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Polycrystal Simulations of Texture Evolution during Deformation Processing

Description: Some recent research on the hot deformation of aluminum alloys has indicated that at elevated temperatures, slip occurs on {110}<110> systems in addition to the usual {111}<110> systems active at lower temperatures. The effect of these additional slip systems on the texture evolution of aluminum single and polycrystals is studied using finite element simulations. The crystals are deformed in plane strain compression, and the constitutive response is modeled using crystal plasticity to track the reorientation of the crystals. By discretizing each crystal with a large number of elements, the non-uniform deformations due to local inhomogeneities and interactions with neighboring crystals are modeled. The resulting textures and microstructures are examined with regard to effect of including the additional systems, initial orientation of the single crystals, and stability of the cube orientation.
Date: May 11, 1998
Creator: Radhakrishnan, B.; Sarma, G. & Zacharia, T.
Partner: UNT Libraries Government Documents Department

A correlation between EIS and salt spray proof tests for the corrosion resistance of conversion coated aluminum alloys

Description: In this study, 33 different conversion coatings were applied to 5 different Al alloy substrates. Salt spray exposure testing and EIS (electrochemical impedance spectroscopy) were conducted for comparison. A relation was developed.
Date: September 1, 1996
Creator: Buchheit, R.G.; Martinez, M.A.; Cunningham, M.; Jensen, H. & Kendig, M.W.
Partner: UNT Libraries Government Documents Department

Light weight cellular structures based on aluminium

Description: An interesting form of lightweight material which has emerged in the past 2 decades is metallic foam. This paper deals with the basic concepts of making metallic foams and a detailed study of foams produced from Al-SiC. In addition, some aspects of cellular solids based on honeycomb structures are outlined including the concept of producing both two-phase foams and foams with composite walls.
Date: February 1, 1997
Creator: Prakash, O.; Embury, J.D.; Sinclair, C.; Sang, H. & Silvetti, P.
Partner: UNT Libraries Government Documents Department

Synthesis, characterization and mechanical properties of nanocrystalline NiAl

Description: Nanocrystalline NiAl was produced from pre-cast alloys using an electron beam inert gas condensation system. In-situ compaction was carried out at 100-300 C under vacuum conditions. Energy dispersive spectroscopy was used to determine chemical composition and homogeneity. Average grain sizes in the range 4-10 nm were found from TEM dark field analyses. A compression-cage fixture was designed to perform disk bend tests. These tests revealed substantial room temperature ductility in nanocrystalline NiAl, while coarse grained NiAl showed no measurable room temperature ductility.
Date: November 1, 1996
Creator: Choudry, M.; Eastman, J.A.; DiMelfi, R.J. & Dollar, M.
Partner: UNT Libraries Government Documents Department

Mechanical response and microcrack formation in a fine-grained duplex TiAl at different strain rates and temperatures

Description: Compressive behavior of this alloy was studied at strain rates of 0. 001 and 2000 sec{sup -1} and temperatures from -196 C to 1200 C. Temperature dependence of yield stress was found to depend on strain rate: At the quasi-static strain rate, 0.001 sec{sup -1}, the yield stress decreases with temperature with a plateau between 200 and 800 C. At the high strain rate, 2000 sec{sup -1}, the yield stress exhibits a positive temperature dependence above 600 C. Strain hardening rate decreases dramatically with temperature in the very low and high temperature regions with a plateau at intermediate temperatures for both strain rates. As the strain rate increases, the strain hardening rate plateaus extended to higher temperatures. The strain rate sensitivity increases slightly with temperature (but less than 0.1) for strain rates above 0.001 sec{sup -1}. However, at a strain rate of 0.001 sec{sup -1}, there is a dramatic increase in the strain rate sensitivity with temperature; above 1100 C, the rate sensitivity becomes much larger. Microcracks occurring in grain interiors and at grain boundaries were observed at all strain rates and temperatures. Formation and distribution of microcracks were found to vary depending on strain rate and deformation temperature.
Date: October 1996
Creator: Jin, Z.; Cady, C.; Gray, G. T., III & Kim, Y.-W.
Partner: UNT Libraries Government Documents Department

Modeling of the recrystallization textures of Al-alloys after hot deformation

Description: The recrystallization textures of Al-alloys can be explained by a growth selection of grains with an approximate 40{degree}<111> orientation relationship out of a limited spectrum of preferentially formed nucleus orientations. Accordingly, recrystallization textures can be modeled by the multiplication of a function f(g){sup nucl} describing the probability of nucleation of the various orientations with a function f(g){sup grow} representing their growth probability. Whereas the growth probability can be accounted for by a 40{degree}<111> transformation of the rolling texture, the nucleation probability of the respective grains is given by the distribution of potential nucleus orientations, which is known from local texture analysis for the most important nucleation sites in rolled Al-alloys, cube-bands, grain boundaries and second-phase particles. The contribution of each of these nucleation sites are determined according to an approach to calculate the number of nuclei forming at each nucleation site, which is based on microstructural investigations on the evolution of the various nucleation sites during deformation. The paper describes the model for recrystallization texture simulation in Al-alloys and gives examples of recrystallization textures of AA3004 deformed in plane strain compression at a variety of different deformation temperatures and strain rates.
Date: December 1, 1998
Creator: Engler, O. & Vatne, H.E.
Partner: UNT Libraries Government Documents Department

