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The addition of lithium to high strength aluminum alloys significantly improves specific strength as is the case with AA 2195. However, unlike non-lithium containing alloys, such as AA 7075, lithium containing alloys display anisotropic mechanical properties in low aspect ratio extruded sections. The goal of this study is to elucidate the origins of anisotropy in AA 2195 and to investigate processing methods to control mechanical properties. To this end, both AA 2195 and AA 7075 were systematically extruded over a range of aspect ratios from 2 to 15 while maintaining a constant extrusion ratio. Through crystallographic texture component analysis and the use of a newly proposed parameter termed the “Plate-Like Number”, this study indicates that the Copper texture is primarily responsible for previously observed anisotropic properties of AA 2195. A series of rolling studies analyzed using the Plate-Like Number suggest that a higher initial billet temperature will minimize the Copper texture component and thus reduce the anisotropy in extruded AA 2195.

The dynamic yielding and tensile fracture (spalling) behavior of an annealed aluminum–magnesium alloy is investigated using symmetric plate impact experiments. The Hugoniot elastic limit displays upper and lower yield points, with the lower yield point remaining constant near 0.33 GPa and the upper yield point increasing from 0.38 to 0.48 GPa with increasing peak stress. The dynamic fracture (spall) strength also increases with peak stress from 0.84 to 0.92 GPa.

Investigations of the production of thin-walled steel alloys through the gas carburization of structures made from reduced and sintered metal oxide powders were performed. Extrusions with low-alloy steel composition were produced successfully without the occurrence of metal dusting, yielding a novel technique for the production of thin-walled steel structures. Thin strip geometries (~200 to 300 μm final thickness) of samples with the composition of 4140 steel, without carbon, were produced through the extrusion of a paste of metal-oxide powders. Full reduction and sintering in a 10 pct H2/90 pct Ar atmosphere yielded a metal part containing all necessary alloying elements except carbon. Gas carburization in a controlled CO/CO2 atmosphere was then used to introduce carbon through the thickness of the structure while carburization parameters were controlled such that metal dusting was not observed. It has been shown in this study, through heat treatment and microstructural investigations, that structures with 4140 composition displaying microstructures and mechanical properties comparable with conventionally made steels can be reached in approximately 30 minutes during gas carburization. The research shows that carbon contents above the eutectoid composition can be reached in less than 30 minutes. As a result, a novel alloy development tool has been introduced.

Zirconium diboride and a zirconium diboride/tantalum diboride mixture were synthesized by solution-based processing. Zirconium n-propoxide was refluxed with 2,4-pentanedione to form zirconium diketonate. This compound hydrolyzed in a controllable fashion to form a zirconia precursor. Boria and carbon precursors were formed via solution additions of phenolformaldehyde and boric acid, respectively. Tantalum oxide precursors were formed similarly as zirconia precursors, in which tantalum ethoxide was used. Solutions were concentrated, dried, pyrolyzed (800°-1100°C, 2 h, flowing argon), and exposed to carbothermal reduction heat treatments (1150°-1800°C, 2 h, flowing argon). Spherical particles of 200-600 nm for pure ZrB 2 and ZrB 2 -TaB 2 mixtures were formed.

Potential interconnect alloys of Fe–Cr and Fe–Ni–Cr were fabricated via extrusion of metal oxide pastes followed by heat treatment in hydrogen. Thermal expansion of the different alloys was measured and compared with that of yttria-stabilized zirconia (YSZ). Oxidation experiments were performed in air at 700 °C using cyclic heating and weighing, as well as thermogravimetric analysis. Additions of chromium to a Fe50Ni alloy were found to improve oxidation resistance although the performance of Fe–Ni–Cr compositions was inferior to Fe–Cr alloys of similar chromium content. The improvement in oxidation behavior with increasing chromium content of the Fe–Ni–Cr alloys was contrasted with the negative impact of the chromium addition on thermal expansion matching with YSZ. Binary Fe–Cr alloys such as Fe20Cr appear to be better suited for use as a SOFC interconnect compared with Fe42.5Ni15Cr and other similar Fe–Ni–Cr alloys.

The metastable liquidi in the Al–In, Al–Bi, and Al–Pb systems were assessed through the thermodynamic modelling of the liquid miscibility gaps. The subregular solution model was applied to describe the Gibbs free energy of liquid phases and the interaction parameters were optimized using the phase diagram data. In addition, spinodal curves were assessed to predict the possible regions for metastable phases. The present results were compared and discussed with other experimental and assessed data available from the literature.

