microstructural and gravimetric results showed that the primarily amorphous alumina coating promoted the nucleation and growth of metastable alumina phases, which resulted in more rapid oxidation. The thermally grown oxide was found on top of the coating. The NiCrAl-based alloys formed columnar alumina scales underneath a layer of mixed oxides. Segregation of alloying elements like Y, Hf, and At was found at both oxide grain boundaries and scale/metal interfaces.
Date: September 1, 1997
Creator: Alexander, K.B.; Pruessner, K. & Tortorelli, P.F.
Partner: UNT Libraries Government Documents Department