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Contains fulltext : 174419.pdf (publisher's version ) (Open Access), Heparan sulfate (HS) proteoglycans represent a major component of the extracellular matrix and are critical for brain development. However, their function in the mature brain remains to be characterized. Here, acute enzymatic digestion of HS side chains was used to uncover how HSs support hippocampal function in vitro and in vivo. We found that long-term potentiation (LTP) of synaptic transmission at CA3-CA1 Schaffer collateral synapses was impaired after removal of highly sulfated HSs with heparinase 1. This reduction was associated with decreased Ca2+ influx during LTP induction, which was the consequence of a reduced excitability of CA1 pyramidal neurons. At the subcellular level, heparinase treatment resulted in reorganization of the distal axon initial segment, as detected by a reduction in ankyrin G expression. In vivo, digestion of HSs impaired context discrimination in a fear conditioning paradigm and oscillatory network activity in the low theta band after fear conditioning. Thus, HSs maintain neuronal excitability and, as a consequence, support synaptic plasticity and learning.

The microstructure, phase composition and mechanical properties of the AlMo0.5NbTa0.5TiZr and Al0.4Hf0.6NbTaTiZr high-entropy alloys are reported. The AlMo0.5NbTa0.5TiZr alloy consists of two body-centered cubic (bcc) phases with very close lattice parameters, alpha 1 = 326.8 pm and alpha 2 = 332.4 pm. One phase was enriched with Mo, Nb and Ta and another phase was enriched with Al and Zr. The phases formed nano-lamellae modulated structure inside equiaxed grains. The alloy had a density of rho = 7.40 g/cu cm and Vickers hardness Hv = 5.8 GPa. Its yield strength was 2000 MPa at 298 K and 745 MPa at 1273 K. The Al0.4Hf0.6NbTaTiZr had a single-phase bcc structure, with the lattice parameter alpha = 336.7 pm. This alloy had a density rho = 9.05 g/cu cm, Vickers microhardness Hv = 4.9 GPa, and its yield strength at 298 K and 1273 K was 1841 MPa and 298 MPa, respectively. The properties of these Al-containing alloys were compared with the properties of the parent CrMo0.5NbTa0.5TiZr and HfNbTaTiZr alloys and the beneficial effects from the Al additions on the microstructure and properties were outlined. A thermodynamic calculation of the solidification and equilibrium phase diagrams was conducted for these alloys and the calculated results were compared with the experimental data., Journal article published in Acta Materialia 68 (2014) 214-228. See also AFRL-RX-WP-TP-2014-0134, AFRL-RX-WP-JA-2014-0167, AFRL-RX-WP-JA-2014-0170, and AFRL-RX-WP-JA-2014-0177.

Equimolar FeCoCrNi alloys have been the topic of recent research as high-entropy alloys, where the name is derived from the high configurational entropy of mixing for a random solid solution. Despite their name, no systematic study of ordering in this alloy system has been performed to date. Here, we present results from anomalous x-ray scattering and neutron scattering on quenched and annealed samples. An alloy of FeNi3 was prepared in the same manner to act as a control. Evidence of long-range chemical ordering is clearly observed in the annealed FeNi3 sample from both experimental techniques. The FeCoCrNi sample given the same heat treatment lacks long-range chemical order., Published in Applied Physics Letters, v100 article ID 251907, 20 Jun 2012. Prepared in cooperation with UTC, Inc., Dayton, OH, UES, Inc., Dayton, OH, California Institute of Technology, W. M. Keck Laboratory, Pasadena, Wright State University, Dayton, OH, Oak Ridge National Laboratory, Oak Ridge, TN and Argonne National Laboratory, Argonne, IL.

The atomic structures of several Ca-Mg-Cu and Ca-Mg-Zn amorphous alloys have been determined using ab initio molecular dynamics simulation and neutron diffraction. Partial pair distribution functions have been produced and the pair bond distances and partial coordination numbers have been reported for these alloys. Similarities and differences in the amorphous structures of the Ca-Mg-Cu and Ca-Mg-Zn alloys have been discussed.

