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Diffusion of Uranium with Various Transitional Metals; DIFFUSION DE L'URANIUM AVEC QUELQUES METAUX DE TRANSITION

Description: The diffusion process in uranium and its alloys was studied from 550 to 1075 deg C with diffusion couples of U with Zr, Mo, Ti, and Nb and with the alloys U--Nb and U--Mo. A brief description is given of the experimental methods. Results relative to the concentration-penetration curves are presented, and the coefficients of diffusion are calculated. The equilibrium diagram was established for the U--Zr system. The results obtained by micrographic examination, microhardness measurements, and autoradiography are compared with each other. The mechanisms of diffusion are investigated by studying the Kirkendall effect and calculating the Darken intrinsic coeffi cients in the U--Zr and U--UMo diffusion couples. (J.S.R.)
Date: October 31, 1959
Creator: Adda, Y. & Philibert, J.
Partner: UNT Libraries Government Documents Department

Hydrogen induced crack growth in Grade-12 titanium

Description: Internal hydrogen induced crack growth rates were measured in Grade-12 titanium which is a candidate material for high-level nuclear waste containers. As-received and hydrogen charged samples (5 ppM to 330 ppM hydrogen) were used for slow crack growth measurements at constant loads using a Krak Gauge. The testing temperature ranged from room temperature to 148/sup 0/C. The crack growth kinetics under low to moderate loads are linear, but this linear rate is interrupted by discrete fast crack jump segments with parabolic or cubic type kinetics. These fast jump segments are thought to be associated with the passage of the crack front through the alpha-beta interface phase or with the initial loading sequence. By measuring striation spacings on the fracture surface, most crack growth rates observed are found to be in stage II. The striations are considered to be associated with hydride fracture. The crack path is either transgranular in the alpha phase or interfacial in the alpha phase adjacent to the beta phase. For transgranular growth, crack growth rates are constant and slower than those for interfacial growth which is associated with fast crack growth through a high hydrogen concentration region. Most stage II crack growth rates depend slightly on the stress intensity suggesting the contribution of plastic tearing process to stage II kinetics. The activation energies for crack growth are much lower than the activation energy of hydrogen diffusion through the alpha phase, implying that hydrogen is transported along dislocations, grain boundaries or interfaces. When the temperature is increased, the crack velocity first reaches a maximum and then decreases at higher temperatures. These temperature effects come from lower hydrogen concentration trapped at dislocations or from slower hydride nucleation kinetics, both at higher temperatures.
Date: January 1, 1984
Creator: Ahn, T.M. & Lee, K.S.
Partner: UNT Libraries Government Documents Department

Radiation-induced alkali formation and its effect on the corrosion of Grade-12 titanium in rock salt nuclear waste repositories

Description: Natural rock salt was gamma irradiated at a dose rate of 8 x 10/sup 6/ rad/h for times up to 1338 h. Subsequent dissolution in water produced high pH solutions. The corrosion properties of ASTM Grade-12 titanium were evaluated in simulated alkaline rock salt brines. The uniform corrosion rates were enhanced compared to those for neutral solutions, but crevice corrosion rates were retarded because of difficulties in obtaining high acidity in the crevice region. Hydrogen uptake was enhanced because of the chemical dissolution of the oxide layer. Upon hydrogenation, tensile samples showed slow-strain-rate embrittlement. Stress corrosion cracking, however, was not detected in the alkaline brines. 23 references, 8 figures, 6 tables.
Date: January 1, 1985
Creator: Ahn, T.M. & Panno, S.V.
Partner: UNT Libraries Government Documents Department

Identification of crevice corrosion in the titanium alloy TiCode-12 in simulated rock salt brine at 150/sup 0/C. [Ti-0. 3Mo-0. 8Ni]

