Superconductivity: A new window on plutonium’s complexity

Superconductivity has recently been discovered in a plutonium intermetallic compound (PuCoGa₅) at the surprisingly high temperature of 18.5 K. This article discusses the motivation that led to this discovery as well as what it implies for the understanding of both unconventional superconductivity and the metallurgy of plutonium. For more information, contact J.L. Sarrao, Los Alamos National Laboratory, MST-10: Condensed Matter & Thermal Physics, Mail Stop K764, Los Alamos, NM 87545; (505) 665-0481; fax (505) 665-7652; e-mail sarrao@lanl.gov.     

Developing impact and fatigue damage prognosis solutions for composites

An approach to developing a damage prognosis solution that integrates advanced sensing technology, data interrogation procedures for damage detection, novel model validation and uncertainty quantification techniques, and reliability-based decision-making algorithms is summarized in this article. In parallel, experimental efforts are underway to deliver a proof-of-principle technology demonstration by assessing impact damage and predicting the subsequent fatigue damage accumulation in a composite plate. This article provides an overview of the various technologies that are being integrated to address this damage prognosis problem. Editor’s Note: Presentation of this paper is supported by the Air Force Research Laboratory, under agreement number F33615-01-D-5801. The U.S. Government is authorized to reproduce and distribute reprints for governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the Air Force Research Laboratory or the U.S. Government. For more information, contact Charles Farrar, Los Alamos National Laboratory, MST-006, Los Alamos, NM 87545; e-mail farrar@lanl.gov.     

A brief history of TEM observations of plutonium and its alloys

Transmission electron microscopy (TEM) has proven to be a useful tool to investigate the morphological and crystallographic nature of plutonium metal and alloys. Its unique ability to provide direct visual as well as crystallographic information on a very fine scale has given new insight into the complex nature of plutonium. Because of the limited number of TEM observations performed to date, there is little doubt that this metal’s most intriguing microstructural secrets are yet to be revealed. For more information, contact T.G. Zocco, Los Alamos National Laboratory, NMT-10, Manufacturing Process Science and Technology Group, P.O. Box 1663, Mail Stop E506, Los Alamos, NM 87545; (505) 667-4481; fax (505) 667-8528; e-mail zocco@lanl.gov.     

Metal forming at the center of excellence for the synthesis and processing of advanced materials

The U.S. Department of Energy’s Office of Basic Energy Sciences recently established the Center for Excellence in the Synthesis and Processing of Advanced Materials. Projects at the center typically include several national laboratories, industrial partners, and universities; metal forming is one of eight projects within the center. This article describes the center’s metal forming project, which emphasizes aluminum alloy forming, particularly as applicable to the automotive industry. D.A. Hughes earned her Ph.D. in materials science at Stanford University in 1986. She is a principal member of the technical staff at Sandia National Laboratories. M.E. Kassner earned his Ph.D. in materials science at Stanford University in 1981. He is Northwest Aluminum Professor at Oregon State University. M.G. Stout earned his Ph.D. in materials science at the University of Minnesota in 1976. He is a staff member at Los Alamos National Laboratory. J. Vetrano earned his Ph.D. in metallurgy at the University of Illinois in 1990. He is a senior research scientist at Pacific Northwest National Laboratory. Editor’s Note: A hypertext-enhanced version of this article can be found on the TMS web site at www.tms.org/pubs/joumals/JOM/9806/Hughes-9806.html.     

