Percent Aluminum Research Articles

Electrochemical Processing of Layered Composite Coatings of Nickel - Aluminum - Alumina / Alumina - Yttria Stabilized Zirconia

ABSTRACTMultilayered coatings of single and dual particle metal matrix composites, with or without ceramic overlayers, have been produced by a novel combination of electrochemical deposition (electroplating and electrophoretic deposition) and reaction bonding. The coatings contain the following layers in a variety of combinations deposited on Ni substrates: (i) electroplated composites of Ni with Al and/or alumina particles, (ii) precursor Al + A12O3 + yttria stabilized ZrO2 transformed into A12O3 + yttria stabilized ZrO2 by the reaction bonding method, and (iii) yttria stabilized ZrO2. In order to determine the appropriate processing parameters for the multilayered coatings, uniform one-layer coatings were deposited and characterized. We find that in the dual particle Ni-Al-Al2O3 coatings the volume percent of the particles does not show a dependence on deposition current density. However, volume percent alumina in these coatings has a strong dependence on the amount of this particle in the plating bath, while the volume percent Al shows only a weak dependence on its bath content. Comparison of the deposition behavior of these dual particle with single particle coatings, containing Al or alumina only, reveals that the presence of Al in the bath interferes with the codeposition of alumina. This interference, however, is not reciprocal. When coatings containing Al are annealed, Ni and Al react to form a solid solution of Al in Ni (γ) or a two phase mixture of this solid solution and the intermetallic, Ni3Al, (γ-γ') depending on the annealing temperature. Finally, we find that the formation of the reaction bonded alumina plus yttria stabilized zirconia layer requires the oxidation resistance afforded by aluminum in the underlying electroplated layer.

High temperature deformation characteristics of Ti(41–52) at% Al alloys

Titanium aluminide alloys of engineering interest contain 46 to 50 atomic percent aluminum and typically up to 20 volume percent of alpha-2 (Ti[sub 3]Al) as a second phase in the gamma (TiAl) matrix. The volume percent and aluminum content of the alpha phase in Ti-48Al vary substantially between 1,200 C and 1,300 C where near-gamma titanium aluminides are usually worked. The microstructures of the alloys in this temperature range consist of a mixture of gamma and disordered alpha. The volume fractions of gamma and disordered alpha present between 1,200 C and 1,300 C have significant effects on high temperature workability of the alloys. Upon cooling to room temperature, the alpha phase transforms to alpha-2 and gamma lamellae, and as a result, the volume percents of the phases present at room temperature are functions of the exact composition of the alloy, the deformation temperature, and cooling rates. The gamma and alpha-2 phase are ordered at room temperature and the relative volume fraction and morphology of each phase have significant effect on the resultant room temperature properties. To optimize both workability and room temperature mechanical properties, a precise knowledge of the effects of alloy composition and varying amounts of gamma and alpha-2more » phases on high temperature deformation is essential. The high temperature deformation characteristics at 1,200--1,300 C and effective strain rates of 10[sup [minus]3]--10[sup [minus]1] s[sup [minus]1] of Ti-xAl (x = 41, 48, 52 at%) alloy were studied with the objective of understanding the deformation of two phase gamma + alpha-2 alloys in terms of the deformation characteristics of individual phases. The goal of this research is to develop a model which describes the deformation behavior of two phase titanium aluminides as a function of constituent phases, test temperature, and strain rate.« less

Room temperature recrystallization of 99.999 pct aluminum

It has been known that recrystallization of metals can be accelerated by a combined effect of high purity and a heavy deformation. There is an increasing interest in deformation and recrystallization behaviors of high purity aluminum, because of the sensitivity of its recrystallization temperature to impurities. Room temperature recrystallization of high purity aluminum is a typical example of this sensitivity and has been found and displayed in an earlier work. This result has been thought to occur statically, because aluminum was only known to undergo dynamic recovery (DRV) as a restoration mechanism due to a high stacking fault energy. However, some recent studies suggested the occurrence of dynamic recrystallization (DRX) in room temperature compression tests of 99.999 pct aluminum. Thus, the restoration mechanism of 99.999 pct aluminum during deformation is in dispute. The purpose of this study is to clarify whether or not DRX can occur in 99.999 pct aluminum that is subjected to plastic deformation at room temperature.

