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A new discontinuously reinforced aluminum MMC: Al+AlB{sub 2} flakes

Description: Development of a novel metal matrix composite based on the Al-B alloy system has been undertaken. Preparation of this discontinuously reinforced material is based on the precipitation of high aspect ratio AlB{sub 2} from an Al-B alloy. This paper describes a number of efforts forced on preparing high volume fractions (> 30 v%) of AlB{sub 2} in aluminum. New insights into the behavior of the Al-B alloys system allowed this effort to be successful.
Date: June 8, 2000
Partner: UNT Libraries Government Documents Department

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 new active solder for joining electronic components

Description: Electronic components and micro-sensors utilize ceramic substrates, copper and aluminum interconnect and silicon. The joining of these combinations require pre-metallization such that solders with fluxes can wet such combinations of metals and ceramics. The paper will present a new solder alloy that can bond metals, ceramics and composites. The alloy directly wets and bonds in air without the use flux or premetallized layers. The paper will present typical processing steps and joint microstructures in copper, aluminum, aluminum oxide, aluminum nitride, and silicon joints.
Date: May 11, 2000
Partner: UNT Libraries Government Documents Department

Structural influences on the work hardening behavior of aluminum

Description: Effects of various grain and subgrain morphologies on low temperature work hardening of pure Al is studied using tensile tests. Plotting the work hardening rate as a function of true stress, the work hardening is separable into two distinct regimes. Both regimes are approximated by a line {Theta} = {Theta}{sub 0} {minus} K{sub 2}{sigma}, where {Theta}{sub 0} is theoretical work hardening rate at zero stress and K{sub 2} is related to dynamic recovery rate. The first or early deformation regime exhibits greater values of {Theta}{sub 0} and K{sub 2} and can extend up to the first 10% strain of tensile deformation. This early deformation regime is contingent on the existence of a pre-existent dislocation substructure from previous straining. The {Theta}{sub 0} and K{sub 2} associated with the early deformation regime are dependent on the strength and orientation of the pre-existent dislocation substructure relative to the new strain path. At high enough temperatures, this pre-existent dislocation substructure is annealed out, resulting in the near elimination of the early deformation regime. In comparison, the latter regime is dominated by the initial grain and/or subgrain morphology and exhibit lower values of {Theta}{sub 0} and K{sub 2}. The actual value of K{sub 2} in the latter regime is strongly dependent on the existence of a subgrain morphology. Recrystallized or well-annealed microstructures exhibit greater values of K{sub 2} than microstructures that remain partially or fully unrecrystallized. The higher K{sub 2} value is indicative of a more rapid dynamic recovery rate and a greater degree of strain relaxation. The ability to achieve a more relaxed state produces a low-energy cellular dislocation substructure upon deformation. The introduction of subgrains hinders the evolution of a low-energy dislocation cell network, giving way to a more random distribution of the dislocation density.
Date: December 1, 1994
Creator: Chu, D.
Partner: UNT Libraries Government Documents Department

An Experimental Investigation of a Prescription for Identifying Plastic Strain

Description: A series of experiments is described in which a novel prescription for the identification of plastic strain is tested to determine its validity in the context of the strain-space formulation of rate-independent plasticity. Biaxial experiments were performed on several thin-walled aluminum 1100-O cylindrical specimens.
Date: February 29, 2000
Creator: Brown, A.A.; Casey, J. & Nikkel, D.J.
Partner: UNT Libraries Government Documents Department

The use of synthetic hydrocalcite as a chloride-ion getter for a barrier aluminum anodization process

Description: Chloride ion contamination at parts per billion concentrations plaques electrochemists studying barrier anodic aluminum oxide film growth and anodic aluminum oxide capacitor manufacturers. Chloride ion contamination slows film growth and reduces film quality. We have demonstrated that synthetic hydrocalcite substantially reduces the detrimental effects of chloride ion contamination in an aqueous electrolyte commonly used to grow barrier anodic aluminum oxide. We have determined that problems arise if precautions are not taken when using synthetic hydrocalcite as a chloride-ion getter in an aqueous electrolyte. Synthetic hydrocalcite is somewhat hydrophobic. If this powder is added directly to an aqueous electrolyte, some powder disperses; some floats to the top of the bath and forms scum that locally impedes anodic film formation. Commercially available powder contains a wide range of particle sizes including submicrometer-sized particles that can escape through filters into the electrolyte and cause processing problems. These problems can be over come if (1) the getter is placed in filter bags, (2) a piece of filter paper is used to skim trace amounts of getter floating on the top of the bath, (3) dummy runs are performed to scavenge chloride-ion loaded getter micelles dispersed in the bath, and (4) substrates are rinsed with a strong stream of deionized water to remove trace amounts of powder after anodization.
Date: November 1, 1995
Creator: Panitz, J.K.G. & Sharp, D.J.
Partner: UNT Libraries Government Documents Department

