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Atom Probe Field Ion Microscopy of Zr-Doped Polysynthetically Twinned Titanium Aluminide

Description: Interracial segregation and partitioning in a polysynthetically twinned Ti-48.4 at.% Al-0.6% Zr alloy were investigated by atom probe field ion microscopy and atom probe tomography. The compositions of the {gamma} and {alpha}{sub 2} phases were determined to be Ti-47.5% Al-O.71% Zr-0.06% O and Ti-31.6% Al-0.68% Zr-2.4% O, respectively. These results indicate a high concentration of zirconium in both matrix phases, confirming a strength increase through solid-solution strengthening, but no significant zirconium partitioning to either phase. Although zirconium additions produced a refined lamellar microstructure in this material, compositional analysis of {gamma}/{gamma} and {gamma}/{alpha}{sub 2} interfaces showed no evidence of significant zirconium segregation. This suggests that zirconium additions may produce a refined lamellar microstructure, but may not be effective at providing resistance to growth and coarsening.
Date: February 28, 1999
Creator: Inui, H.; Larson, D.J.; Miller, M.K. & Yamaguchi, M.
Partner: UNT Libraries Government Documents Department

High temperature deformation in 2036 Al and 0.2 wt % Zr-2036 A1

Description: The microstructure and high-temperature deformation of 2036 Al and a 0.2 wt % Zr modified 2036 Al were characterized. A particle-simulated- nucleation process was applied to refine grain structure in both alloys. Thermomechanically processed materials were tested from 450 to 500 C and strain rates from 2{times}10{sup {minus}1} to 2{times}10{sup {minus}4}s{sup {minus}1}. Strain rate sensitivity exponent, activation energy, and total elongation were measured, and the deformation mechanism was proposed. Effect of Zr on microstructure and deformation of 2036 Al at elevated temperatures was discussed.
Date: November 1, 1995
Creator: Huang, J.S.; Schwartz, A.J. & Nieh, T.G.
Partner: UNT Libraries Government Documents Department

Stress determination in thermally grown alumina scales using ruby luminescence

Description: By exploiting the strain dependence of the ruby luminescence line, we have measured the strain in alumina scales thermally grown on Fe-Cr- Al alloys. Results are compared and found to be reasonably consistent with strains determined using x rays. Oxidation studies were carried out on alloys Fe - 5Cr - 28Al and Fe - 18Cr - 10Al (at.%). Significantly different levels of strain buildup were observed in scales on these alloys. Results on similar alloys containing a ``reactive element`` (Zr or Hf) in dilute quantity are also presented. Scales on alloys containing a reactive element (RE) can support significantly higher strains than scales on RE-free alloys. With the luminescence technique, strain relief associated with spallation thresholds is readily observed.
Date: June 1, 1996
Creator: Renusch, D.; Veal, B. W.; Koshelev, I.; Natesan, K.; Grimsditch & Hou, P. Y.
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

Investigation of moisture-induced embrittlement of iron aluminides. Final report

Description: Iron-aluminum alloys with 28 at.% Al and 5 at.% Cr were shown to be susceptible to hydrogen embrittlement by exposure to both gaseous hydrogen and water vapor. This study examined the effect of the addition of zirconium and carbon on the moisture-induced hydrogen embrittlement of an Fe{sub 3}Al,Cr alloy through the evaluation of tensile properties and fatigue crack growth resistance in hydrogen gas and moisture-bearing air. Susceptibility to embrittlement was found to vary with the zirconium content while the carbon addition was found to only affect the fracture toughness. Inherent fatigue crack growth resistance and fracture toughness, as measured in an inert environment, was found to increase with the addition of 0.5 at.% Zr. The combined addition of 0.5 at.% Zr and carbon only increased the fracture toughness. The addition of 1 at.% Zr and carbon was found to have no effect on the crack growth rate when compared to the base alloy. Susceptibility to embrittlement in moisture-bearing environments was found to decrease with the addition of 0.5 at.% Zr. In gaseous hydrogen, the threshold value of the Zr-containing alloys was found to increase above that found in the inert environment while the crack growth resistance was much lower. By varying the frequency of fatigue loading, it was shown that the corrosion fatigue component of the fatigue crack growth rate in an embrittling environment displays a frequency dependence. Hydrogen transport in iron aluminides was shown to occur primarily by a dislocation-assisted transport mechanism. This mechanism, in conjunction with fractography, indicates that the zirconium-containing precipitates act as traps for the hydrogen that is carried along by the dislocations through the lattice.
Date: June 5, 1997
Creator: Alven, D. A. & Stoloff, N.S .
Partner: UNT Libraries Government Documents Department