The microstructure of most as-cast superalloys is highly anisotropic and inhomogeneous. In precipitation hardenable materials it is desirable to know the precipitate dissolution temperature to homogenize the microstructure and tailor the size and distribution of the precipitates to obtain the optimal material properties. Differential thermal analysis, heat treatments followed by microstructural characterization and a dilatometry technique were used to determine the dissolution temperature of the precipitate phase. The values obtained for the dissolution temperature from the three methods are all in agreement and indicate that the dissolution temperature for a nominal superalloy is approximately 1200 °C.

A method for the rapid fabrication of homogeneous potential interconnect alloys from metal oxide precursors and evaluation of their thermal expansion mismatch to solid oxide fuel cells is described. Pastes of metal oxide powders were extruded into honeycomb geometries and sintered in hydrogen. Thermal expansion mismatch was evaluated based on heating with a zero-mismatch at room temperature, and on cooling with zero-mismatch temperatures at 600 or 1100∘C. The non-linear expansion behavior of Fe-Ni invar alloys resulted in different compositions being optimum, based on the assumed zero-mismatch temperature.

The goal of this study is to develop practices for evaluating and predicting the microstructural evolution of directly reduced iron-chromium alloys. This fundamental knowledge is being applied to a process developed at the Georgia Institute of Technology to fabricate metal honeycomb extrusions. A paste composed of oxide powders, binders and lubricants is extruded through a die of the desired cross-section and subsequently reduced to metal with hydrogen. The effects of time, temperature and composition on the extent of reduction and diffusion in reducing Fe2O3-Cr2O3 powder mixtures is investigated. The thermodynamics and kinetics of Fe2O3-Cr2O3 reduction are evaluated in terms of the free energy of formation as well as reducing species. The kinetics of the microstructural changes are evaluated through diffusion measurements. A thermodynamic model for Fe2O3-Cr2O3 was developed and used to determine the maximum amount of Cr2O3 that would reduce when in contact with iron as a function of the $\frac{P_{H_{2}}}{P_{H_{2}O}}$ ratio . Diffusion studies consisted of Fe-Cr2O3 couples held at temperature in a reducing atmosphere. Cr diffusion in Fe showed a concentration dependence for the geometries investigated.

Extrusion of oxide powders allows fabrication of thin-walled metal articles to produce controlled-geometry, low-density copper alloy architectures. Shapes formed with copper oxide powders mixed wit...

Minor additions of Sc are effective in controlling the recrystallization resistance of 5xxx, 2xxx, and 7xxx aluminum. The addition of Sc to aluminum results in the rapid precipitation of homogeneously distributed Al3Sc dispersoids, which are coherent with the matrix and have the L12 structure. The presence of Al3Sc dispersoids increases the recrystallization resistance of wrought alloys. The higher coarsening rate of Al3Sc compared to that of Al3Zr may limit its applications as a single ancillary addition. When both scandium and zirconium are used in the same alloy, Al3(Sc1-x , Zr x ) dispersoids form. These dispersoids are more effective recrystallization inhibitors than either Al3Sc or Al3Zr. The Al3(Sc1-x , Zr x ) dispersoids precipitate more rapidly than Al3Zr but have a slower coarsening rate than Al3Sc. Furthermore, the distribution of Al3(Sc1-x , Zr x ) is significantly more homogeneous than Al3Zr. It was also established that alloys containing up to 3.5Mg showed improvement in recrystallization resistance when both Sc and Zr were present. Several morphologies of Al3Sc and Al3(Sc1-x , Zr x ) were also observed.

H2 reduction and densification of extruded Fe2O3–Cr2O3 mixtures with honeycomb geometry (0.3-mm wall thickness) were studied using dilatometry, x-ray diffraction, and scanning electron microscopy. Reduction of pure Fe2O3 heated at 5 °C/min was completed by approximately 525 °C. Two separate sintering steps ensued, well separated in temperature from reduction, one associated with elimination of pores between Fe agglomerates (750–900 °C), and the other associated with sintering of these agglomerates (995–1275 °C). With increasing Cr2O3 content, sintering was increasingly delayed until initiation of Cr2O3 reduction above 1000 °C. The α → γ iron phase transformations were consistent with the Fe–Cr phase diagram, but the γ → α transformations at higher temperatures deviated from the phase diagram because of the influence of impurities (Si, Ca) in the solid solution. Pure Cr2O3 honeycomb formed an approximately 35-μm-thick porous Cr coating that imposed a diffusion barrier to further reduction. The high vapor pressure of chromium prohibited compositions in excess of 25 wt.% Cr2O3 from full reduction and densification.