Reactive plasma atomization of aluminum nitride powder

Description: Experiments were performed to synthesize AlN powders by reacting Al with N using a conventional dc arc plasma as heat source. Feeding Al powder into Ar/N plasma open to atmosphere produced mainly Al oxide. Experiments using a chamber backfilled with nitrogen suppressed the Al oxide, but little AlN was formed. A furnace and crucible assembly was designed to feed molten Al directly into a DeLaval nozzle attached to the face of the dc arc plasma gun. Resulting submicron powders show a significant increase in AlN formation. This was dependent on chamber pressure, plasma velocity, and molten liquid feed rate. Experimental parameters, equipment design, effects of atomization/vaporization/condensation are discussed.
Date: February 1, 1997
Creator: Prichard, P.; Besser, M.; Sordelet, D. & Anderson, I.
Partner: UNT Libraries Government Documents Department

Interfacial Microstructure Formed by Reactive Metal Penetration of Al into Mullite

Description: Microstructure in the reaction interface between molten Al and dense mullite have been studied by transmission electron microscopy to provide insight into mechanisms for forming ceramic-metal composites by reactive metal penetration. The reactions, which have the overall stoichiometry, 3Al#iz01~ + (8+ x)A1 + 13 AlzO~ + xA1 + 6Si, were carried out at temperatures of 900, 1100, and 1200oC for 5 minutes and 60 minutes, and 1400oC for 15 minutes. Observed phases generally were those given in the above reaction, although their proportions and interracial rnicrostructures differed strongly with reaction temperature. After reaction at 900oC, a thin Al layer separated unreacted mullite from the cx-AlzO~ and Al reaction products. No Si phase was found near the reaction front. After 5 minutes at 1100"C, the nxtction front contained Si, ct-A120~, and an aluminum oxide phase with a high concentration of Si. After 60 minutes at 11O(YC many of the cx-A120g particles were needle-shaped with a preferred orientation. After reaction at 1200oC, the reaction front contained a high density of Si particles that formed a continuous layer over many of the mullite grains. The sample reacted at 140VC for 15 minutes had a dense ct-A120J reaction layer less than 2~m thick. Some isolated Si particles were present between the a-AlzO~ layer and the unreacted mullite. Using previously measured reaction kinetics data, the observed temperature dependence of the interracial microstructure have been modeled as three sequential steps, each one of which is rate-limiting in a different temperature range.
Date: April 27, 1999
Creator: Du, T.B.; Ewsuk, K.G.; Fahrenholtz, W.G.; Loehman, R.E. & Lu, P.
Partner: UNT Libraries Government Documents Department

Generation of Chloride Active Defects at the Aluminum Oxide Surface for the Study of Localized Corrosion Initiation

Description: The generation of surface defects on electron cyclotron resonance (ECR) plasma derived aluminum oxide films has been studied. We find that Cl active O vacancies can be generated using electron and ion irradiation yielding surface concentrations of 3 xl 013 to 1X1014 sites"cm-2. These values correspond to surface defect concentrations of 3 to 10% when compared to ordered, crystalline u-alumina. The vacancies appear to be responsible for increased surface O concentrations when immersed in water. Anodic polarization of irradiated films yields a decrease in the stable pitting potential which correlates with electron dose.
Date: December 7, 1998
Creator: Barbour, J.C.; Missert, N.; Son, K.-A; Wall, F.D. & Zavadil, K.R.
Partner: UNT Libraries Government Documents Department

A method for treating electrolyte to remove Li{sub 2}O

Description: Electrorefining has been used in processes for recovering uranium and plutonium metals from spent nuclear fuel. The electrorefining is performed in an electrochemical cell in which the chopped fuel elements from the reactor forms the anode, the electrolyte, preferably, is the fused eutectic salt of the LiCl-KCl which contain UCl{sub 3} and PuCl{sub 3}. Purified metal collected at the cathode collects at the bottom of the cell. This invention provides a method for removing lithium oxide from the electrolyte salt, with the end formation of a solid lithium-aluminium alloy.
Date: April 1, 1998
Creator: Tomczuk, Z.; Miller, W.E.; Johnson, G.K. & Willit, J.L.
Partner: UNT Libraries Government Documents Department

Measurement of the density of liquid aluminum-319 alloy by an x-ray attenuation technique