The corrosion of materials in spallation neutron sources

Efforts to measure the real-time corrosion rates of alloy 718 during 800 MeV proton radiation at currents up to 1 mA are reported. Specially designed corrosion probes, which incorporate ceramic seals, were mounted in a water manifold that allowed samples to be directly exposed to the proton beam at the Los Alamos Neutron Science Center. The water system that supplied the manifold provided a means for controlling water chemistry, measuring dissolved hydrogen concentration, and measuring the effects of water radiolysis and water quality on corrosion rate. Real-time corrosion rate measurements during proton irradiation showed an exponential increase in corrosion rate with proton-beam current. These results are discussed within the context of water radiolysis at the diffusion boundary layer/beam-spot interface. However, additional factors that may influence these parameters, such as oxide spallation and charge build-up in the passive film, are not ruled out. Scott Lillard earned his Ph.D. in materials science and engineering from Johns Hopkins University in 1992. He is currently a technical staff member at the Materials Corrosion and Environmental Effects Laboratory, Los Alamos National Laboratory. Darryl P. Butt earned his Ph.D. in ceramic science from Pennsylvania State University in 1991. He is currently a technical staff member at the Non-Proliferation and International Security Division, Los Alamos National Laboratory.     

Using the modified embedded-atom method to calculate the properties of Pu-Ga alloys

In this article, the semi-empirical modified embedded atom method is used to develop a model of Pu-Ga alloys. Employing classical calculations, the model is used to predict thermodynamic properties of these alloys as well as the complex Pu-Ga phase diagram. For more information contact M.I. Baskes, Los Alamos National Laboratory, P.O. Box 1663, MS-G755, Los Alamos, NM 87545, USA; (505) 667-1238; fax (505) 667-8021; baskes@lanl.gov.     

Plutonium: Coping with instability

Plutonium is unstable with time because of its radioactive decay, but it is the peculiar nature of its electronic structure that gives rise to phase instability with temperature, pressure, and chemical additions, making engineering applications particularly challenging. This instability leads to an interesting array of phase transformations and microstructures. For more information, contact Siegfried S. Hecker at the Los Alamos National Laboratory, Materials Science and Technology Division, MS G754, Los Alamos, NM 87545; (505) 665-6601; fax (505) 665-4584; e-mail sh@lanl.gov.     

An atomistic study of solid/liquid interfaces in binary systems

In this study, a semi-empirical Lennard-Jones/embedded atom method model is used to capture real materials behavior through the introduction of many-body forces. By means of molecular dynamics calculations, the model is used to study the dependence of the solid-liquid interface velocity on temperature for two alloy compositions. For more information contact M.I. Baskes, Los Alamos National Laboratory, PO Box 1663, MS-G755, Los Alamos, NM 87545, USA; (505) 667-1238; fax (505) 667-8021; baskes@lanl.gov.     

Understanding the unique properties of SPD-induced microstructures

Refining microstructure by severe plastic deformation to a nanometer range changes fundamental properties, such as the Curie and Debye temperatures, and engineering properties of pragmatic significance, such as strength and ductility. These enhancements originate in the combination of very small grain sizes coupled with specific defect structures. Ongoing research is rapidly advancing the understanding of severe plastic deformation-induced microstructures, leading toward the commercialization of these materials. For more information, contact T.C. Lowe, Los Alamos National Laboratory, Materials Science and Technology Division, MD G754, Los Alamos, New Mexico 87545; (505) 665-1131; fax (505) 665-4584; e-mail tlowe@lanl.gov. Authors’ Note: All compositions are given in weight per cent.     

Applying the two-state invar model to delta-phase plutonium

This article describes the authors’ use of the Weiss two-state model for Fe-Ni invar alloys to understand the anomalous thermal expansion of Pu-Ga alloys. Studies on thermal expansion of Pu-Ga are reviewed briefly, and the two-state invar model is described. The authors fit the available neutron-diffraction data for Pu-Ga alloys to the invar model and discuss the consequences. For more information, contact Andrew C. Lawson, Structure and Properties Group: MST-8, MS H-805, Los Alamos National Laboratory, Los Alamos, New Mexico 87545; (505) 667-8844; fax (505) 665-2676; e-mail lawson@lanl.gov.     

