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Galvanic corrosion study of container materials using zero resistance ammeter

Description: Galvanic corrosion behavior of A 516 steel separately coupled to six different corrosion-resistant alloys was investigated in an acidic brine (pHa2.70) at 30{degree}C 60{degree}C and 80{degree}C using zero resistance ammeter technique. The corrosion-resistant alloys include Alloys 825, G-3, G-30, C-4 and C-22; and Ti Grade-12, which were coupled to A 516 steel at an anode-to- cathode area ratio of one. The galvanic current and galvanic potential were measured as a function of time at all three temperatures. Optical microscopic examination was also performed on all tested specimens to evaluate the extent of surface degradation due to galvanic coupling. The overall results are presented in this paper.
Date: November 1, 1997
Creator: Roy, A. K., LLNL
Partner: UNT Libraries Government Documents Department

Modeling of stresses at grain boundaries with respect to occurrence of stress corrosion cracking

Description: The distributions of elastic stresses/strains in the grain boundary regions were studied by the analytical and the finite element models. The grain boundaries represent the sites where stress concentration occurs as a result of discontinuity of elastic properties across the grain boundary and the presence of second phase particles elastically different from the surrounding matrix grains. A quantitative analysis of those stresses for steels and nickel based alloys showed that the stress concentrations in the grain boundary regions are high enough to cause a local microplastic deformation even when the material is in the macroscopic elastic regime. The stress redistribution as a result of such a plastic deformation was discussed.
Date: December 31, 1995
Creator: Kozaczek, K. J.; Sinharoy, A.; Ruud, C. O. & McIlree, A. R.
Partner: UNT Libraries Government Documents Department

Partitioning behavior of alloying elements in PWA 1484

Description: Nominal composition of single-crystal PWA 1484 material is Ni-10.5 at.% Co, 6% Cr, 1.3% Mo, 2.0% W, 12.9% Al, 3.0% Ta, 0.04% Hf, and 1.0% Re. It was examined after standard heat treatment of 4 h at 1304 C, 4 h at 1079 C, and 24 h at 704 C. An atom probe field ion microscope was used. Co, Cr, Mo, W and Re partition to the {gamma} phase and Ni, Al, Ta, and Hf partition to the {gamma}` phase. Atom-by-atom data chains and statistical analysis did not show any evidence of Re clusters in the {gamma} matrix.
Date: August 1, 1996
Creator: Miller, M.K.; Lin, L.S.; Cetel, A.D.; Harada, H. & Murakami, H.
Partner: UNT Libraries Government Documents Department

Irradiation-induced microstructural changes in alloy X-750

Description: Alloy X-750 is a nickel base alloy that is often used in nuclear power systems for it`s excellent corrosion resistance and mechanical properties. The present study examines the microstructure and composition profiles in a heat of Alloy X-750 before and after neutron irradiation.
Date: April 1, 1997
Creator: Kenik, E.A.
Partner: UNT Libraries Government Documents Department

Nickel based superalloy with improved weldability and oxidation resistance. Fifth quarterly report for the period November 1999 - January 2000

Description: This program is part of the US Department of Energy (DOE) Energy Related Inventions Program (ERIP). The purpose of ERIP is to promote and facilitate the development of energy saving technologies that may not otherwise be developed solely by commercial enterprises. The program has been highly successful in achieving its mission. The aim of this project is to determine and provide technical and economic data to a commercial end user of the alloy so that a full-scale alloy qualification program can be defined and implemented. The object of this project is to define the compositional range for a new alloy that is suitable for evaluation and qualification by a commercial enterprise. Alloy properties that will need to be determined include weldability, oxidation resistance, creep strength, resistance to thermo-mechanical fatigue, microstructure stability, and cost. Test results will be used to finalize the compositional range of an alloy that will undergo a rigorous qualification process.
Date: February 29, 2000
Creator: Simkovich, George & Whitney, Eric
Partner: UNT Libraries Government Documents Department