Description: This study was made for assisting in casting simulations. A relatively simple apparatus was constructed for measuring the density of Al-based alloys in the solid and liquid states up to 900 C. One of the more important physical properties of a casting alloy, solidification shrinkage, was measured for a commercial Al alloy (Al-319). It was found that while the thermal expansion of Al-319 in both solid and liquid phases is similar to that of pure Al, the density of the liquid alloy is lower than estimated by averaging the atomic volumes of the pure liquid components. The densities were measured by x-ray attenuation.
Date: November 1, 1994
Creator: Smith, P.M. & Gallegos, G.F.
Partner: UNT Libraries Government Documents Department

A molecular dynamics study of the {Sigma}11 <1{bar 1}0>/(113)(133) grain boundary in Al and Al-Cu

Description: We present results of molecular dynamics simulation studies of Cu segregation to the {Sigma}11{l_angle}1{bar 1}0{r_angle}/(113)(113) grain boundary (GB) in Al. Simulations were performed with EAM potentials for Al and Al-Cu. Results predict that Cu atoms tend to order along either side of the interface even in the pure symmetrical tilt boundary, forming alternating chains along the {l_angle}{bar 3}{bar 3}2{r_angle} direction. Nucleation of the chains is driven by a change in the local atomic level stress induced by the pre-existing Cu atoms at the GB.
Date: May 16, 1996
Creator: Huang, H.; Rubia, D. de la & Fluss, M.J.
Partner: UNT Libraries Government Documents Department

On the origin of laser-induced surface activation of ceramics

Description: Pulsed-laser irradiation of Al{sub 2}O{sub 3} and AlN surfaces promotes Cu deposition when the irradiated substgrates are immersed in an electroless bath. In this paper, the nature of the surface modification is analyzed using Auger emission spectroscopy (AES) and cross sectional transmission electron microscopy. During irradiation, AlN thermaly decomposes, leaving a discontinuous metallic film on the surface. A film of Al{sub 2}O{sub 3} is detected at the surface of the irradiated AlN substrate, much thicker when the irradiation is done in an oxidizing atmosphere than in a reducing one. Nanoparticles of metallic Al are generated during laser irradiation of Al{sub 2}O{sub 3} in a reducing atmosphere. When the Al{sub 2}O{sub 3} irradiation is done in an oxidizing atmosphere, regions containing Al or substoichiometric alumina are detected by AES. It is concluded that the presence of metallic Al is the main reason why electroless deposition can occur in both AlN and Al{sub 2}O{sub 3}. Deposition kinetics are consistent with this conclusion. It is likely that also substoichiometric alumina helps to catalyze the electroless deposition.
Date: February 1996
Creator: Pedraza, A. J.; Park, J. W.; Cao, S.; Allen, W. R.; Lowndes, D. H. & Allen, W. R.
Partner: UNT Libraries Government Documents Department

Die Soldering in Aluminium Die Casting

Description: Two types of tests, dipping tests and dip-coating tests were carried out on small steel cylinders using pure aluminum and 380 alloy to investigate the mechanism of die soldering during aluminum die casting. Optical and scanning electron microscopy were used to study the morphology and composition of the phases formed during soldering. A soldering mechanism is postulated based on experimental observations. A soldering critical temperature is postulated at which iron begins to react with aluminum to form an aluminum-rich liquid phase and solid intermetallic compounds. When the temperature at the die surface is higher than this critical temperature, the aluminum-rich phase is liquid and joins the die with the casting during the subsequent solidification. The paper discusses the mechanism of soldering for the case of pure aluminum and 380 alloy casting in a steel mold, the factors that promote soldering, and the strength of the bond formed when soldering occurs. conditions, an aluminum-rich soldering layer may also form over the intermetallic layer. Although a significant amount of research has been conducted on the nature of these intermetallics, little is known about the conditions under which soldering occurs.
Date: March 15, 2000
Creator: Han, Q.; Kenik, E.A. & Viswanathan, S.
Partner: UNT Libraries Government Documents Department

Quantitative assessment of pore development at Al2O3/FeAl interfaces during high temperature oxidation

Description: Alloys of commercial grades that do not contain a reactive element, such as yttrium, often develop pores at the scale/alloy interface. The accumulation and growth of these pores greatly weaken scale adhesion. The purpose of this study is to evaluate pore development in Fe-40at% Al and determine the change in pore volume with oxidation time. Experimental results are then compared to a theoretical calculation where all vacancies are allowed to condense as voids. After removing the oxide scales that formed after various times of oxidation at 1000 C in oxygen, the alloy surface was analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM) to determine the size and depth of interfacial pores. Results are discussed in light of possible mechanisms involved in pore formation at scale/alloy interfaces.
Date: April 24, 2001
Creator: Hou, Peggy Y.; Van Leiden, C.; Niu, Y. & Gesmundo, F.
Partner: UNT Libraries Government Documents Department