A range of compositions and temperatures below the monotectic temperature exists where there are thermodynamic restrictions that prevent the equilibrium solid from forming directly from the undercooled homogeneous liquid. In this region the solid can form only after liquid–liquid phase separation has occurred. As suggested by earlier research, the thermodynamic restrictions on the crystallization process may be useful to control the crystallized grain structure in glass–ceramic systems. Thus, understanding the thermodynamic limitations on the formation of the solid in monotectic systems could have commercial significance. In the present paper, the metastable liquidus boundaries, liquid miscibility gaps, and spinodal curves in the binary La2O3–SiO2, Sm2O3–SiO2, Dy2O3–SiO2, and Er2O3–SiO2 systems were calculated using analytical expressions for the Gibbs free energies of the liquid phases.

A range of compositions and temperatures below the monotectic temperature exists where there are thermodynamic restrictions that prevent the equilibrium solid from forming directly from the undercooled homogeneous liquid. In this region, the solid can form only after liquid-liquid phase separation has occurred. As suggested by earlier research, the thermodynamic restrictions on the crystallization process may be useful to control the crystallized grain structure in glass-ceramic systems. Thus, understanding the thermodynamic limitations on the formation of the solid in monotectic systems could have commercial significance. In the present paper, the metastable liquidus boundaries, liquid miscibility gaps, and spinodal curves in binary MgO-SiO2, CaO-SiO2, and SrO-SiO2 systems are calculated by using analytical expressions for the Gibbs free energies of the liquid phases. Calculating the metastable liquidus rather than using a simple extrapolation as originally proposed in the aforementioned previous research provides greater control of the heat-treatment processes and, thus, greater control over the resulting microstructure.

In most commercial operations, the plant metallurgist likely has little control over the solidification rate of the process. However, solidification rate is affected by the dimensions of the ingot, and product form (plate ingot vs extrusion billet, for example) determines the dimensions of the ingot to be cast. Consequently, understanding the effects of solidification rate might be useful in explaining differences in microstructure that are often observed in various product forms cast from equivalent compositions. To provide this microstructural information, the effect of cooling rate from the melt on the microstructural changes in hot-rolled and solution heat treated (SHT) aluminum alloy 6013 was investigated. The range of cooling rates in this investigation is comparable to what might be observed through the thickness of a plate ingot. Over the cooling rate range investigated (0.5 to 5 K/s), recrystallization behavior of the alloy appears to be primarily affected by the size and number density of the coarse α(AlFeMnSi) constituent particles, which act as sites for particle stimulated nucleation (PSN) of recrystallized grains. At intermediate cooling rates (1.5 K/s), the resistance to recrystallization is at a minimum. As the cooling rate increases beyond 1.5 K/s, the number of particles available for PSN decreases; thus, there is a decrease in the fraction of recrystallized grains after heat treating. On the other hand, as the cooling rate is decreased from 1.5 K/s, the size of the constituents increases; however, their number decreases, once again leading to a decrease in the fraction of recrystallized grains observed after heat treatment.

Employing a distinct variation of the physical vapour deposition technique, lithium vapour has been used to form Mg-Li alloy films whose physical structure can be modified through substrate temperature control over a considerable composition range. In addition to these Mg-Li alloy films, alloys of aluminium and copper can be prepared and modified primarily by controlling the interaction of lithium vapour with the precursor metal in the form of a cast sheet ranging in thickness from 0.02 to 0.07 in. A lithium-mediated process is found to produce a significant vaporization enhancement from the surface of the magnesium sheet at temperatures close to 200°C below that required for vaporization in the absence of lithium. The interaction process not only promotes the vaporization of the magnesium but also leads to an intimate mixing of magnesium and lithium vapours. The lithium and magnesium contents of the formed vapours have been varied to produce alloy films of between 0.08 and 30wt%Li. As the vapour...