Digital field ion microscopy

Description: Due to environmental concerns, there is a trend to avoid the use of chemicals needed to develop negatives and to process photographic paper, and to use digital technologies instead. Digital technology also offers the advantages that it is convenient, as it enables quick access to the end result, allows image storage and processing on computer, allows rapid hard copy output, and simplifies electronic publishing. Recently significant improvements have been made to the performance and cost of camera-sensors and printers. In this paper, field ion images recorded with two digital cameras of different resolution are compared to images recorded on standard 35 mm negative film. It should be noted that field ion images exhibit low light intensity and high contrast. Field ion images were recorded from a standard microchannel plate and a phosphor screen and had acceptance angles of {approximately} 60{degree}. Digital recordings were made with a Digital Vision Technologies (DVT) MICAM VHR1000 camera with a resolution of 752 x 582 pixels, and a Kodak DCS 460 digital camera with a resolution of 3,060 x 2,036 pixels. Film based recordings were made with Kodak T-MAX film rated at 400 ASA. The resolving power of T-MAX film, as specified by Kodak, is between 50 and 125 lines per mm, which corresponds to between 1,778 x 1,181 and 4,445 x 2,953 pixels, i.e. similar to that from the DCS 460 camera. The intensities of the images were sufficient to be recorded with standard fl:1.2 lenses with exposure times of less than 2 s. Many digital cameras were excluded from these experiments due to their lack of sensitivity or the inability to record a full frame image due to the fixed working distance defined by the vacuum system. The digital images were output on a Kodak Digital Science 8650 PS dye sublimation color printer ...
Date: January 1, 1998
Creator: Sijbrandij, S.J.; Russell, K.F.; Miller, M.K. & Thomson, R.C.
Partner: UNT Libraries Government Documents Department

Nickel Based Superalloy with Improved Weldability and Oxidation Resistance. Fourth quarterly report for the period July 1999 to October 1999

Description: The aim of this project is to determine and provide technical and economic data to a commercial end user of the alloy so that a full-scale alloy qualification program can be defined and implemented. The object of this project is to define the compositional range for a new alloy that is suitable for evaluation and qualification by a commercial enterprise. Alloy properties that will need to be determined include weldability, oxidation resistance, creep strength, resistance to thermo-mechanical fatigue, microstructure stability, and cost. Test results will be used to finalize the compositional range of an alloy that will undergo a rigorous qualification process.
Date: November 1, 1999
Creator: Simkovich, George & Whitney, Eric
Partner: UNT Libraries Government Documents Department

Gelcasting superalloy powders

Description: Gelcasting is a process for forming inorganic powders into complex shapes. It was originally developed for ceramic powders. A slurry of powder and a monomer solution is poured in to mold and polymerized in-situ to form gelled parts. Typically, only 2-4 wt % Polymer is used. The process has both aqueous and nonaqueous versions. Gelcasting is a generic process and has been used to produce ceramic parts from over a dozen different ceramic compositions ranging from alumina-based refractories to high-performance silicon nitride. Recently, gelcasting has been applied to forming superalloy powders into complex shapes. This application has posed several challenges not previously encountered in ceramics. In particular, problems were caused by the larger particle size and the higher density of the particles. Additional problems were encountered with binder removal. How these problems were overcome will be described.
Date: December 31, 1995
Creator: Janney, M.A.
Partner: UNT Libraries Government Documents Department

Creep of nickel-base alloys in high temperature water

Description: Creep tests were performed to compare the creep behavior of commercial nickel-base alloys as a function of stress, temperature, and the environment. The results support earlier work that showed that low carbon alloys are more susceptible to creep and intergranular cracking than are high carbon alloys. Results also show a smaller influence of a water environment on the creep rate of commercial, creep-resistant alloys compared to high purity alloys.
Date: August 1, 1999
Creator: Fish, J.S.; Attanasio, S.A.; Krasodomski, H.T.; Wilkening, W.W.; Was, G.S.; Cookson, J. et al.
Partner: UNT Libraries Government Documents Department