The influence of composition on environmental embrittlement of iron aluminides

Description: The effects of water vapor in air and hydrogen gas on the tensile and fatigue crack growth behavior of Fe{sub 3}Al alloys have been studied at room temperature. Fe-28a% Al-5a% Cr alloys to which either Zr alone or Zr and C have been added and tested in controlled humidity air environments as well as in 1.3 atm hydrogen or oxygen gas and in vacuum. As with other Fe{sub 3}Al alloys, oxygen produces the lowest crack growth rates as well as the highest critical stress intensities and tensile ductility in each of the alloys tested. However, while Zr lowers crack growth rates in the Paris regime, there is no apparent beneficial effect on crack growth thresholds. Hydrogen gas also produces unusual results. While crack growth rates are very high in hydrogen in the Paris regime for all alloys, hydrogen only lowers the crack growth threshold relative to air in ternary Fe-28Al-5Cr; it does not lower the threshold in the Zr-containing alloys. It was found that decreased test frequency leads to increased crack growth rates in a Zr-containing alloy which points to a moisture-induced embrittlement mechanism responsible for the higher crack growth rates in air. Fracture path tends to be insensitive to environment for each alloy.
Date: July 1, 1996
Creator: Alven, D. A. & Stoloff, N. S.
Partner: UNT Libraries Government Documents Department

Cr{sub 2}Nb-based alloy development

Description: This paper summarizes recent progress in developing Cr{sub 2}Nb/Cr(Nb) alloys for structural use in advanced fossil energy conversion systems. Alloy additions were added to control the microstructure and mechanical properties. Two beneficial elements have been identified among all alloying additions added to the alloys. One element is effective in refining the coarse eutectic structure and thus substantially improves the compressive strength and ductility of the alloys. The other element enhances oxidation resistance without sacrificing the ductility. The tensile properties are sensitive to cast defects, which can not be effectively reduced by HIPping at 1450-1580{degrees}C and/or directionally solidifying via a floating zone remelting method.
Date: May 1, 1996
Creator: Liu, C.T.; Horton, J.A. & Carmichael, C.A.
Partner: UNT Libraries Government Documents Department

Evaluation of the intrinsic and extrinsic fracture behavior of iron aluminides

Description: Iron aluminides have excellent corrosion resistance in high-temperature oxidizing-sulfidizing environments; however, there are problems at room and medium temperatures with hydrogen embrittlement as related to exposure to moisture. In this research, a coordinated computational modeling/experimental study of mechanisms related to environmental-assisted fracture behavior of selected iron aluminides has been undertaken. The modeling and the experimental work connect at the level of coordinated understanding of the mechanisms for hydrogen penetration and for loss of strength and susceptibility to fracture. The focus of the modeling component has been on the challenging question of accurately predicting the iron vacancy formation energy in Fe{sub 3}Al and the subsequent tendency, if present, for vacancy clustering. The authors have successfully performed, on an ab initio basis, the first calculation of the vacancy formation energy in Fe{sub 3}Al. These calculations include lattice relaxation effects which are quite large for one of the two types of iron sites. This has significant implications for vacancy clustering effects with consequences for hydrogen diffusion. Indeed, the ab-initio-based estimate of the divacancy binding energy indicates a likely tendency toward such clustering for iron vacancies on the sites with large lattice relaxation. The experimental work has focused on the relationship of the choice and concentration of additives to the improvement of resistance to hydrogen embrittlement and hence to the fracture behavior.
Date: July 27, 1998
Creator: Cooper, B.R. & Kang, B.S.
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

The effects of zirconium and carbon on the hot cracking resistance of iron aluminides. Topical report

Description: Iron aluminides have been of interest for about 60 years because of their good high temperature strengths (below 600{degrees}C) and excellent oxidation and sulfidation resistance, as well as their relatively low cost and conservation of strategic elements. These advantageous properties have driven the development of iron aluminides as potential structural materials. However, the industrial application of iron aluminides has been inhibited because of a sharp reduction in strength at temperatures higher than 600{degrees}C and low ductility at ambient temperatures due to hydrogen embrittlement. Oak Ridge National Laboratory has shown in recent years that room temperature properties of alloys containing 28% Al (all compositions are in atomic percent unless otherwise noted) can be improved through thermomechanical processing and alloying. Iron aluminides must have good weldability if they are to be used as structural materials. A coarse fusion zone microstructure is formed when iron aluminides are welded, increasing their susceptibility to cold cracking in water vapor. A recent study at Colorado School of Mines has shown that refining the fusion zone microstructure by weld pool oscillation effectively reduces cold cracking. Weld pool inoculation has been shown to refine fusion zone microstructures, but coarse carbide distribution caused this approach to reducing cold cracking to be ineffective.
Date: February 1, 1998
Creator: Mulac, B.L.; Edwards, G.R. & David, S.A.
Partner: UNT Libraries Government Documents Department