The fundamentals of nanostructured materials processed by severe plastic deformation

Nanostructured materials produced by severe plastic deformation (SPD) are 100% dense, contamination-free, and sufficiently large for use in real commercial structural applications. These materials are found to have high strength, good ductility, superior superplasticity, a low friction coefficient, high wear resistance, enhanced high-cycle fatigue life, and good corrosion resistance. This article reviews the structures and properties of nanostructured materials produced by SPD and reports recent progress in determining the deformation mechanisms that lead to these superior mechanical properties. For more information, contact Yuntian T. Zhu, Los Alamos National Laboratory, Materials Science and Technology Division, Los Alamos, NM 87545; (505) 667-4029; fax (505) 667-2264; e-mail yzhu@lanl.gov.     

Stability and thermodynamic properties of supersaturated solid solution and amorphous phase formed by ball milling in the Zr- Al system

Zr ₁₀₀-_xA1_x (x ≤ 40) metastable alloys were synthesized by high- energy ball milling of elemental Zr and Al powders: supersaturated substitutional cph solid solution for x ≤ 15 and an amorphous phase for x ≥ 17.5. We performed a calorimetric study of the thermodynamics and kinetics of the metastable- to- equilibrium transformations of these phases. Their stability range (temperature/composition), as well as the apparent activation energies associated with the transformations, were determined. The transformation enthalpies were measured and used to determine the enthalpy of formation for these metastable phases. For both as- milled and relaxed amorphous phases, the measured enthalpy of crystallization is compared with those estimated for an undercooled liquid. Different amounts of retained entropy at the glass transition temperature were used to estimate the enthalpy loss upon undercooling due to the excess specific heat. This paper was presented at the Thermodynamics and Phase Equilibria of Metastable Phases Symposium at the Spring TMS Meeting, March 1-4,1992, in San Diego. The symposium was organized by Philip Nash, Illinois Institute of Technology, and Ricardo Schwarz, Los Alamos National Laboratory.     

The use of severe plastic deformation techniques in grain refinement

Severe plastic deformation (SPD) has emerged as a promising method to produce ultrafine-grained materials with attractive properties. Today, SPD techniques are rapidly developing and are on the verge of moving from lab-scale research into commercial production. This paper discusses new trends in the development of SPD techniques suchas high-pressure torsion and equal-channel angle pressing, as well as new alternative techniques for introducing SPD. The paper also contains a comparative analysis of SPD techniques in terms of their relative capabilities for grain refinement, enhancement of properties, and potential to economically produce ultrafine-grained metals and alloys. For more information, contact Terry C. Lowe, Science and Technology Base Programs, Los Alamos National Laboratory, Los Alamos, NM 87545; (505) 667-7824; fax (505) 665-3199; e-mail tlowe@lanl.gov.     

Truchas – a multi-physics tool for casting simulation

Abstract

The Truchas code was developed at Los Alamos National Laboratory under the Advanced Simulation and Computing Program. This open source multi-physics simulation software is designed to run in a scalable parallel computing environment. The capabilities of the code and numerical implementation are briefly described. The advantages and limitations of large three dimensional simulations will be discussed, and two example simulations are shown that demonstrate the utility of the fluid flow, heat transfer, phase change and solid mechanics capabilities. Validation of a code such as Truchas is a difficult task because of the complexity of the coupling between different physical phenomena being modelled and the poor understanding of phenomena such as heat transfer across interfaces. The challenges associated with verification and validation of complex simulation tools and integration into the design process are also discussed.     

The effect of retrogression and reaging on the properties of the 7249 aluminum alloy

The retrogression and reaging (RRA) heat-treatment process and recent developments in high-strength 7xxx series aluminum alloys are summarized in this article. The results of experimental work indicate that RRA 7249 aluminum has the strength equivalent to or greater than 7249-T6 and superior corrosion resistance. This work is the result of collaborative efforts between the U.S. Navy and Loyola Marymount University. For more information contact Omar S. Es-Said, Mechanical Engineering Department, Loyola Marymount University, 7900 Loyola Blvd. Los Angeles, CA, 90045; (310) 338-2829; fax (310) 338-2391; e-mail oessaid@lmu.edu.     