Advanced process development for high reflector coatings on solar concentrator panels. Final letter report

Description: Objectives were to develop and demonstrate the manufacturing process for vacuum deposition of low-cost thin-film high reflectance coatings onto large solar concentrator panels; demonstrate thin-film deposition processes for commercialization of this technology by United Solar Technologies (UST); apply reflective coatings to solar concentrator panels for prototype application by UST.
Date: October 1, 1996
Creator: Martin, P.M.; Stewart, C.D.; Bennett, W.D. & Johnston, J.W.
Partner: UNT Libraries Government Documents Department

Investigation of the effect of microstructure on the R-Curve behavior of metal-ceramic composites

Description: An investigation was made into the effect of microstructure on the peak toughness and shape of the crack growth resistance curves for two ceramic-metal composites. An Al{sup 2}O{sup 3}/Al composite formed by Reactive Metal Penetration was used along with an AlN/Al composite formed using a reactive infiltration technique. The results indicate that the toughness increases with an increase in the volume fraction of the metal phase for a particular composite composition, and the peak toughness and shape of the R-Curve also depend on the composite microstructure and metal composition.
Date: July 1, 1995
Creator: Ellerby, D.T.; Flinn, B.D.; Scott, W.D.; Bordia, R.K.; Ewsuk, K.G.; Loehman, R.E. et al.
Partner: UNT Libraries Government Documents Department

Microstructural Characterization of Water-Rich Boehmite (AlO(OH)): TEM Correlation of Apparently Divergent XRD and TGA Results

Description: An understanding of the solid-phase thermodynamics and aqueous speciation of aluminum is critical to our ability to understand and predict processes in a wide variety of geologic and industrial settings. Boehmite (AIO(OH)) is an important phase in the system Al<sub>2</sub>O<sub>3</sub>-H<sub>2</sub>O that has been the subject of a number of structural and thermodynamic studies since its initial synthesis [l] and discovery in nature [2]. Unfortunately, it has long been recognized that thermogravimetric analysis (TGA) of both synthetic and natural boehmite samples (that appear well crystallized by powder XRD methods) yields significant excess water - typically losing 16-16.5 wt. % on heating as compared with a nominal expected weight loss of 15.0 wt. % [3,4]. The boehmite used in our experiments was synthesized hydrothermally from acid-washed gibbsite (Al(OH)<suv>3</sub>) at 200°C. Powder XRD and SEM examination showed no evidence of the presence a contaminant phase. The TGA patterns do not suggest that this is due to adsorbed water, so a structural source is likely. We therefore undertook to examine this material by TEM to clarify this phenomenon.
Date: August 1999
Creator: Allard, L. F.; Anovitz, L. M.; Benezeth, P.; Coffey, D. W.; Palmer, D. A.; Porter, W. D. et al.
Partner: UNT Libraries Government Documents Department

Low-energy deposition of high-strength Al(0) alloys from an ECR plasma

Description: Low-energy deposition of Al(O) alloys from an electron cyclotron resonance (ECR) plasma offers a scaleable method for the synthesis of thick, high-strength Al layers. This work compares alloy layers formed by an ECR-0{sub 2} plasma in conjunction with Al evaporation to 0-implanted Al (ion energies 25-200 keV); and it examines the effects of volume fraction of A1{sub 2}0{sub 3} phase and deposition temperature on the yield stress of the material. TEM showed the Al(O) alloys contain a dense dispersion of small {gamma}-Al{sub 2}0{sub 3} precipitates ({approximately}l nm) in a fine-grain (10-100 nm) fcc Al matrix when deposited at a temperature of {approximately}100C, similar to the microstructure for gigapascal-strength 0-implanted Al. Nanoindentation gave hardnesses for ECR films from 1.1 to 3.2 GPa, and finite-element modeling gave yield stresses up to 1.3 {plus_minus} 0.2 GPa with an elastic modulus of 66 GPa {plus_minus} 6 GPa (similar to pure bulk Al). The yield stress of a polycrystalline pure Al layer was only 0.19 {plus_minus} 0.02 GPa, which was increased to 0.87 {plus_minus} 0.15 GPa by implantation with 5 at. % 0.
Date: December 31, 1995
Creator: Barbour, J.C.; Follstaedt, D.M.; Knapp, J.A.; Myers, S.M.; Marshall, D.A. & Lad, R.J.
Partner: UNT Libraries Government Documents Department