On the importance of target materials interfaces during low speed impact

Description: We are conducting a Cooperative Research and Development Project under the sponsorship of the U.S. Department of Energy to determine the applicability of aluminum particulate reinforced alloy laminates to aircraft structures and for containment of aircraft engine turbine blades and debris due to catastrophic engine failure. Within this framework, we are studying the terminal interaction of projectiles impacting targets at speeds of 150- to 500 m/s. Our presentation focuses on a special series of experiments and computational physics analyses of 6061-T6 aluminum alloy targets in single plate and laminate form impacted by steel cylindrical projectiles. Four cases are examined, projectile impact into (1) a single plate, (2) three contiguous plates (frictional interfaces), (3) three contiguous plates separated by Teflon layers (frictionless interfaces), and (4) a spaced array of three plates. We found that the ratio of projectile kinetic energies just at target perforation for the highest to lowest critical projectile speeds over the four targets is 1.75. Considering that target areal density is held constant across the four targets, this is a dramatic result. 2 refs., 7 figs.
Date: July 1996
Creator: Gogolewski, R. P.; Cunningham, B. J.; Riddle, R.; Lesuer, D. & Syn, C.
Partner: UNT Libraries Government Documents Department

Stress Voiding in IC Interconnects - Rules of Evidence for Failure Analysts

Description: Mention the words ''stress voiding'', and everyone from technology engineer to manager to customer is likely to cringe. This IC failure mechanism elicits fear because it is insidious, capricious, and difficult to identify and arrest. There are reasons to believe that a damascene-copper future might be void-free. Nevertheless, engineers who continue to produce ICs with Al-alloy interconnects, or who assess the reliability of legacy ICs with long service life, need up-to-date insights and techniques to deal with stress voiding problems. Stress voiding need not be fearful. Not always predictable, neither is it inevitable. On the contrary, stress voids are caused by specific, avoidable processing errors. Analytical work, though often painful, can identify these errors when stress voiding occurs, and vigilance in monitoring the improved process can keep it from recurring. In this article, they show that a methodical, forensics approach to failure analysis can solve suspected cases of stress voiding. This approach uses new techniques, and patiently applies familiar ones, to develop evidence meeting strict standards of proof.
Date: September 17, 1999
Partner: UNT Libraries Government Documents Department

ALCAR - A Model for Horizontal R&D Consortia

Description: The ALCAR<sup>TM</sup> Consortium was created to develop a low cost, non-heat treatable automotive body sheet alloy. This paper will discuss the management aspects of organizing and running a horizontal consortium for competing companies to cooperate in conducting pre-competitive research and development involving the US Department of Energy, National Laboratories, Universities and industrial consultants.
Date: March 1999
Creator: Barthold, G. B.; Das, S. K. & Hayden, H. W.
Partner: UNT Libraries Government Documents Department

Calcium metal as a scavenger for antimony from aluminum alloys

Description: Previous work has shown that trace amounts of antimony (Sb) can affect the mechanical properties of strontium (Sr) modified aluminum castings. ANL has been investigating technology to remove or neutralize Sb to reduce its negative effect on the physical properties of those alloys. Review of past work on processing and recovery of scrap aluminum inferred that calcium (Ca) is an effective scavenger of Sb, bismuth, lead and cadmium. Following up on that lead, we have found that Ca is, indeed, effective for removing Sb from molten aluminum alloys although its effectiveness can be compromised by a wide range of processing conditions. A minimum ratio of about four to one, by weight, of Ca to Sb appears necessary to insure an effective scavenging of contained Sb.in 356 aluminum alloys.
Date: October 4, 1994
Creator: Bonsignore, P.V.; Daniels, E.J. & Wu, C.T.
Partner: UNT Libraries Government Documents Department

Effect of heat treatment temperature on creep-rupture properties of Fe{sub 3}Al-based alloys

Description: The effects of heat treatment at 1100 to 1250C on the creep-rupture properties of an Fe{sub 3}Al-based alloy were studied. Tests were conducted at 593C (1100F) and 207 MPa (30 ksi) in air. The modes of fracture were identified using optical metallography and scanning electron microscopy. Analytical electron microscopy was also used to study characteristics of the microstructure, including dislocations, ordered domains, and precipitates. The creep results showed maximum creep-rupture resistance with a heat treatment at approximately 1150C, with significant decreases in rupture life after heat treatments at both lower and higher temperatures. The peak in creep life was associated with fine precipitates that were observed after the 1150C heat treatment and persisted during prolonged creep at 593C. Heat treatment at 1150C appeared to cause dissolution of coarser precipitates which then reprecipitated as new fine particles upon cooling or during creep. These fine precipitates then pinned dislocations and grain boundaries to produce strength during creep.
Date: September 1, 1994
Creator: McKamey, C. G. & Maziasz, P. J.
Partner: UNT Libraries Government Documents Department