The influence of manganese and iron additions on the recrystallization behavior of a hot-rolled Al-Mg-Si-Cu alloy has been investigated. In the as-cast ingot, some manganese remains in supersaturated solid solution and, during the preheating step, precipitates as fine (0.1 to 0.3 μm) dispersoidsα- Al12Mn3Si and α(AlFeMnSi), depending on the local iron content. The presence of the dispersoids increases the alloy’s resistance to recrystallization. The remaining manganese along with iron forms coarse (30 to 100 μm) α(AlFeMnSi) phases in the interdendritic channels upon solidification. During rolling, these coarse phases are broken up and the matrix surrounding the phases is highly strained. The highly strained regions around the precipitates are preferential sites for the nucleation and growth of new, strain-free, recrystallized grains. Decreasing the iron content decreases the amount of coarse α(AlFeMnSi) constituent phase and increases the recrystallization resistance of the alloy for a given concentration of manganese. For iron-free alloys, coarse α-Al12Mn3Si phase forms during solidification. The increased recrystallization resistance is attributed to the lower probability for particle-stimulated recrystallization. Increasing the manganese content beyond what is normally found in 6013 increases the volume fraction of both the dispersoids and the coarse constituent phases. However, the increased volume fraction of the dispersoids in the iron-containing alloys more than compensates for the increase in volume fraction of coarse constituent particles, resulting in an increase in the recrystallization resistance with increased manganese content. In this research, alloys containing varying amounts of manganese and iron with levels of magnesium, silicon, and copper consistent with the nominal composition of 6013 were hot deformed and solution heat treated to produce microstructures ranging from fully recrystallized to unrecrystallized.

In 1988 and 1990, irrigated plots of Florunner peanuts were harvested at weekly intervals to examine the progression of crop maturity profile, maturity distribution in commercial sizes, single seed roast color distribution, and descriptive flavor. Samples were collected 3 wk before through 2 wk after the optimum harvest date predicted by the hull scrape maturity method. Data from these samples indicated consisent pod maturity progression as well as increasingly higher percentages of mature peanuts in each commercial size through optimum harvest date. In 1990, the total percentage of seed from black and brown hull scrape classified pods in the medium commercial size progressed from ca. 48% at 3 wk before optimum to ca. 89% at the optimum harvest date. Distributions of roasted colors of 100 single, medium grade size seed contained fewer dark colored seed with progressive harvest date, and earlier harvests produced darker roasted peanut paste. Mean color of single seed roast color distributions increased (became lighter) in progressive harvest dates and were 3 to 6 Hunter L units higher than the corresponding paste colors. Descriptive roast flavor analysis of paste made from medium-size peanuts harvested in 1990 indicated that, in the earlier harvests, intensities of the descriptors roasted peanutty and sweet aromatic were significantly lower and intensities of dark roast and bitter taste were higher.

The dynamic yielding and fracture (spalling) of commercially pure (grade 4) titanium are investigated using symmetric plate impact experiments for a peak stress range of 5.6 GPa–12.5 GPa. Velocity interferometry system for any reflector rear free surface velocity profiles display both a Hugoniot elastic limit (HEL) and a velocity pullback, which are indicative of dynamic compressive yielding and tensile fracture (spalling), respectively. The HEL decreases with peak stress from 2.2 GPa for 5.6 GPa peak stress to 2.0 GPa for 12.5 GPa peak stress. The decrease in the HEL corresponded to an increase in twinning observed in recovered samples. The spall strength increases with peak stress from 3.3 GPa to 3.8 GPa over the measured peak stress range and shows a good power law fit with the decompression strain rate. The differences in the dynamic yield and fracture behavior indicate that void nucleation is the dominant mechanism affecting the spall strength of grade 4 titanium.

We report a transmission electron microscopy study of α-(Al-Mn-Fe-Si) phases, isostructural to the α-(Al-Mn-Si) approximant phase. Selected-area diffraction patterns exhibit a noticeable diffuse scattering due to short-range ordering. We show that the ordering effect is reinforced by the Mn additions. This diffuse scattering can be described by a surface close to a polyhedron in the reciprocal space. We interpret the shape of this surface as a consequence of the ordering of two types of entities (Mackay icosahedra) along the (111) directions.

Fatigue crack growth (FCG) experiments were conducted on controlled variations of Type 7075 and 7050 aluminum alloys. Alloy FCG resistance was ranked under constant amplitude and simple variable amplitude load spectra. Fracture mechanics and fractographic approaches were used to interpret causes for variation in ranking of 7XXX aluminum alloy FCG resistance with loading conditions. The interpretation is built around clarification of a controlling FCG mechanism that is dependent upon interaction of microstructure and load history. This clarification represents a necessary first step toward knowing which microstructure or which design (test) procedure is optimum for a particular class of application, for example, fighter as opposed to bomber or transport aircraft.