Description: TiCode-12 (Ti-0.3Mo-0.8Ni) is a prime corrosion-resistant material for high-level nuclear-waste containers which will be emplaced in mined geologic repositories such as those in rock salt. The crevice corrosion behavior of this alloy was investigated in simulated rock salt brine solutions at a temperature of 150/sup 0/C. A distinct corrosion product with a range of interference colors was observed in a mechanically simulated crevice after two to four-weeks' exposure. Low pH accelerated the reaction rate and deaerated solutions give less corrosion than aerated ones. Also, increasing specimen size, decreasing crevice gap, and preoxidation of the cathodic area gave more voluminous corrosion products inside the crevice. High temperature did not necessarily accelerate crevice corrosion. These results are consistent with those expected from macroscopic concentration cell formation accompanied by oxygen depletion, potential drop, and acidification inside the crevice. TEM and SEM techniques were extensively utilized to identify the film formed inside the crevice at each stage of the corrosion process. Based on the study, and pH and potential measurements inside the crevice of commercially pure titanium done by other workers, a mechanism for crevice corrosion in TiCode-12 has been developed. It involves the initial formation of compact anatase crystals inside the crevice.As the macroscopic cell develops further, it is postulated that either the anatase form of TiO/sub 2/ will transform to the lower oxide Ti/sub 3/O/sub 5/ and to the rutile form of TiO/sub 2/, or titanium dissolves into the solution after the breakdown of the protective film and subsequent hydrolysis takes place to form the lower oxide and the rutile form of TiO/sub 2/. The role of alloying elements (Mo and Ni) and dissolved solutes are discussed with respect to these postulations. 10 figures, 3 tables.
Date: January 1, 1982
Creator: Ahn, T.M.; Lee, B.S. & Soo, P.
Partner: UNT Libraries Government Documents Department

Alloy design and phase stability of the ternary alloy titanium-aluminum-niobium

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The authors have used high-precision electronic-structure and cluster-variational method (CVM) techniques to study aspects of alloy design involving the phase stability and ordering tendencies of the ternary system Ti-Al-Nb, and the correlation with these to changes in the electronic structure of these materials. This system is of great interest for aerospace applications due to its desirable mechanical properties and low densities. Total energies were computed for 18 binary and ternary bcc superstructures in order to derive parameters for CVM calculations, which showed important strong ordering tendencies in the alloy phase diagram as a function of temperature and alloy concentration. Structural optimization calculations were used to analyze structural instabilities for bcc, fcc, hcp, O-phase, and {omega}-phase structures. The authors discovered the mechanism for the role of Nb in the structural stability of the O-phase of the ternary intermetallic Ti{sub 2}AlNb. Calculations were also done to investigate the electronic properties associated with the structural stability of a related class of Laves Phase high-temperature structural materials NbCr{sub 2} and HfV{sub 2}.
Date: December 31, 1998
Creator: Albers, R.C.; Chen, Shao-Ping & Wills, J.M.
Partner: UNT Libraries Government Documents Department

Team one (GA/MCA) effort of the DOE 12 tesla coil development program

Description: The 1980 effort has been concentrated upon four major tasks: completion of the conceptual design of an ETF reactor compatible TF-coil employing helium bath cooled NbTi alloy conductor; procurement of conductor for the coil to be tested at the LLNL HFTF during FY 82; design of the test coil; and a series of relevant tests using the GA HFTF. The ETF TF-coil concept employs cabled NbTiTa/copper conductor, immersed in a helium bath subcooled to 2.5 K from a saturation temperature of 3 K. A saturated superfluid (He II) bath cooled option is also under consideration. Hoop, radial and circumferential bearing loads are borne by a multicomponent frame of stainless steel strips which surround the pancake (spiral) wound conductor. Magnetic Corporation of America is providing the 10 kA, three level, unsoldered, uninsulated Rutherford cable for the test coil. Meanwhile, at GA, a series of heat pulse/recovery tests are being performed upon samples of cabled conductor, at 2.5 - 3 K, and in the He II range. These tests will guide the test coil cryogenic design, and provide improved insight into results later obtained with that coil at Livermore. The 0.4 m I.D. x 1 m O.D. Test Coil has been designed. Its salient features are presented.
Date: September 1, 1980
Creator: Alcorn, J.S.
Partner: UNT Libraries Government Documents Department