Experimental Studies on the Effect of Coherency Strains on Coarsening Kinetics: Current Status and Future Outlook

Description: The effect of coherency strains on the coarsening rate constant in Ostwald ripening is an area that is not well understood. We briefly review the extant experimental data on the effect of coherency strains on coarsening rates and explain the need to account for variations in coarsening rates due to composition and diffusivity effects before drawing any conclusions on the dependence of coarsening rates on the misfit parameter. Using the preexisting theories for coarsening rates in multi-component systems, we suggest a simple method to account for the composition dependence of coarsening rates arising from factors unrelated to coherency strain effects. We then present some of the results from our on-going work in the Ni-Al-Si system and explain the relevance of this study to our understanding of coarsening in internally-stressed systems. We conclude the presentation with our views on the direction of future research in this aspect of coarsening.
Date: March 1, 1994
Creator: Muralidharan, G.; Epperson, J. E. & Chen, H.
Partner: UNT Libraries Government Documents Department

Investigations of the reduction of NiAl{sub 2}O{sub 4}. 2: X-ray diffraction studies

Description: The volume shrinkage that accompanies the reduction of NiAl{sub 2}O{sub 4} to a metal-ceramic composite of nickel and alumina leads to residual stress buildup. The authors have attempted to utilize these stresses to temper a ceramic component by placing it under compression. To prove the concept, they produced model specimens which they investigated using X-ray diffraction. Employing the conventional d vs. sin{sup 2} {Psi} method to map surface stresses, the results obtained from these measurements are presented together with finite element calculation predictions used to interpret experimental stress data.
Date: September 1, 1998
Creator: Clausen, B.; Rangaswamy, P.; Bourke, M.A.M.; Uestuendag, E.; Sass, S.L. & Barbieri, T.J.
Partner: UNT Libraries Government Documents Department

A Parametric Analysis of Solidification in Y(Fe,Ni,Cr)-Nb-C Alloys

Description: A parametric analysis is presented which summarizes the amount of total ({gamma}/NbC + {gamma}/Laves) and individual {gamma}/NbC and {gamma}/Laves constituents which form during solidification of {gamma}{sub (Fe,Ni,Cr)} alloys with variations in nominal Nb and C contents. Calculated results are presented for Fe base alloys and Ni base alloys. The results provide a quantitative rationale for understanding the relation between alloy composition and solidification microstructures and should provide useful insight into commercial alloys of similar composition.
Date: February 22, 1999
Creator: DuPont, J.N. & Robino, C.V.
Partner: UNT Libraries Government Documents Department

Effects of ion implantation and temperature on radiation-induced segregation in Ni-9Al alloys

Description: Effects of Ne and Sc implantation on radiation-induced segregation (RIS) in Ni-9at.%Al were studied in-situ using the high-voltage electron microscope/Tandem accelerator at ANL. A highly-focused 900- keV electron beam generated radial defect fluxes which, in turn, induced transport of Al atoms toward the center of the electron- irradiated area via the inverse Kirkendall effect. Radial segregation rate of Al atoms was monitored by measuring the diameter of the {gamma}{prime}-Ni{sub 3}Al zone which formed in the Al-enriched area during irradiation. Ne and Sc implantation effects on RIS were investigated at 550 C; Ne effects were also examined at 625 C to determine effect of temperature on ability of Ne to act as defect trapping sites, causing RIS suppression. It was found that the RIS suppression effect of Ne increased with irradiation temperature and that Sc had a small RIS suppression effect which increased with Sc implantation dose. Ne bubbles which formed during implantation are believed to be responsible for its strong suppression effect. 6 figs, 12 refs
Date: December 1, 1996
Creator: Giacobbe, M.J.; Lam, N.Q.; Okamoto, P.R.; Zaluzec, N.J. & Stubbins, J.F.
Partner: UNT Libraries Government Documents Department