A thermodynamic modeling of phase diagrams in binary alkali silicate systems is described by using the Gibbs free energy of the phases. Simple models employing regular, quasi-regular, and subregular solution models were applied to describe the liquid phase. The interaction parameters of the liquid phases were obtained by using the liquidus curves of silica (and subliquidus data) through a multiple linear regression method. The present calculated liquidus curves agree very well with Cs2O—SiO2 and Rb2O—SiO2 systems. In the K2O—, Na2O—, and Li2O—SiO2 systems, the calculations permitted discrimination between sets of data and, based upon the calculation choices, could be correctly made to select the most appropriate phase diagram. Also, the spinodals were calculated where phase separation can occur by a spinodal decomposition process.

In-shell peanuts stored in large bulk warehouses for short terms may lose approximately 1.5-2% of their value. However, peanuts stored as long as nine months may lose as much as 5% of their value due to excessive moisture loss, reduction of peanut kernel size and damage due to insects or microbial growth Tests were conducted in 2006 and 2007 by placing six woven polypropylene totes, each filled with approximately 500 kg of in-shell peanuts, in a hermetic storage bag. Oxygen level was monitored periodically using a hand-held air sampling unit and oxygen sensor. Temperature was monitored in each tote throughout storage. During the 2006 storage season, oxygen levels reached a minimum of 11% and were higher than the 5% or less reported in storage of other commodities. This was due to the low initial peanut moisture content of 6% and minimal insect infestation. Wet, germinated peanuts were observed in the top of each tote probably due to moisture migration. No detectable change in the mass of peanuts was observed during storage. Seed viability was excellent following storage as indicated by an average 96% germination. During the 2207 storage season, oxygen levels decreased to less than 5% in approximately 10 d, due to increased respiration and mold growth caused by higher initial moisture content. The peanut value decreased an average of 11% during storage. Germination data were not obtained for the 2007 crop peanuts stored due to the excessive mold growth during storage. Modifications to the storage structure will be made to prevent condensation of moisture on the upper surface of the peanuts in future studies.

Most chill-cast commercial aluminum alloys, when inappropriately ingot grain refined, will contain twinned columnar growth (TCG) structures near the chill surface of the ingot. These structures consist of large grains composed of parallel arrays of continuous thin lamellae. Each lamella contains a central {111} coherent twin boundary and a noncoherent rough boundary at the edges. This paper describes the stability of such grain structures as affected by composition and postcasting processes such as ingot preheating and deformation. A series of simple binary and two complex high-strength aluminum alloys were investigated. In single-phase alloys, such as preheated binary alloys with compositions less than the maximum solid solubility, the TCG structure was eliminated by a grain growth process. In dual- and multiphase alloys, the stability of the structure depends on the size and distribution of particles after preheating and the nature of the particle/matrix interface. The interplay between particle stability, size, and distribution controls the stability of the TCG-containing microstructure during postcasting processing.

Following solidification, an aluminum alloy microstructure is highly segregated. The microstructure consists of cored dendrites with various soluble and insoluble phases present in the dendritic regions. The solidification rate has a marked effect on the amount of coring that an alloy experiences. Understanding the effects of the solidification rate is important in explaining differences in microstructures. Subsequent heat treatments are performed to homogenize the microstructure. The microstructure evolution after each processing step is dependent upon the previous microstructures. The variation in local chemical composition may promote or hinder precipitation of new phases. A large volume fraction of coarse insoluble phases can lead to the occurrence of recrystallized grains via particle stimulated nucleation, while inhomogeneous solute distribution can lead to the precipitation of an uneven distribution of dispersoid phases. The effect of solidification rate and subsequent thermal treatments on the microstructure of an Al-4Cu alloy will be investigated and experimental and numerical results will be presented.Copyright © 2003 by ASME

The alumina-chromia system shows complete mutual solubility and is represented by an isomorphous phase diagram. However, the alumina-chromia system exhibits an asymmetric miscibility gap under 1300°C. Using existing data from the literature, the alumina-chromia system was assessed using thermodynamic modeling by Kim and Sanders [1]. Regular and subregular solution models for the liquid and solid phases were used to define the phase boundaries for the miscibility gap in this system. Using this thermodynamic representation of the miscibility gap to select temperatures of interest, 75 mole percent Al2O3samples were synthesized via combustion of powders, followed by pressing into pellets and heat-treated for various times and temperatures. Both X-ray and TEM analysis showed evidence of spinodal decomposition after heat-treatment. X-ray analysis showed that decreasing the heat-treatment temperature increases the compositional difference between the phases present. The experimentally observed microstructures exhibit lamella-like structures that vary in spacing from 8nm to 3nm as the heat-treatment temperature varies from 400°C to 800°C.