Status of the GA/MCA 12 Tesla Coil Development Program

Description: The current status of the Team One effort of the DOE/OFE/D and T 12 Tesla Coil Development Program is presented. Subatmospheric, helium bath cooled, NbTiTa alloy is employed for the test coil, and ETF TF-coil concept. General Atomic is the Team One leader, with Magnetic Corporation of American as industrial subcontractor.
Date: September 1, 1980
Creator: Alcorn, J.S.; Purcell, J.R.; Chen, W.Y. & Hsu, Y.H.
Partner: UNT Libraries Government Documents Department

Team One (GA/MCA) effort of the DOE 12-tesla coil-development program. Quarterly progress report, April 1- June 30, 1980

Description: This report covers progress by Team One of the DOE/OFE/D and T 12 Tesla Coil Development Program during the third quarter fiscal period of 1980. The basic mission of this effort is to demonstrate the feasibility of, and to establish an engineering data base for employment of bath cooled NbTi alloy to generate a peak field of 12 tesla in a tokamak reactor. General Atomic Company is the leader of Team One, with the Magnetic Corporation of America as industrial subcontractor. Phase I, development of a NbTi alloy, compositionally and process optimized for 12 tesla operation at temperatures below 4 K, was completed during FY 1979. Phase II, conceptual design of an ETF reactor compatible TF-coil system, employing the NbTi alloy selected by Phase I and an appropriate bath cooling regime, was completed during this reporting period. Progress was also made during this period on Phase III of this effort: Design construction and testing of a solenoid coil utilizing the selected reactor prototypical conductor and bath conditions. During this reporting period, two Phase IV tests were made at the General Atomic High Field Test Facility. Recovery tests were performed upon cabled conductor samples at 3 K and under superfluid (He II) conditions. Results therefrom will be reported in the Fourth Quarter Progress Report of this effort.
Date: July 1, 1980
Creator: Alcorn, J.S.; Purcell, J.R.; Chen, W.Y. & Hsu, Y.H.
Partner: UNT Libraries Government Documents Department

In situ transmission electron microscope studies of irradiation-induced and irradiation-enhanced phase changes

Description: Motivated at least initially by materials needs for nuclear reactor development, extensive irradiation effects studies employing TEMs have been performed for several decades, involving irradiation-induced and irradiation-enhanced, microstructural changes, including phase transformations such as precipitation, dissolution, crystallization, amorphization, and order-disorder phenomena. From the introduction of commercial high voltage electron microscopes (HVEM) in the mid-1960s, studies of electron irradiation effects have constituted a major aspect of HVEM application in materials science. For irradiation effects studies two additional developments have had particularly significant impact: (1) The availability of TEM specimen holders in which specimen temperature can be controlled in the range 10--2200 K; and (2) the interfacing of ion accelerators which allows in situ TEM studies of irradiation effects and the ion beam modification of materials within this broad temperature range. This paper treats several aspects of in situ studies of electron and ion beam-induced and enhanced phase changes, including the current state of in situ ion beam capability internationally, and presents two case studies involving in situ experiments performed in an HVEM to illustrate the dynamics of such an approach in materials research.
Date: December 31, 1991
Creator: Allen, C. W.
Partner: UNT Libraries Government Documents Department

Irradiation-related amorphization and crystallization: In situ transmission electron microscope studies

Description: Interfacing an ion accelerator to a transmission electron microscope (TEM) allows the analytical functions of TEM imaging and diffraction to be employed during ion-irradiation effects studies. At present there are twelve such installations in Japan, one in France and one in the US. This paper treats several aspects of in situ studies involving electron and ion beam induced and enhanced phase transformations and presents results of several in situ experiments to illustrate the dynamics of this approach in the materials science of irradiation effects. The paper describes the ion- and electron-induced amorphization of CuTi; the ion-irradiation-enhanced transformation of TiCr{sub 2}; and the ion- and electron-irradiation-enhanced crystallization of CoSi{sub 2}.
Date: April 1, 1994
Creator: Allen, C. W.
Partner: UNT Libraries Government Documents Department