Weldability and microstructure development in nickel-base superalloys

Description: The integrity of nickel-base superalloy single-crystal welds depends on the weld cracking tendency, weld metal dendrite selection process, stray crystal formation, and macro- and microstructure development. These phenomena have been investigated in commercial nickel-base superalloy single crystal welds. During electron beam and laser beam welding, transverse and longitudinal weld cracking occurred. However, the weld cracking tendency was reduced with preheating. Most of the dendritic growth pattern development in these welds can be explained by a geometric model. However, the welds also contained misoriented stray crystals, which were frequently associated with weld cracks. The formation of stray crystals was related to thermal and constitutional supercooling effects. Fine-scale elemental partitioning between {gamma} and {gamma}{prime} phase was measured with atom-probe field-ion microscopy. Marked differences in partitioning characteristics in two welds were observed and are related to differences in cooling rates. In this paper, the modeling tools available to describe the above are reviewed.
Date: November 1, 1997
Creator: David, S.A.; Babu, S.S. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department

Optical and analytical electron microscopy of ductility-dip cracking in Ni-base filler metal 52 -- Initial studies

Description: Microcharacterization studies were performed on weld-metal microstructures of a Ni-base filler metal. Specimens were taken from the fusion zone and the weld-metal heat-affected zone of transverse- and spot-Varestraint welds. The filler metal was first deposited onto a steel substrate by hot-wire, gas tungsten arc welding before specimen removal. Optical microscopy indicates the crack morphology is intergranular and is along high-angle, migrated grain boundaries. At low magnifications, scanning electron microscopy reveals a relatively smooth fracture surface. However, at higher magnifications the grain faces exhibit microductility. Analytical electron microscopy reveals high-angle, migrated grain boundaries decorated with MC (Ti, Cr) and M{sub 23}C{sub 6} (Cr, Ni, Fe) precipitates ranging from 10 to 200 n. Auger electron spectroscopy of pre-strained Gleeble specimens fractured in situ revealed internal ductility-dip cracks decorated with magnesium aluminate (MgAl{sub 2}O{sub 4}) spinel particles (1,000 nm).
Date: January 1, 1998
Creator: Cola, M.J. & Teter, D.F.
Partner: UNT Libraries Government Documents Department

Atom probe field-ion microscopy investigation of nickel base superalloy welds

Description: Microstructure development and elemental partitioning between {gamma} and {gamma}{prime} were measured in PWA-1480 electron beam welds and CMSX-4 pulsed-laser welds. In PWA-1480 EB welds, eutectic {gamma}{prime} phases were observed along the dendritic boundaries. The elemental partitioning between {gamma} and {gamma}{prime} was found to be similar to that in PWA-1480 base metal. In CMSX-4 pulsed laser welds, negligible eutectic {gamma}{prime} was observed. In addition, fine and irregularly shaped {gamma}{prime} precipitates were observed. The elemental partitioning between {gamma} and {gamma}{prime} was found to be different from that measured in the base metal. Large concentration gradients were observed in the {gamma} phase. The {gamma}{prime} precipitation kinetics in CM247DS alloy was measured using dilatometry and showed differences with different cooling rates. The microstructural investigations showed that at large undercoolings the number density of {gamma}{prime} precipitates increased and led to a finer size. This supports the microstructure development observations in PWA-1480 and CMSX-4 welds. Thermodynamic and kinetic calculations for the Ni-Al-Cr alloy system showed that as the cooling rate increases, the {gamma}{prime} growth leads to large concentration gradients in the {gamma} phase. The calculations agree with the atom probe results from PWA-1480 and CMSX-4 welds.
Date: November 1, 1998
Creator: Babu, S.S.; David, S.A.; Vitek, J.M. & Miller, M.K.
Partner: UNT Libraries Government Documents Department

Neutron scattering characterization of microstructure in uranium silicides, ceramic composites and Ni-based alloys