Engineering Applications of Time-of-Flight Neutron Diffraction

Time-of-flight neutron diffraction is widely used in characterizing the microstructure and mechanical response of heterogeneous systems. Microstructural characterization techniques include spatial or temporal mapping of the phases and determination of grain size, dislocation structure, and grain orientations (texture) within these phases. Mechanical response analysis utilizes the crystallographic selectivity of the diffraction process to measure the partitioning of strain within the system. The microstructural and mechanical response information is then used to develop more realistic constitutive models. In this article we review some examples of such measurements, based on our experiences at the Lujan Center of Los Alamos National Laboratory.     

The Nb-Pu (niobium-plutonium) system

Work supported by a contract from Los Alamos National Laboratory, Lawrence Livermore National Laboratory, and ASM International. Literature searched through September 1991.     

Analyzing and characterizing the steel used at frank lloyd wright’s fallingwater

Conclusions When Frank Lloyd Wright designed Fallingwater, he must not have specified a steel grade or condition that varied from common production available. Yet, it is notable that the Bessemer steel reinforcing bar had not deteriorated during service in the concrete terrace. Also, the open-hearth hatch steel performed well, as severe corrosion occurred only at the concrete-bar interface while the remainder of the flat bar, also exposed above the Bear Run stream for 68 years, showed only pitting corrosion. Fallingwater has timeless interest as an architectural achievement, and some of the steel used to produce this landmark was made using techniques whose time has passed. Editor’s Note: A hypertext-enhanced version of this article can be found at www.tms.org/pubs/journals/JOM/0303/Dean0303.html. Author’s note: The units are both metric and U.S. customary, as the publications and the steel sections referred to used U.S. customary units. For more information, contact Louise Dean, Westmoreland Mechanical Testing & Research, PO Box 388, Youngstown, PA. 15696-0388; (724) 537-3131; e-mail louise@stargate.net.     

How Roebling did it: Building the world's first wire-rope suspension aqueduct in 1840s Pittsburgh

The noted bridge designed John Roebling introduced his wire-rope suspension concept in Pittsburgh on a wooden aqueduct. His design was later implemented in bridges in Pittsburgh and elsewhere, including New York's Brooklyn Bridge. This article describes Roebling's work based on reviews of his notes and other historical documents. Editor's Note: In the interest of consistency with historical documents, all units of measure are presented in U.S. rather than metric units. A hypertext-enhanced version of this article is available on-line at www.trns.org/pubs/journals/JOM/0605/Gibbon-0605.html.     

The alpha prime to delta reversion transformation in Pu-Ga alloys

The α′→δ reversion transformation in stabilized δ phase Pu-Ga alloys containing 0.5 wt.% and 0.6 wt.% Ga was studied using dilatometry and differential scanning calorimetry. The α′→δ reversion was observed to occur as a series of transformation bursts spread over a 20°C to 40°C temperature range. The enthalpy of the endothermic α′→δ reversion transformation was estimated to be approximately 0.56 J/g for the 0.6 wt.% Ga alloy. Lower gallium was found to raise the α′→δ reversion temperature in specimens cooled to −155°C from 44–48°C for 0.6 wt.% Ga to 92°C for 0.5 wt.% Ga. Repeated cycling to −155°C caused the reversion onset temperature to decrease by ∼10°C. Raising the minimum hold temperature from −150°C to −125°C caused the reversion onset temperature to decrease by 5–10°C. Annealing at 300–400°C was required to erase all traces of the effects of cold exposure; material heated to only 200°C after thermal cycling displayed decreased reversion onset temperatures during subsequent thermal cycling. For more information, contact D.S. Schwartz, Los Alamos National Laboratory, NMT Division, Los Alamos, New Mexico 87545.