The Interaction of Dissolved H with Internally Oxidized Pd-Rh Alloys

Description: Binary Pd-M alloys containing small amounts of readily oxidizable solute metals such as M equals Al, Mg, or Zr, can be internally oxidized to form essentially pure Pd matrices containing a second phase of nano-sized oxide precipitates. During internal oxidation Pd atoms are transported to the surface forming Pd nodules while vacancies are transported from the surface to the metal/oxide interface relieving the compressive stress which develops within the alloy due to the expanding metal oxide precipitates. The Pd alloys that have been studied contain that form very stable oxides.
Date: April 20, 2001
Creator: Shanahan, K.L.
Partner: UNT Libraries Government Documents Department

Thermomechanical processing of a two-phase Al-Cu-Li-Zr alloy

Description: The effect of large second-phase particles on the workability, mechanical properties, and response to thermochemical processing of an Al-2.49Cu-2.37Li-0.13Zr alloy was investigated. The solution-treated alloy was compared with a dispersoid-containing alloy fabricated by aging the base alloy at an intermediate temperature to bring out second-phase particles. Extensive deformation and short heat treatments that cause some of the solute to be incorporated into dispersoid particles were both found to be beneficial to the mechanical properties of the alloy. In specimens which failed intergranularly, the presence of dispersoid particles did not significantly affect the fracture properties.
Date: June 1, 1985
Creator: Glazer, J. & Morris, J.W. Jr.
Partner: UNT Libraries Government Documents Department

Alloy development and processing of FeAl: An overview

Description: In the last few years, considerable progress has been made in developing B2-phase FeAl alloys with improved weldability, room-temperature ductility, and high-temperature strength. Controlling the processing-induced microstructure is also important, particularly for minimizing trade-offs in various properties. FeAl alloys have outstanding resistance to high-temperature oxidation, sulfidation, and corrosion in various kinds of molten salts due to formation of protective Al{sub 2}O{sub 3} scales. Recent work shows that FeAl alloys are carburization-resistant as well. Alloys with 36 to 40 at. % Al have the best combination of corrosion resistance and mechanical properties. Minor alloying additions of Mo, Zr, and C, together with microalloying additions of B, produce the best combination of weldability and mechanical behavior. Cast FeAl alloys, with 200 to 400 {mu}m grain size and finely dispersed ZrC, have 2 to 5% tensile ductility in air at room-temperature, and a yield strength > 400 MPa up to about 700 to 750{degrees}C. Extruded ingot metallurgy (I/M) and powder metallurgy (P/M) materials with refined grain sizes ranging from 2 to 50 {mu}m, can have 10 to 15% ductility in air and be much stronger, and can even be quite tough, with Charpy impact energies ranging from 25 to 105 J at room-temperature. This paper highlights progress made in refining the alloy composition and exploring processing effects on FeAl for monolithic applications. It also includes recent progress on developing FeAl weld-overlay technology, and new results on welding of FeAl alloys. It summarizes some of the current industrial testing and interest for applications.
Date: March 1, 1997
Creator: Maziasz, P.J.; Goodwin, G.M.; Alexander, D.J. & Viswanathan, S.
Partner: UNT Libraries Government Documents Department

A review of compatibility of IFR fuel and austenitic stainless steel

Description: Interdiffusion experiments have been conducted to investigate the compatibility of various austenitic stainless steels with U-Pu-Zr alloys, which are alloys to be employed as fuel for the Integral Fast Reactor being developed by Argonne National Laboratory. These tests have also studied the compatibility of austenitic stainless steels with fission products, like the minor actinides (Np and Am) and lanthanides (Ce and Nd), that are generated during the fission process in an IFR. This paper compares the results of these investigations in the context of fuel-cladding compatibility in IFR fuel elements, specifically focusing on the relative Interdiffusion behavior of the components and the types of phases that develop based on binary phase diagrams. Results of Interdiffusion tests are assessed in the light of observations derived from post-test examinations of actual irradiated fuel elements.
Date: November 1, 1996
Creator: Keiser, D.D. Jr.
Partner: UNT Libraries Government Documents Department

Effect of heat treatment at 1,150 C on creep rupture properties of a Fe{sub 3}Al-based alloy