In situ transmission electron microscope studies of irradiation-induced and irradiation-enhanced phase changes

Description: Motivated at least initially by materials needs for nuclear reactor development, extensive irradiation effects studies employing TEMs have been performed for several decades, involving irradiation-induced and irradiation-enhanced, microstructural changes, including phase transformations such as precipitation, dissolution, crystallization, amorphization, and order-disorder phenomena. From the introduction of commercial high voltage electron microscopes (HVEM) in the mid-1960s, studies of electron irradiation effects have constituted a major aspect of HVEM application in materials science. For irradiation effects studies two additional developments have had particularly significant impact: (1) The availability of TEM specimen holders in which specimen temperature can be controlled in the range 10--2200 K; and (2) the interfacing of ion accelerators which allows in situ TEM studies of irradiation effects and the ion beam modification of materials within this broad temperature range. This paper treats several aspects of in situ studies of electron and ion beam-induced and enhanced phase changes, including the current state of in situ ion beam capability internationally, and presents two case studies involving in situ experiments performed in an HVEM to illustrate the dynamics of such an approach in materials research.
Date: January 1, 1991
Creator: Allen, C.W.
Partner: UNT Libraries Government Documents Department

Precipitation of krypton in an amorphous Ti-Cr alloy. [Ti-Cr Thin Films]

Description: Results of a TEM investigation of the microstructural changes produced by the room temperature implantation of energetic Kr/sup +/ ions into a glassy Ti-Cr thin film are reported. As in other metals, the Kr precipitates as solid crystallites. The precipitation of crystalline Kr is accompanied by ultrafine crystallization of the metal host around each Kr crystal. With increasing fluence, the Kr precipitates grow to a critical size at which they melt, and the adjacent fine metal crystals disappear. A new TEM imaging technique is described briefly which utilizes the small angle electron scattering fine structure and which in principle is capable of revealing all fine particles simultaneously.
Date: December 1, 1986
Creator: Allen, C.W. & Birtcher, R.C.
Partner: UNT Libraries Government Documents Department

A Model for Predicting Grain Boundary Cracking in Polycrystalline Viscoplastic Materials Including Scale Effects

Description: A model is developed herein for predicting the mechanical response of inelastic crystalline solids. Particular emphasis is given to the development of microstructural damage along grain boundaries, and the interaction of this damage with intragranular inelasticity caused by dislocation dissipation mechanisms. The model is developed within the concepts of continuum mechanics, with special emphasis on the development of internal boundaries in the continuum by utilizing a cohesive zone model based on fracture mechanics. In addition, the crystalline grains are assumed to be characterized by nonlinear viscoplastic mechanical material behavior in order to account for dislocation generation and migration. Due to the nonlinearities introduced by the crack growth and viscoplastic constitution, a numerical algorithm is utilized to solve representative problems. Implementation of the model to a finite element computational algorithm is therefore briefly described. Finally, sample calculations are presented for a polycrystalline titanium alloy with particular focus on effects of scale on the predicted response.
Date: April 6, 1999
Creator: Allen, D. H.; Helms, K. L. E. & Hurtado, L. D.
Partner: UNT Libraries Government Documents Department

Damage evolution in metal matrix composites subjected to thermomechanical fatigue

Description: A thermomechanical analysis of unidirectional continuous fiber metal matrix composites is presented. The analysis includes the effects of processing induced residual thermal stresses, interface cracking, and inelastic matrix behavior on damage evolution. Due to the complexity of the nonlinear effects, the analysis is performed computationally using the finite element method. The interface fracture is modeled by a nonlinear constitutive model. The problem formulation is summarized and results are presented for a four-ply unidirectional SCS-6/{beta}21S titanium composite under high temperature isothermal mechanical fatigue.
Date: May 1, 1995
Creator: Allen, D.H.; Hurtado, L.D. & Helms, K.L.E.
Partner: UNT Libraries Government Documents Department

Models for predicting damage evolution in metal matrix composites subjected to cyclic loading