The Electrodeposition of Copper and Nickel in the Acidic Room-Temperature Aluminum Chloride-1-Methyl-3-ethylimidazolium Chloride Molten Salt

The electrodeposition of copper and nickel was investigated at polyciystalline platinum, gold, and tungsten and at glassy carbon electrodes in the acidic 66.7–33.3 mole percent aluminum chloride-1-methyl-3-ethylimidazoIium chloride molten salt. The electrodeposition of these metals at platinum and gold is complicated by underpotential deposition phenomena whereas the electrodeposition of these metals at glassy carbon and tungsten requires a significant nucleation overpotential. Dimensionless experimental current-time transients recorded at glassy carbon and tungsten are in good agreement with theoretical models based on three-dimensional nucleation with diffusion-controlled growth of the nuclei. The reduction of nickel(II) on nickel in this molten salt appears to involve the concurrent formation of a soluble nickel species.

Fabrication of metal matrix composites of TiC-Al through Self-Propagating Synthesis Reaction

Fine fibrous titanium carbide (TiC) was processed through the self-propagating high-temperature synthesis (SHS) method and employed to fabricate aluminum matrix composites. Two consol-idation methods were investigated: (1) combustion synthesis of TiC fiber/Al composites directly using titanium powders and carbon fibers ignited simultaneously with varying amounts of the matrix metal powder and (2) combustion synthesis of TiC using titanium powders and carbon fibers followed by consolidation into different amounts of the metal matrix powder, Al,via hot isostatic pressing (HIP). In the former method, when the amount of the Al in the matrix was increased, the maximum temperature obtained by the combustion reaction decreased and the propagation of the synthesis reactions became difficult to maintain. Preheating was required for the mixture of reactants with more than approximately 5 mole pct aluminum matrix powders in order to ignite and maintain the propagation rate. Microstructural analysis of the products from the Al/C/Ti reaction without preheating shows that small amounts of an aluminum carbide phase (AI4C3) are present. In the second method, following separation of the individual fibers in the TiC product, dense composites containing the SHS products were obtained by HIP of a mixture of the TiC fibers and Al powders. No ternary phase was formed during this procedure.

Prevention of the intergranular fracture by addition of silicon and aluminum to a high-purity Fe-0.2 Pct P alloy with a trace of boron

The effect of addition of 0.25 pct silicon and aluminum on the intergranular fracture and the grain-boundary segregation of solutes in a high-purity Fe-0.2 pct P alloy with a trace of boron has been investigated by impact test, tensile test at low temperatures, optical and scanning electron microscopy, and Auger electron spectroscopy (AES). The addition of 0.25 pct silicon and aluminum remarkably reduces the susceptibility of an Fe-0.2 pct P alloy to the intergranular fracture and decreases the ductile-brittle transition temperature (DBTT). The addition of silicon and aluminum causes considerable segregation of boron to grain boundaries and, simulta-neously, remarkably decreases the segregation of phosphorus in the Fe-0.2 pct P alloy. The cause for these effects is discussed.

A statistical approach to the heat treatment optimization of Al-Al2O3 particulate composites

The effects of three heat treatment variables—solutionizing time, aging time, and aging temperature—on the yield and ultimate tensile strength of alumina/aluminum metal matrix composites were studied using a statistical technique known as the Taguchi Method. Composites consisting of 10,15, and 20 volume percent alumina particulate reinforcements in a 6061 alloy matrix were investigated. Fractional factorial experimentation was performed using three levels for volume percentage of reinforcement and the three heat treatment parameters. Based on the Taguchi analysis, the optimal combination of heat treatment variables for each reinforcement volume percentage of these alumina/aluminum composites consists of 6 hours (instead of the standard 2 hours) of solutionizing at 985 °F (529 °C) followed by aging at 320 °F (160 °C). The predicted optimal strength correlated very closely to actual results obtained during experimentation. SEM micrographs illustrate the microstructural differences that occur as a result of the various combinations of heat treatment.