Closed-cell metallic foams were fabricated by bonding millimeter sized hollow spheres at points of contact. The composition of low density metallic foams with hollow sphere architecture achieved to date includes Ti-6Al-4V, 400 series stainless steel, and Inconel 718. Hollow spheres are formed as powder shells from slurries of non-metallic precursor powders at room temperature. Subsequent heat treatment coupled with either direct reduction or hydride-dehydride processing converts precursors into the appropriate metal alloys . To produce titanium alloy spheres, the starting powder is titanium alloy hydride. Thermal treatment in an inert atmosphere decomposes the hydride and sinters the titanium powder in the sphere walls to greater than 96% relative density. Both titanium and Ti-6V-4V spheres and foams have been produced. However, oxygen content remains a concern for the titanium compositions explored and the titanium alloy foams produced so far behave like brittle foam. For stainless steel spheres, the starting powder is a mixture of iron and chromium oxide. Thermal treatment in hydrogen reduces the oxides to Fe-Cr alloys with less than 2% porosity in sphere walls. The nominal composition is close to that of 405 stainless. Carburization in CO/CO2 atmosphere followed by heat treatment produces foams of either 410 or 420 type stainless steels depending on carbon content. Compressive stress-strain behavior was measured on point contact bonded stainless foams both before and after carburization. A sample with 0.5 wt% carbon at a relative density of 15% indicated a yield strength of 16 MPa. Specific strengths of the foams were positioned between open and closed cell models. This was encouraging because bonding in the foams was less than optimum and the hollow sphere walls contained numerous defects. With improvements in processing, strengths should increase while maintaining ductility.

A hydrophobic fluorescence probe, 1,8-anilinonaphthalene sulfonate (ANS), was used to study the changes in protein surface hydrophobicity (PSH) occurring during peanut maturation and curing. PSH increased with the degree of maturity and during curing (windrow drying). The increase of PSH during curing or heating was more pronounced in immature peanuts than their mature counterparts, suggesting that more hydrophobic sites are hidden in the former proteins. PSH decreased when proteins were chemically modified with phenylglyoxal (an arginine-modifying agent), suggesting that arginine might play a role in hydrophobicity. The findings indicate that maturation and curing affect PSH, and that there is a relationship between PSH and peanut maturity. Possible factors contributing to the increase of PSH are discussed.

The evolution of dendritic morphology is simulated for a binary alloy using a two-dimensional cellular automaton growth algorithm. Solute diffusion is modeled with an alternate-direction implicit finite difference technique. Interface curvature and kinetic anisotropy are implemented through configurational terms which are incorporated into the growth potential used by the automaton. The weighting of the anisotropy term is explored and shown to be essential for overcoming grid-induced anisotropy, permitting more realistic development of dendritic morphologies. Dendritic structures are generated for both uniform and directional cooling conditions.

Lightweight stainless steel foams approaching 10% theoretical density are being fabricated via direct reduction. These foams are formed using a coaxial nozzle process that generates hollow ceramic spheres at high rates from an acetone-based slurry. The Fe2O3/Cr2O3 hollow spheres are reduced in a hydrogen/argon atmosphere at high temperature resulting in individual hollow metal spheres. Using more viscous slurry of similar composition, the spheres are bonded at points of contact into a quasi-closed cell structure and further heat treated to reduce the bond phase. The result is a Fe-12Cr alloy hollow sphere foam with a density on the order of 1 g/cc. Addition of carbon and further heat treatments allow the control of strength and ductility through micro structure. Mechanical testing is being conducted to determine attainable properties that can be compared to existing foam models.

The spall properties of rolled Al 5083-H116 plate are investigated using symmetric plate impact experiments over the stress range 1.5–6.2 GPa. Rear free surface velocity measurements made employing Velocity Interferometer System for Any Reflector interferometry reveal velocity profiles with clear signals of the Hugoniot elastic limit (HEL) and velocity pullback, indicative of a transition from elastic to plastic behavior and spalling. Experiments were performed on samples obtained both through the thickness and along all of the three principal axes of the rolled plate. For impact through the thickness, the average values of the HEL and spall strength are 0.43 GPa and 0.81 GPa, respectively. Decreasing the flyer plate and sample thicknesses resulted in an increased spall strength value of 0.95 GPa, while the HEL remained the same. The spall strength along the longitudinal (rolling) direction was 1.06 GPa versus 0.95 GPa for impact along either transverse direction. Spall damage for this impact direction often propagated away from the spall plane in the direction of impact and along the grain boundaries. For impact through the thickness, the fracture surface revealed a mixed mode of ductile and intergranular fracture that was not present for the fracture surface in the other two directions. This mixed fracture mode seems to correspond to a shoulder observed in the free surface velocity traces after the pullback. In all cases, cracked brittle inclusions were observed near the spall damage regions, indicating their role in nucleating voids during spall failure.