Description: A thermomechanical analysis of a continuous fiber metal matrix composite (MMC) subjected to cyclic loading is performed herein. The analysis includes the effects of processing induced residual thermal stresses, matrix inelasticity, and interface cracking. Due to these complexities, the analysis is performed computationally using the finite element method. Matrix inelasticity is modelled with a rate dependent viscoplasticity model. Interface fracture is modelled by the use of a nonlinear interface constitutive model. The problem formulation is summarized, and results are given for a four-ply unidirectional SCS-6/{beta}21S titanium composite under high temperature isothermal mechanical fatigue. Results indicate rate dependent viscoplasticity can be a significant mechanism for dissipating the energy available for damage propagation, thus contributing to improved ductility of the composite. Results also indicate that the model may be useful for inclusion in life prediction methodologies for MMC`s.
Date: March 1, 1995
Creator: Allen, D.H.; Hurtado, L.D. & Helms, K.L.E.
Partner: UNT Libraries Government Documents Department

Slip, twinning and transformation in Laves phases. [Ti-TiCr[sub 2]; Fe-ZrFe[sub 2]; Ni-Cu-Mg containing MgNi[sub 2] and MgCu[sub 2]]

Description: Research was concentrated on two-phase Ti-TiCr[sub 2] alloys, two- phase Fe-ZrFe[sub 2] alloys, and two-phase ternary Ni-Cu-Mg alloys containing MgNi[sub 2] and MgCu[sub 2] phases. Work demonstrated that a variety of room-temperature deformation processes are possible in Laves phases. A strain-induced phase transformation from C36[r arrow]C15 structures is one mechanism for plastic deformation in ZrFe[sub 2]. The C15 structure in TiCr[sub 2] deforms by slip and twinning. The microstructure after indentation of specimens containing C36 phases ZrFe[sub 2] and MgNi[sub 2] indicates that a variety of slip systems operate in this form. 8 figs.
Date: January 26, 1993
Creator: Allen, S.M. & Livingston, J.D.
Partner: UNT Libraries Government Documents Department

An in situ transmission electron microscopy study of the thermalstability of near-surface microstructures induced by deep rolling andlaser-shock peening

Description: Mechanical surface treatments are known to be effective at improving the fatigue resistance of metallic alloys at elevated temperatures ({approx}550-600 C), even though the near-surface compressive residual stress fields have been annealed out. We have investigated the thermal stability of near-surface microstructures induced by deep rolling and laser-shock peening in an austentic stainless steel (AISI 304) and a titanium alloy (Ti-6Al-4V) using in situ hot-stage transmission electron microscopy. It is found that the improvements in fatigue resistance at elevated temperature are related to the high-temperature stability of the work-hardened near-surface microstructure in each case.
Date: February 24, 2003
Creator: Altenberger, I.; Stach, E.A.; Liu, G.Y.; Nalla, R.K. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

Surface and microstructural characterization of commercial breeder reactor candidate alloys exposed to 700/sup 0/C sodium

Description: Sodium compatibility screening tests were performed on several commercial austenitic alloys at 700/sup 0/C for 2000 hours for applications as breeder reactor fuel cladding. The sodium-exposed surfaces were characterized by Optical Metallography, Scanning Electron Microscopy (SEM) and Electron Probe Micro Analysis (EPMA). Sodium exposure generally resulted in the depletion of Ni, Cr, Ti, Si, Mn and Nb, and enrichment of Fe and Mo at the surface. The average thickness of the depleted zone was 5 ..mu..m. The alloys can be divided into three groups based on corrosion rate, and each group has its own characteristic surface structure. Grain-orientation dependent striations were seen in alloys with low corrosion rates, while alloys with intermediate corrosion rates displayed micron-size nodes enriched with Fe and Mo. The high corrosion rate alloys exhibited scale-like formations on the surface with irregularly shaped holes. In addition, the data importantly point out that a ferrite layer will form at the sodium-exposed surface of these austenitic alloys after prolonged exposure.
Date: March 1, 1979
Creator: Anantatmula, R.P. & Brehm, W.F.
Partner: UNT Libraries Government Documents Department