Repassivation of Rapidly Solidified Magnesium‐Aluminum Alloys

Electrochemical techniques and electron microscopy were used to investigate the effects of rapid solidification processing (RSP) and aluminum content on the repassivation of binary magnesium‐aluminum alloys in aqueous solutions of potassium chromate and sodium chloride (pH 9.1). This electrolyte resembles environments causing pitting corrosion and stress corrosion cracking in Mg‐Al alloys, where chromate ions, applied as a corrosion protection measure, coexist with chloride ions indigenous to sea water and other natural electrolytes. Macrocrystalline alloys containing 1 and 9 weight percent (w/o) aluminum were prepared using a melt‐spinning process which yields continuous ribbons 15–25 μm thick. Ribbon microstructures were characterized using optical and transmission electron microscopy. Breakdown of passivity was initiated by a potential pulse or physical scratch, and repassivation was then evaluated using transient current measurements and scanning electron microscopy. The rapidly solidified alloys experienced relatively uniform attack, and repassivated faster and more completely than their as‐cast counterparts. In both the as‐cast and RSP conditions, increasing the aluminum content improved the repassivation rate in chromate/chloride solution of Mg‐Al alloys containing 1 and 9 w/o Al.

Delayed failure of PH13-8Mo steel plated with AI-IVD

We have experienced failure of the bolts for aircraft made of PH13-8Mo steel. The failure occurred a short time after the bolts had been fastened for assembly of aircraft parts. These bolts had been aluminum plated with ion vapor deposition (IVD) process. Based on this trouble, delayed failure of PH13-8Mo steel plated with aluminum by IVD was studied to clarify the cause of the trouble. Sustained load tests were performed in distilled water with notched specimens made of PH13-8Mo steel on which aluminum was plated by the same IVD process as defective bolts. From the tests carried out on many heats of PH13-8Mo steel, aged at 783 K (510°C), the following results were obtained: (1) heats containing more than 1.16 pct aluminum exhibited premature delayed failure with a low stress level threshold; (2) the heats containing less than 0.025 pct carbon and less than 1.16 pct aluminum showed extensive scatter in the values of threshold stress; and (3) the heats containing more than 0.025 pct carbon and less than 1.16 pct aluminum did not exhibit the premature delayed failure even at high stress levels. From the measurement of electrical resistivity changes associated with isothermal aging of PH13-8Mo steel, it is evident that the low-temperature phase formed by aging plays an important role in delayed failure and formation of the phase is significantly influenced by carbon and aluminum contents in the steel. Microcracks were found to form on the aluminum film plated by IVD when stress was applied to the specimen. Therefore, a galvanic couple would be constructed between coated aluminum and PH13-8Mo steel with the presence of distilled water which penetrated through the cracks initiated when the load was applied to the specimen. Hydrogen necessary to give rise to the delayed failure is produced by the cathodically polarized condition. Notch toughness was also controlled by carbon and aluminum contents in PH13-8Mo steel; however, it is not thought that the decrease in notch toughness plays a significant role in the cause of delayed failure. It is particularly noteworthy that carbon in the steel is useful to prevent the delayed failure and to keep excellent notch toughness in PH13-8Mo steel aged to high strength levels.

Effect of reinforcement on the aging response of cast 6061 Al-Al2O3 particulate composites

The effect of 10 and 15 vol pct alumina particulate addition on the age hardening behavior of cast 6061 Al-matrix composites was studied using microhardness, electrical resistivity, differential scanning calorimetry, and transmission electron microscopy (TEM). It was found that the kinetics of precipitation in the matrix alloy are significantly accelerated due to the presence of reinforcements. This acceleration is attributable to the decrease in incubation time required for nucleation and the increase in solute diffusivity and hence precipitate growth rate resulting from the increase in the matrix dislocation density due to coefficient of thermal expansion (CTE) mismatch between the matrix and the reinforcements. The relative amounts of the various phases were also observed to be affected by reinforcement addition. Increasing reinforcement content decreased the volume fractions of the Β’ and Β precipitates while increasing the volume fraction of the GP-I zones. The volume fraction of silicon clusters (which are the precursors to GP zones in 6061 Al) formed during postsolution treatment aging was found to decrease with increasing reinforcement addition. The above effects have been discussed with respect to the associated mechanisms, and plausible explanations have been offered.

Phonon dispersion curves for ordered, partially-ordered and disordered iron-aluminium alloys

Neutron inelastic scattering determination of the phonon dispersion curves in high symmetry directions for iron-aluminium alloys are presented. The alloys have compositions near 25 atomic percent aluminium, and were prepared in three states of ordered BCC, B2 and D03 structures. The data were analysed by fitting sixth-nearest neighbour Born-von Karman models. The phonon frequencies follow a consistent trend in the ordering sequence BCC to B2 to D03. A similar trend is apparent in the values of the atomic force constants for the nearest neighbours but is less apparent for the force constants for more distant neighbours. Of the low frequency modes, the soft (qq0) transverse mode is the most sensitive to changes in the atomic force constants. High frequency modes exhibit large changes in frequency as a result of ordering because of the large difference in the masses of iron and aluminium atoms, as well as the changes in force constants.