A novel method of fabricating low-density hollow sphere metallic foam has been developed. Utilizing pre-existing technology, thin-wall, hollow oxide spheres, ∼ 2mm in diameter, were formed from powder slurries with a coaxial nozzle process. Oxide foams were constructed by bonding sintered spheres at points of contact and firing. The oxide foams were reduced to the metallic state in a hydrogen atmosphere. Successful precursor compositions for transformation included NiO, Cu2O, and NiO-Cu2O. After reduction, the metal foams were sintered to increase strength and resulting foam densities were generally 10–20% of theoretical density. Wall thickness of the spheres which constitute the foams ranged from 50–100 μ m. Nickel foams were crushed under uniaxial compressive stress, and mechanical properties (yield stress, elastic modulus, and energy absorption) were investigated under varying density in order to determine parametric relationships to compare to existing models of foam properties. The effects of sintering, reduction, and compressive deformation on the microstructures were examined with SEM and EDS.

Thermogravimetric analysis was used to obtain corrosion kinetics data for several materials in high-temperature environments. A thermogravimetric analyzer has been developed that uses a McBain-Bakr quartz spring balance in conjunction with a digital image acquisition and analysis package to accurately characterize materials through image correlation. This provides a new method for automatically measuring mass changes continuously with a variable resolution depending on the spring component. The decomposition of calcium oxalate was used to verify the validity of the technique. The results show two reactions, whose reaction temperatures were determined by the intercept method, upon heating to 650 °C. The mass loss at the first reaction temperature, 200 °C, was 20% and a 30% loss was observed at 500 °C. Comparison of the experimentally obtained results with those of other researchers who used commercial instruments suggests that the method of using digital image analysis in conjunction with a spring to monit...

Stellite alloy no. 21 was produced via rapid solidification processing (RSP) in a variety of particulate morphologies (coarse and fine powder, fibres, and ribbons), the various RSP forms showed similar fine microstructures with only slight differences in the scale of the microstructural features. These RSP particulates were consolidated by extrusion, dynamic compaction, and rapid omnidirectional compaction (ROC). Dynamic compaction proved to be unacceptable for this alloy because of non-uniform porosity and the inability to develop a metallurgical bond between particulates. A plot of elongation against yield strength depicted two yield strength-ductility relationships for the Co–Cr–Mo type alloys. As-ROC samples had a low yield strength-ductility relationship. However, after hot forging, the relationship shifted to a level comparable to similar material processed by conventional extruding and forging operations. Atomized powder size also affected the strength-ductility relationships of the extrude...

This paper describes the approach and results of recent work in our laboratories on identifying and solving the ductility problems which have plagued Al-Li alloys. In addition, specific property goals for developing new Al-Li alloys have been established. These include a) a 30% increase in modulus:density ratio, compared to 7075-T76, without significant loss in other properties, and b) a 20% increase in modulus:density ratio and a 20% increase in strength:density ratio compared to 7075-T76, without significant loss in other properties. Two approaches are being pursued, one using conventional ingot metallurgy (I/M) and the other using rapid solidification of fine particulate plus powder metallurgy (P/M) consolidation. The rapid solidification approach is designed to reduce or eliminate segregation effects, reduce the grain size, extend solid solubility of additional elements, and refine the dispersoid particle size. In some cases, we have made a comparison of the structure and properties of similar alloys fabricated by the two methods.

THE storage environment in a mechanically ventilated peanut warehouse filled with peanuts was monitored throughout 5 months of storage. Temperature and relative humidity sensors were located throughout a cross section of the peanut mass, in the overspace and outside the warehouse. Data were collected at 2-h intervals throughout storage. Isotherms and moisture gradients were constructed for various periods of storage which indicate the influence of outside and overspace temperatures and relative humidities on the environment in the peanut mass. Peanut quality was maintained during storge and the mean temperature and relative humidities remained within the ranges generally considered sate for peanut storage

The epidemiology of aflatoxin contamination in groundnuts, maize and cottonseed, the life cycle of the fungus from sources of primary and secondary inoculum, the mode of entry of A. flavus into the plant, seed infection and, finally, aflatoxin formation in the seed is reviewed.