Description: The effects of heat treatment at 1,150 C on the creep-rupture properties of a Fe{sub 3}Al-based alloy were studied. Tests were conducted in air using various test temperatures and stresses. By plotting the data to a power-law equation, the activation energy for creep was determined to be approximately 150 kcal/mole and the creep exponent to be about 8. Optical metallography and scanning electron microscopy of ruptured specimens indicated that failure was in a ductile manner by microvoid coalescence at grain boundaries and triple points. Analytical electron microscopy was used to study characteristics of the microstructure and to identify Zr-rich precipitates that formed during heat treatment or creep testing. These precipitates were found to provide strengthening by pinning dislocations and grain boundaries.
Date: December 31, 1994
Creator: McKamey, C.G.; Maziasz, P.J. & Marrero-Santos, Y.
Partner: UNT Libraries Government Documents Department

Ductile nickel-silicon alloy

Description: An improvement over prior compositions wherein the ductility of Ni-Si alloys are improved with minor alloying additions of hafnium or zirconium.
Date: August 6, 1990
Creator: Oliver, W.C.
Partner: UNT Libraries Government Documents Department

Long-range-ordered alloys modified by Group IV-B metals

Description: Ductile long range ordered alloys having high critical ordering temperatures exist in the (V,M)(Fe,Ni,Co)/sub 3/ system having the composition comprising by weight 20.6 to 22.6% V, 14 to 50% Fe, 0 to 64% Co, and 0 to 40% Ni, and 0.4 to 1.4% M, where M is a metal selected from the group consisting of Ti, Zr, Hf, and their mixtures. These modified alloys have an electron density no greater than 8.00 and exhibit marked increases at elevated temperature in ductility and other mechanical properties over previously known ordered alloys.
Date: May 22, 1981
Creator: Liu, C.T.; Inouye, H. & Schaffhauser, A.C.
Partner: UNT Libraries Government Documents Department

Work hardening behavior in aluminum alloy 2090

Description: An investigation into the work hardening behavior of an aluminum alloy 2090-T81 Al-3.05Cu-2.16Li-0.12Zr at various test temperatures, heat treatment conditions and microstructures was conducted. One microstructure consisted of unrecrystallized, highly textured grains, and the other microstructure was composed of recrystallized grains. Microstructural effects on work hardening were divided into two levels of contribution: the grain structure level, which consisted of the grain size and shape, subgrains and texture, and the microconsistent level, which included the precipitates and solutes. Two heat treatments were studied: the as-received, peak-aged condition, and the solution heat treated condition where the as-received plate was resolutionized. Observations of the deformed surface of both as-received grain structures at various prestrains indicated that there was no correlation between an increase in slip homogeneity and an increase in work hardening. The increase in out-of-plane grain rotation at lower temperatures was not primarily responsible for the increase in work hardening. In addition, the fully plastic deformation microstructure for the unrecrystallized microstructure appeared very inhomogeneous as the grains deformed in bands; there were also bands of grains that had very little to no deformation. From the work hardening plots it was found that an unrecrystallized, (110)<112> textured grain structure with a homogeneous distribution of subgrains produced the highest rate of work hardening between 300 K and 77 K. When the microconstituents are added to both grain structures, both the work hardening rate in the elastic-plastic and fully plastic regimes and the level of work hardening at which the elastic-plastic to fully plastic transition occurred were affected.
Date: December 1, 1993
Creator: Tseng, C.
Partner: UNT Libraries Government Documents Department

Oxidation/sulfidation behavior of Fe-Cr alloys: A reactive-element effect

Description: Corrosion resistance of a number of structural alloys in high-temperature environments is achieved by the formation of a continuous chromium oxide scale. Research on high-temperature corrosion of structural alloys has been in progress to reduce the rate of oxidation, improve the adhesion of oxide scale to the substrate alloy, and to stabilize the oxide scale against other corrosive agents such as sulfur, chlorine, alkalies, and ash/sorbent deposits. Extensive research is being conducted at Argonne National Laboratory to (1) evaluate mechanisms of oxidation, sulfidation, and break-away corrosion of chromia- and alumina-forming alloys exposed to mixed-gas atmospheres that span a wide range of oxygen, sulfur, and chlorine activities typical of combustion and gasification systems; (2) develop an understanding of the role of several microalloy constituents (e.g., Zr, Nb, Y, Ce, V) in oxidation/sulfidation processes and scale breakdown; (3) characterize the physical, chemical and mechanical properties of surface scales that are resistant to sulfidation attack; and (4) evaluate the role of deposits, such as alkali sulfates, alkali chlorides, ash, and sulfur sorbents, in the corrosion behavior or metallic alloys, selected coatings, and ceramic materials.
Date: April 1, 1992
Creator: Natesan, K. & Park, J. H.
Partner: UNT Libraries Government Documents Department