Carbon resistor gauges for measuring shock and detonation pressures. II. Detonation pressure of carbohydrate-metal composite explosives

An estimate of the detonation pressure of carbohydrate-metal composite explosives has been obtained experimentally by use of carbon resistor pressure gauges mounted in the wall of the confining tubes. The composite explosives were formulated from a pharmaceutical mixture of 10/90 nitroglyccrin/ß-lactose by weight, and was rendered detonable by inclusion of flaked aluminum and both flaked aluminum and ammonium perchlorate. The detonation pressure of the nitroglyccrin/ß-lactose mixture with 10 percent aluminum by weight was approximatcly 1.1 GPa. The incorporation of 30 percent ball-milled ammonium perchlorate to this formnlation increased the detonation pressure to 12.2 GPa. These pressures must be considered as estimates of the true detonation pressure, because of (a) the suspected non-ideality of the detonation state of these explosives, (b) the statistical nature of the response of the gauges, and (c) possible inconsistencies in the interpreatation of the gauge records. It is recommended that a number of gauges be used in a given experiment, and the results be averaged as one means of cireumventing the above difficulties.

Electrodissolution and Electrodeposition of Lead in an Acidic Room Temperature Chloroaluminate Molten Salt

The electrodissolution of a lead rotating disk electrode and the electrodeposition and stripping of lead at a glassy carbon electrode were studied in the 66.7‐33.3 mole percent (m/o) aluminum chloride‐1‐methyl‐3‐ethylimidazolium chloride molten salt at 40°C. The electrodissolution of lead to produce lead(II) is a quasireversible process with an anodic transfer coefficient and a formal heterogeneous rate constant of and , respectively. The electrodeposition of lead on glassy carbon from solutions of exhibits progressive three‐dimensional nucleation with diffusion‐controlled growth of the nuclei. The stripping of lead from this electrode proceeds with 100% efficiency. The formal potential of the Pb2+/Pb couple is , and the diffusion coefficient and Stokes‐Einstein product for lead(II) are and .

Rapid bioassay of aluminum toxicity in soil

Fifty-five acid soil horizons from 19 profiles were evaluated for aluminum toxicity using root elongation as a criterion in a two-day petri dish bioassay. The method proved to be simple, efficient, and precise enough to clearly distinguish aluminum toxicity differences among horizons within and between profiles. Although toxicity patterns within profiles differed, it was common for surface horizons to be less toxic even when very acid. The R2 for correlations of relative root lengths with pH in H2O, pH in KCl, soluble and exchangeable aluminum and percent aluminum saturation were only 0.42, 0.45, 0.52, 0.66, and 0.54, respectively, which indicates the need for a bioassay. In a further use of the method, and to demonstrate its efficiency, 243 horizons from 26 profiles were screened. Approximately half of the horizons with a pH of 5.0 or below showed Al toxicity. When used by different operators, with a variety of soil and treatment parameter changes, the two-day bioassay in petri dishes gave consistent rankings of soils by degree of aluminum toxicity.

The high temperature creep deformation of Si3N4-6Y2O3-2Al2O3

The creep properties of silicon nitride containing 6 wt percent yttria and 2 wt percent alumina have been determined in the temperature range 1573 to 1673 K. The stress exponent, n, in the equation epsilon dot varies as sigma sup n, was determined to be 2.00 + or - 0.15 and the true activation energy was found to be 692 + or - 25 kJ/mol. Transmission electron microscopy studies showed that deformation occurred in the grain boundary glassy phase accompanied by microcrack formation and cavitation. The steady state creep results are consistent with a diffusion controlled creep mechanism involving nitrogen diffusion through the grain boundary glassy phase.