Description: Neutron scattering has proven to be a valuable tool for studying the microstructural properties of technologically important materials. The exceptionally high penetration power of neutrons enables the investigation of bulk materials, while unusual scattering contrasts observed in many materials provide unique access to important properties. Macroscopic performance of components under extreme conditions, which ultimately determines their viability for special applications, is often closely related to microstructural properties such as particle size, residual stress and phase stability. Neutron scattering experiments performed with samples exposed to realistic environmental conditions provide direct correlation between microscopic and macroscopic properties. Neutron irradiation of uranium silicide (a prospective reactor fuel), is used here as a prototypical example of in situ residual stress generation and evolution, accompanied by direct amorphization. Neutron diffraction studies at IPNS identified structural instabilities which contributed to material failure. Highly accurate measurements of residual strains in ceramic composites are used to validate computer models for stress variation with temperature and the effects of interfacial fiber coatings on residual stress. Coarsening and lattice mismatch of {gamma}{prime}-type Ni{sub 3}(Al,Si) particles in Ni-based alloys, which strongly influence coherency strains in these materials, are also measured directly using neutron scattering.
Date: October 1, 1997
Creator: Richardson, J.W. Jr.
Partner: UNT Libraries Government Documents Department

Processing, properties, and applications of Ni{sub 3}Al-based alloys

Description: The Ni{sub 3}Al-based alloys represent a quantum jump in advanced alloys for structural applications at elevated temperatures. These alloys offer benefits of oxidation, carburization, and chlorination resistance, and significantly higher strength than many commercially used alloys. The commercial applications of the Ni{sub 3}Al-based alloys have begun to occur because of their comprehensive development This paper is to provide a review of. (1) alloy development, (2) melting, casting, and processing of alloys, (3) property data, (4) welding process and weldment properties, and (5) case histories of current applications. It is concluded that the cast alloy IC-221M is on its way to commercialization. 22 refs., 8 figs., 2 tabs.
Date: June 1, 1997
Creator: Sikka, V.K.; Santella, M.L. & Liu, C.T.
Partner: UNT Libraries Government Documents Department

A comparison of internal hydrogen embrittlement and hydrogen environment embrittlement of X-750

Description: Hydrogen has been shown to degrade the mechanical properties of nickel-base alloys. This degradation occurs whether the material is in a hydrogen producing environment or if the material has dissolved hydrogen in the metal due to prior exposure to hydrogen. Materials behave differently under these two conditions. Therefore, the degradation due to hydrogen has been split into two categories, internal hydrogen embrittlement (IHE) and hydrogen environment embrittlement (HEE). IHE may be defined as the embrittlement of a material that has been charged with hydrogen prior to testing or service while HEE may be defined by the embrittlement of a material in a hydrogen environment where the hydrogen may come from gaseous hydrogen or generated from a corrosion reaction. This work will compare IHE and HEE of fracture mechanics specimens. Different fugacities of hydrogen for HEE and hydrogen concentrations for IHE were examined for Alloy X-750, a nickel-base super alloy. The test results were analyzed and the role of hydrogen in IHE and HEE was evaluated. A model based on a critical grain boundary hydrogen concentration will be proposed to describe the behavior in both HEE and IHE conditions.
Date: December 1, 1999
Creator: Symons, D.M.
Partner: UNT Libraries Government Documents Department

Modeling solute redistribution and microstructural development in fusion welds of multi-component alloys