The effect of reactive elements on the segregation behavior and microstructure of {alpha}-Al{sub 2}O{sub 3} scales on {beta}-NiAl

Description: In order to improve oxidation resistance, small amounts of oxygen- active or ``reactive`` elements (RE) such as Y, Zr, Hf, Ce are added to chromia- and alumina-forming high-temperature alloys. As an alternative to a system where the RE-ion supply is self-limiting (Y-implant), it was desired to study effect of RE source-removal on microstructure and grain boundary segregation levels. {beta}-NiAl doped with 0.23 wt% Zr was oxidized in oxygen at 1500 C for 50 h. Upon cooling, the scale spalled into pieces; these spalled {alpha}-Al{sub 2}O{sub 3} scales were then annealed in air at 1500 C for 1 and 50 h. Specimens were fabricated parallel to metal/scale interface, and grain boundary chemistries were determined using X-ray energy dispersive spectrometry. Results show that no qualitative change in microstructural scale or zirconia particle size/density occurs after annealing, which is consistent with the model in which the gas- interface microstructure development depends on a continuous supply of zirconia diffusing from the metal interface towards the gas interface.
Date: June 1, 1994
Creator: Alexander, K. B. & Pint, B. A.
Partner: UNT Libraries Government Documents Department

Effect of heat treatment at 1150 C on creep-rupture properties of alloy FA-180

Description: The alloy FA-180, with a composition of Fe-28Al-5Cr-0.5Nb-0.8Mo-0.025Zr-0.05C-0.005B (at.%), is of interest because of its improved creep-rupture resistance when compared to alloy FA-129 (Fe-28Al-5Cr-0.5Nb-0.2C). At a temperature of 593 C and under a stress of 207 MPa, the creep-rupture life of FA-129 heat treated for 1 h at 750 C is about 20 h while the FA-180 alloy lasts approximately 100 h. Heat treatment at 1,150 C has been shown to further improve the creep life of FA-180 and creep-rupture lives of approximately 2,000 h have been attained. This strengthening was attributed to the presence of fine matrix and grain boundary Zr-rich MC precipitates that were produced by the heat treatment. The current study continues the investigation of the effect of heat treatment at 1,150 C on the improvement of creep-rupture life in alloy FA-180. As part of the effort to understand the strengthening mechanisms involved with heat treatment at 1,150 C, transmission electron microscopy was used to correlate the microstructure with the improved creep resistance. Results indicate that heat treatment at 1,150 C for 1 h, followed by rapid quenching in water or mineral oil, produces even further improvements in the creep-rupture life of this alloy. A specimen being tested at 593 C and 207 MPa was stopped after over 6000 h of life, while another specimen lasted over 1,600 h at 650 C and 241 MPa. The microstructure of the oil-quenched specimen contained many dislocation loops which were not present in the air-cooled specimens. These loops pinned dislocations during creep testing at temperatures of 593--700 C, resulting in stabilized deformation microstructure and increased creep-rupture strength.
Date: August 1, 1996
Creator: McKamey, C.G. & Maziasz, P.J.
Partner: UNT Libraries Government Documents Department

High-temperature corrosion behavior of iron-aluminide alloys and coatings

Description: An Fe-28 at.% Al-2% Cr alloy doped with Y{sub 2}O{sub 3} showed improved scale adhesion relative to a dispersion-free form of the same composition. However, doping with CeO{sub 2} or La{sub 2}O{sub 3} was detrimental to oxidation behavior. A study of weld-overlay iron-aluminide coatings showed that, those with sufficiently high aluminum concentrations had sulfidation resistance in H{sub 2}S-H{sub 2}-H{sub 2}O-Ar at 800 C equivalent to the most resistant bulk iron aluminides. These corrosion-resistant coatings have the potential to be effective barriers in high-temperature sulfidizing environments provided the appropriate combinations of filler metal, process parameters, and substrate are used to produce adequate aluminum concentrations and minimal chromium contents. Exposures in an oxidizing/sulfidizing environment containing varying amounts of HCI at 450 and 550 C showed that Fe{sub 3}Al alloys had good corrosion resistance.
Date: July 1995
Creator: Tortorelli, P. F.; DeVan, J. H.; Pint, B. A.; Wright, I. G. & Saunders, S. R. J.
Partner: UNT Libraries Government Documents Department