Infiltration of fibrous preforms by a pure metal: Part II. Experiment

In a previous paper, a theory was developed to describe the flow of a pure metal into a fibrous preform. This paper presents experimental data to test the results of the theory for pure aluminum flowing into fibrous alumina preforms. An apparatus was designed and built for unidirectional infiltration under constant pressure and carefully controlled temperature parameters. A sensor was also developed to measure the position of the liquid metal in the fibrous preform during the experiment. This technique enabled quantitative comparison of theory and experiment. Experimental data are reported for the infiltration by 99.999 and 99.9 wt pct pure aluminum of SAFFIL alumina fibers fabricated into two-dimensionally random preforms. Fiber volume fraction was varied from 0.22 to 0.26, fiber preheat temperature was varied from approximately 483 to 743 K, and metal superheat was varied from 20 to 185 K. Infiltration pressure was varied from 1 to 4.5. MPa (145 to 650 psi). Agreement between theory and experiment was very good under all the experimental conditions studied for the 99.999 wt pct pure matrix. The impurity level of the metal was found to influence infiltration significantly. The measured perform permeability for 99.9 wt pct aluminum was much lower than that for 99.999 wt pct aluminum.

ChemInform Abstract: Synthesis and Properties of Metallic Glasses that Contain Aluminum.

The synthesis and properties of a class of metallic glasses containing up to 90 atomic percent aluminum are reported. The unusual formability of the glasses and their structural features are pointed out. Mechanical properties including tensile fracture strength and Young's modulus are reported along with crystallization temperatures. The unusually high strengths of the aluminum glasses can be of significant importance in obtaining high-strength low-density materials.

Synthesis and Properties of Metallic Glasses That Contain Aluminum

The synthesis and properties of a class of metallic glasses containing up to 90 atomic percent aluminum are reported. The unusual formability of the glasses and their structural features are pointed out. Mechanical properties including tensile fracture strength and Young's modulus are reported along with crystallization temperatures. The unusually high strengths of the aluminum glasses can be of significant importance in obtaining high-strength low-density materials.

Effect of Land Clearing Method on Chemical Properties of an Ultisol In the Amazon

AbstractThis study quantified soil chemical properties as affected by land clearing method and subsequent soil management. It was conducted on a Yurimaguas soil (fine‐loamy, siliceous, isohyperthermic Typic Paleudults) covered by a 20‐yr‐old evergreen forest in the Amazon Basin of Peru. The experimental design, a split plot replicated three times, included six main plot treatments: (i) slash and burn clearing; (ii) bulldozer clearing with a straight blade; (iii) straight blade clearing followed by chisel plowing 25 cm deep; (iv) bulldozer clearing with shear blade, vegetation burned, followed by disking 30 cm deep; (v) shear blade clearing and rototilling with a 10‐KW tractor; and (vi) shear blade clearing, 30‐cm‐deep disking, followed by rototilling. Three post clearing soil management practices (subplots) were: (1) flat planted with no fertilizer or lime; (2) flat planted with fertilizer and lime applications incorporated, based on soil test recommendations; and (3) soil bedded at 1.1‐m spacings, and fertilizer and lime applied as in Subplot 2. Five successive crops, rice (Oryza sativa L.)‐soybean [Glycine max (L.) Merr.]‐corn (Zea mays L.)‐rice‐corn were grown from July 1980 to July 1982. Soil samples collected before or just after harvest of the first, second, and third crops were analyzed for chemical properties. Burning dried vegetation resulted in higher concentrations of Ca, Mg, P, and K in the 0‐ to 45‐cm soil layer. No significant differences due to main treatments were found for the other chemical properties. The pH of the surface soil increased from 4.0 to 5.2 for all limed subplots. Percent aluminum saturation decreased from 82 to 7%, and P, Ca, Mg, and effective cation capacity increased. The decrease in topsoil organic carbon at 14 wk for all mechanically cleared treatments was probably due to increased oxidation rates due to tillage and higher soil temperatures. Concentrations of Cu, Fe, and Mn in the soil were unaffected by treatment.

Erosion of fiber reinforced Ai-4 pet CU composites

Erosion tests were carried out on a series of Al-4 pct Cu metal matrix composites containing up to 30 vol pct alumina fibers. The erosion rates were found to increase significantly with increasing fiber content. Analysis of the shift of low-angle impact erosion rate data suggests that increasing fiber content imposes ductility constraints for the deformation mechanisms operative during the erosion and impact process. SEM observations on eroded surfaces support this view. Tensile tests on the same materials also showed strong ductility constraints as a result of fiber additions. The erosion rates could be correlated inversely with the parameter σm ef obtained from tensile tests where σem is the maximum stress in the sample before failure and ef is strain to fracture. Hardness alone was not a suitable parameter for correlation because erosion rates increased with increasing hardness, contrary to what is expected based on existing theories that use hardness as the single materials parameter to model erosion.