Description: Solute redistribution and microstructural evolution have been modeled for gas tungsten arc fusion welds in experimental Ni base superalloys. The multi-component alloys were modeled as a pseudo-ternary {gamma}-Nb-C system. The variation in fraction liquid and liquid composition during the primary L {r{underscore}arrow} {gamma} and eutectic type L {r{underscore}arrow} ({gamma} + NbC) stages of solidification were calculated for conditions of negligible Nb diffusion and infinitely rapid C diffusion in the solid phase. Input parameters were estimated by using the Thermo-Calc NiFe Alloy data base and compared to experimentally determined solidification parameters. The solidification model results provide useful information for qualitatively interpreting the influence of alloy composition on weld microstructure. The quantitative comparisons indicate that, for the alloy system evaluated, the thermodynamic database provides sufficiently accurate values for the distribution coefficients of Nb and C. The calculated position of the {gamma}-NbC two-fold saturation line produces inaccurate results when used as inputs for the model, indicating further refinement to the database is needed for quantitative estimates.
Date: December 15, 1999
Creator: Dupont, J.N.; Robino, C.V. & Newbury, B.D.
Partner: UNT Libraries Government Documents Department

Phase stability and mechanical properties of c-22 alloy aged in the temperature range 590 to 760 degree c for 16,000 hours

Description: The phase stability of C-22 alloy (UNS #N06022) was studied by aging samples at 593, 649, 704 and 760°C for 2000 h (2.7 mo) and 16,000 h (1.8 yr). The tensile properties and the Charpy impact toughness of these samples were measured in the mill annealed condition as well as after aging. The microstructures of samples aged 16,000 hours were examined using scanning and transmission electron microscopy (SEM and TEM). Preliminary TEM results suggest that m phase forms at all temperatures investigated. Discrete carbide particles in addition to a film with very uniform thickness which appears to be m phase formed on grain boundaries in the sample aged at 593°C. The ordered Ni<sub>2</sub>(Cr, Mo) phase was also seen in this sample. At the higher aging temperatures, mainly m phase forms covering all the grain boundaries and also distributed throughout the bulk. Although strength increased somewhat with aging, the ductility decreased due to the formation of these grain boundary precipitates and brittle intermetallics.
Date: December 1998
Creator: Edgecumbe Summers, T. S.; Kumar, M.; Mathews, S. J.; Rebak, R. B. & Wall, M. A.
Partner: UNT Libraries Government Documents Department

Some effects of metallic substrate composition on degradation of thermal barrier coatings

Description: Comparisons have been made in laboratory isothermal and cyclic oxidation tests of the degradation of oxide scales grown on single crystal superalloy substrates and bond coating alloys intended for use in thermal barrier coatings systems. The influence of desulfurization of the superalloy and bond coating, of reactive element addition to the bond coating alloy, and of oxidation temperature on the spallation behavior of the alumina scales formed was assessed from oxidation kinetics and from SEM observations of the microstructure and composition of the oxide scales. Desulfurization of nickel-base superalloy (in the absence of a Y addition) resulted in an increase in the lifetime of a state-of-the-art thermal barrier coating applied to it compared to a Y-free, non-desulfurized version of the alloy. The lifetime of the same ceramic coating applied without a bond coating to a non-desulfurized model alloy that formed an ideal alumina scale was also found to be at least four times longer than on the Y-doped superalloy plus state-of-the-art bond coating combination. Some explanations are offered of the factors controlling the degradation of such coatings.
Date: December 1997
Creator: Wright, I. G.; Pint, B. A.; Lee, W. Y.; Alexander, K. B. & Pruessner, K.
Partner: UNT Libraries Government Documents Department

Electrodeposited tungsten-nickel-boron: A replacement for hexavalent chromium

Description: Chromium, deposited from acidic solutions of its hexavalent ion, has been the rule for wear resistant, corrosion resistant coatings for many years. Although chromium coatings are durable, the plating process generates air emissions, effluent rinse waters, and process solutions that are toxic, suspected carcinogens, and a risk to human health and the environment. Tungsten-nickel-boron (W-Ni-B) alloy deposition is a potential substitute for hexavalent chrome. It has excellent wear, corrosion, and mechanical properties and also may be less of an environmental risk. This study examines the electroplating process and deposit properties of W-Ni-B and compares them with those of hexavalent chrome.
Date: April 1, 1995
Creator: Steffani, C. & Meltzer, M.
Partner: UNT Libraries Government Documents Department