In-sodium creep behavior of alloys M-813 and Nimonic PE16

Description: The in-sodium biaxial creep deformation of internally pressurized tube specimens of alloys M-813 and Nimonic PE16 was measured at 650/sup 0/C under constant stress conditions after 4000 hours of sodium exposure. Each alloy had specimens at two different stress levels, viz., 0 and 165 MPa (24,000 psi). The data showed negative diameter changes at zero stress, which were attributed to material densification associated with precipitation. Although material densification was also seen in comparable in-argon experiments, the in-sodium creep strains at 165 MPa and 650/sup 0/C were much lower than the corresponding in-argon values. The higher creep strains in argon are explained on the basis of two parallel mechanisms involving oxygen, which is present at a low level in sodium (1 ppM) as compared with approximately 1000 ppM in the argon environment. The trends in the current data are consistent with observations by earlier authors. Sodium exposure of Nimonic PE16 also resulted in 4 ..mu..m deep intergranular penetration, which did not have any apparent effect on its biaxial creep behavior.
Date: April 1, 1980
Creator: Anantatmula, R.P. & Gilbert, E.R.
Partner: UNT Libraries Government Documents Department

Microstructural characterization of advanced ferrous alloys exposed to liquid sodium. [700/sup 0/C for 2000 hours]

Description: The property requirements for breeder reactor fuel cladding materials are extremely stringent. Alloys with low sodium corrosion rates are required to avoid loss of strength from wall thinning at reactor operating temperatures. Data obtained on the following alloys are described: A-286, Inconel 706, Nimonic PE16, AISI 316, M-813 (sintered), Inconel 718, AISI 310, and Alloy 330. Tests were carried out at 700/sup 0/C for 2000 hours at a sodium velocity of 6 m/s and an oxygen content in sodium of 1 ppM. Corrosion rates and major elements depleted are tabulated. It is concluded that A-286, Inconel 706, and Nimonic PE16 are highly promising commercial alloys for cladding purposes on the basis of corrosion resistance. 5 figures, 1 table. (RWR)
Date: July 1, 1977
Creator: Anantatmula, R.P.; Mayhan, S.J. & White, P.A.
Partner: UNT Libraries Government Documents Department

Ultrasonic texture characterization of aluminum, zirconium and titanium alloys

Description: This work attempts to show the feasibility of nondestructive characterization of non-ferrous alloys. Aluminum alloys have a small single crystal anisotropy which requires very precise ultrasonic velocity measurements for derivation of orientation distribution coefficients (ODCs); the precision in the ultrasonic velocity measurement required for aluminum alloys is much greater than is necessary for iron alloys or other alloys with a large single crystal anisotropy. To provide greater precision, some signal processing corrections need to be applied to account for the inherent, half-bandwidth offset in triggered pulses when using a zero-crossing technique for determining ultrasonic velocity. In addition, alloys with small single crystal anisotropy show a larger dependence on the single crystal elastic constants (SCECs) when predicting ODCs which require absolute velocity measurements. Attempts were made to independently determine these elastics constants in an effort to improve correlation between ultrasonically derived ODCs and diffraction derived ODCs. The greater precision required to accurately derive ODCs in aluminum alloys using ultrasonic nondestructive techniques is easily attainable. Ultrasonically derived ODCs show good correlation with derivations made by Bragg diffraction techniques, both neutron and X-ray. The best correlation was shown when relative velocity measurements could be used in the derivations of the ODCs. Calculation of ODCs in materials with hexagonal crystallites can also be done. Because of the crystallite symmetries, more information can be extracted using ultrasonic techniques, but at a cost of requiring more physical measurements. Some industries which use materials with hexagonal crystallites, e.g. zirconium alloys and titanium, have traditionally used texture parameters which provide some specialized measure of the texture. These texture parameters, called Kearns factors, can be directly related to ODCs.
Date: October 8, 1997
Creator: Anderson, A.J.
Partner: UNT Libraries Government Documents Department