Oils extracted from three varieties of mature peanuts with chloroform/methanol (2:1, v/v) or petroleum ether and oils extracted with petroleum ether from one variety at eight distinct physiological maturity stages were fractionated by TLC. The three varieties of mature peanuts were quantitatively similar in relative percentages of lipid classes regardless of extraction solvent; however, oil composition of the one variety changed with maturity. Generally, triacyl-glycerol percentage increased and percentage of all other fractions decreased with maturity. The calculated weight per seed of most fractions increased from the lowest maturity stage tested up through stage 10 or 11, which corresponds closely with apparent physiological maturity of the seed.

Stereospecific analysis of triacylglycerols from 4 peanut varieties grown for up to 3 years at 4 locations showed diversity in percentage fatty acid placement. Distribution of oleic and linoleic acids at each position was significantly correlated to the amount in the total triacylglycerol for varieties grown at one location. However, correlations for thesn-3 position were not significant when data from more than one location were analyzed together. Generally, higher percentages of oleic or linoleic acid in the triacylglycerol resulted in a greater proportion of the particular fatty acid in thesn-2 position. Apparently, fatty acid concentrations as influenced by growing location have a significant influence on peanut triacylglycerol structure.

Florunner peanuts (Arachis hypogaea L.) were grown during the 1984 season near Tifton, Georgia. Two planting dates spaced one month apart were used to obtain four weekly digging dates. Peanuts from each harvest were windrow dried for 4 days, mechanically harvested and placed into a ventilated wagon for 1 to 4 days. Peanuts were subsequently removed from the wagon, shelled at 8 to 22% moisture (wb), and microwave vacuum dried at nominal rates of 4, 8, 16, and 32 times the normal rate of conventional wagon drying. Harvest group, microwave treatment level, and order of processing were configured in a Latin Square design. Concurrent with each microwave run (MV), a separate portion of the shelled peanuts was deep bed dried (CS) and another portion was similarly dried but within shell (CH). Analyses of variance were performed to determine the significance of treatment type, microwave level, harvest group, and processing order differences on splitting and skin slippage tendencies, mold growth, and germination potential. No significant (p> .05) differences were observed among treatment types for splitting and skin slippage potential, though slight (p< .05) differences existed among microwave treatment levels (damage increasing with increasing microwave drying rate), and drying order within microwave treatment (damage decreasing with increasing drying order). Larger (p< .01) splitting and skin slippage differences existed among harvest groups. MV treatments had significantly (p< .01) higher presence of A. flavus than the CS and CH treatments though aflatoxin was not detected in any sample. The percentage of normal strong germinated kernels from MV treatments was significantly (p

The effect of microstructure on the monotonic and low cycle fatigue properties of a high purity, large grain, ternary aluminum-zinc, magnesium (Al-Zn-Mg) alloy and a high strength 7050 aluminum alloy was investigated. The best combination of fatigue life, strength, and ductility for the ternary alloy resulted when aged to produce a microstructure containing predominately η′ having a Guinier radius of approximately 65a and a small amount of incoherent η (MgZn2). Superior fatigue life, strength, and ductility were found when the 7050 alloy was aged to produce the maximum number of partially coherent η′ precipitates having a Guinier radius of approximately 35a. Aging the 7050 alloy to produce particles larger than 50a gave a microstructure that had lower fatigue properties at the low plastic strain amplitudes, δep/2

A comparison of the invasion of flowers, aerial pegs, and kernels by wild-type and mutant strains of Aspergillus flavus or A. parasiticus along with aflatoxin analyses of kernels from different drought treatments have supported the hypothesis that preharvest contamination with aflatoxin originates mainly from the soil. Evidence in support of soil invasion as opposed to aerial invasion was the following. A greater percentage of invasion of kernels rather than flower or aerial pegs by either wild-type A. flavus or mutants. Significant invasion by an A. parasiticus color mutant occurred only in peanuts from soil supplemented with the mutant, whereas adjacent plants in close proximity but in untreated soil were only invaded by wild-type A. flavus or A. parasiticus. Aflatoxin data from drought-stressed, visibly undamaged peanut kernels showed that samples from soil not supplemented with a mutant strain contained a preponderance of aflatoxin B's (from wild-type A. flavus) whereas adjacent samples from mutant-supplemented soil contained a preponderance of B's plus G's (from wild-type and mutant A. parasiticus). Preliminary data from two air samplings showed an absence of propagules of A. flavus or A. parasiticus in air around the experimental facility.