Laser welding of automotive aluminum alloys to achieve defect-free, structurally sound and reliable welds

Description: The objective of this program was to seek improved process control and weldment reliability during laser welding of automotive aluminum alloys while retaining the high speed and accuracy of the laser beam welding process. The effects of various welding variables on the loss of alloying elements and the formation of porosity and other geometric weld defects such as underfill and overfill were studied both experimentally and theoretically.
Date: November 17, 2000
Creator: DebRoy, T.
Partner: UNT Libraries Government Documents Department

Reduction of Oxidative Melt Loss of Aluminum and Its Alloys

Description: This project led to an improved understanding of the mechanisms of dross formation. The microstructural evolution in industrial dross samples was determined. Results suggested that dross that forms in layers with structure and composition determined by the local magnesium concentration alone. This finding is supported by fundamental studies of molten metal surfaces. X-ray photoelectron spectroscopy data revealed that only magnesium segregates to the molten aluminum alloy surface and reacts to form a growing oxide layer. X-ray diffraction techniques that were using to investigate an oxidizing molten aluminum alloy surface confirmed for the first time that magnesium oxide is the initial crystalline phase that forms during metal oxidation. The analytical techniques developed in this project are now available to investigate other molten metal surfaces. Based on the improved understanding of dross initiation, formation and growth, technology was developed to minimize melt loss. The concept is based on covering the molten metal surface with a reusable physical barrier. Tests in a laboratory-scale reverberatory furnace confirmed the results of bench-scale tests. The main highlights of the work done include: A clear understanding of the kinetics of dross formation and the effect of different alloying elements on dross formation was obtained. It was determined that the dross evolves in similar ways regardless of the aluminum alloy being melted and the results showed that amorphous aluminum nitride forms first, followed by amorphous magnesium oxide and crystalline magnesium oxide in all alloys that contain magnesium. Evaluation of the molten aluminum alloy surface during melting and holding indicated that magnesium oxide is the first crystalline phase to form during oxidation of a clean aluminum alloy surface. Based on dross evaluation and melt tests it became clear that the major contributing factor to aluminum alloy dross was in the alloys with Mg content. Mg was identified as the ...
Date: March 17, 2006
Creator: Das, Dr. Subodh K. & Ningileri, Shridas
Partner: UNT Libraries Government Documents Department

Dynamics of metal/ceramic interface formation.

Description: We summarize the work of the Laboratory Directed Research and Development (LDRD) project 'Dynamics of Metal/Ceramic Interface Formation.' Low-energy electron microscopy (LEEM) was used to monitor in real time how the metal/ceramic interface between the alloy NiAl and its oxide formed. The interfaces were synthesized by exposing the clean alloy to oxygen at either low or high temperature. During low-temperature exposure, an initially amorphous oxide formed. With annealing, this oxide crystallizes into one type of alumina that has two orientational domains. While the oxide is relatively uniform, it contained pinholes, which coarsened with annealing. In marked contrast, high-temperature exposure directly produced rod-shaped islands of crystalline oxide. These rods were all aligned along the substrate's [001] direction and could be many microns in length. Real-time observations showed that the rods can both grow and shrink by addition and subtraction, respectively, at their ends.
Date: December 1, 2003
Creator: McCarty, Kevin F.
Partner: UNT Libraries Government Documents Department

Development of filler metals for welding of iron aluminide alloys. Final report

Description: Attempts were made to develop a coating formulation for shielded metal arc (SMA) welding electrodes for iron aluminide alloys. Core wires of various compositions were produced by aspiration casting at ORNL and coating formulation development was conducted by Devasco, Inc. It was found that, except for weld deposit compositions containing less than 10 weight % aluminum, all weld deposits exhibited extensive cold cracking and/or porosity. It was concluded that current coating formulation technology limits successful iron aluminide deposits to less than 10 weight % aluminum.
Date: June 29, 1995
Creator: Goodwin, G. M. & Scott, J. L.
Partner: UNT Libraries Government Documents Department

Dynamical x-ray diffraction from an icosahedral Al-Pd-Mn quasicrystal

Description: Primary extinction effects in diffraction from single grains of Al-Pd- Mn, and presumably many other FCI alloys, may be significant and should be corrected for prior to use of diffraction data in structural determinations. Probes based on dynamical diffraction effects, such as x-ray standing wave fluorescence, multiple beam interference, and x-ray transmission topographs, may now be used to study the bulk and surface structure of some quasicrystals. The observation of dynamical diffraction from icosahedral Al-Pd-Mn is a striking confirmation of the fact that quasicrystals can present a degree of structural perfection comparable to that found in the best periodic intermetallic crystals.
Date: April 23, 1996
Creator: Kycia, S.
Partner: UNT Libraries Government Documents Department