Rene88 samples were investigated using atom probe tomography and x-ray diffraction using a monochromated synchrotron beam with different energy values to determine the preferred site occupancy of various alloying elements within the ordered gamma/ precipitates. Samples were solutionized and cooled at 24 degree C/min with subsequent aging at 760 degrees C. The synchrotron-based x-ray diffraction results indicate that niobium prefers to reside on the aluminum sublattice site of the gamma phase. Additionally, the experimental results also indicate that chromium prefers the nickel sublattice sites while cobalt is likely to occupy both the aluminum and nickel sublattice sites. The x-ray results on the chromium occupancy disagree with atom probe results from the same alloy that indicate that chromium prefers the aluminum sublattice sites. Modeling studies indicate cobalt has no strong site preference., Prepared in collaboration with(University of North Texas, and Institute of Advanced Composite Materials, Korea Institute of Science and Technology.

Isothermal oxidation behavior of a refractory high entropy NbCrMo0.5Ta0.5TiZr alloy was studied during heating at 1273 K for 100 hours in flowing air. Continuous weight gain occurred during oxidation and the time dependence of the weight gain per unit surface area was described by a parabolic dependence with the time exponent n = 0.6. X-ray diffraction and scanning electron microscopy (SEM) accompanied by energy dispersive X-ray spectroscopy (EDS) showed that the continuous oxide scale was made of complex oxides and only local (on the submicron levels) redistribution of the alloying elements occurred during oxidation. The alloy has a better combination of mechanical properties and oxidation resistance than commercial Nb alloys and earlier reported developmental Nb-Si-Al-Ti and Nb-Si-Mo alloys., Prepared in cooperation with UES, Inc. Submitted to Materials Science and Engineering.

A new refractory alloy, Nb20Cr20Mo10Ta10Zr20Ti20, was produced by vacuum arc melting. To close shrinkage porosity, it was hot isostatically pressed (HIPd) at T = 1723 K and P = 207 MPa for 3 hours. In both as-solidified and HIPd conditions, the alloy contained three phases: two body centered cubic (BCC1 and BCC2) and one face centered cubic (FCC). The BCC1 phase was slightly enriched with Nb, Mo and Ta and depleted with Zr and Cr, and its lattice parameter after HIP was a = 324.76 plus or minus 0.16 pm. The BCC2 phase was enriched with Zr and Ti and considerably depleted with Mo, Cr and Ta, and its lattice parameter after HIP was estimated to be a = 341.0 plus or minus 1.0 pm. The FCC phase was highly enriched with Cr and it was identified as a Laves C15 phase, (Zr,Ta)(Cr,Mo,Nb)2, with the lattice parameter a = 733.38 plus or minus 0.18 pm. The volume fractions of the BCC1, BCC2 and FCC phases were 68.5%, 9.6% and 21.9%, respectively. The alloy density and Vickers microhardness were = 8.23 plus or minus 0.01 g/cubic cm and Hv = 5288 plus or minus 71 MPa. The alloy had compression yield strength of 1595 MPa at 296 K, 983 MPa at 1073 K, 546 MPa at 1273 K and 171 MPa at 1473 K. During deformation at 296 K and 1073 K, the alloy showed ductile fracture after plastic compression strain of approximately 5-6%. No macroscopic fracture was observed after 50% compression strain at 1273 K and 1473 K., Preprint journal article to be submitted to Acta Materialia. Prepared in collaboration with UES, Inc., Dayton, OH. This document contains color.

The atomic structures of four Ca40+XMg25Cu35-X (X = 0, 5, 10, and 20 at.%) ternary metallic glasses have been determined using a synergistic combination of neutron diffraction, quantum molecular dynamic (QMD) simulation and constrained reverse Monte Carlo modeling. The amorphous structure of these alloys can be described as close-packing of efficiently packed Cu-centered clusters that have Ca, Mg and Cu atoms in the first coordination shells. Experimental evidence is given for the presence of Cu atoms in inter-cluster sites for the two most Cu-rich glasses. The close-packed arrangement of clusters is present only within length scale a length scale of approximately 10 A providing a characteristic medium range order prepeak at Q approximately 1.2 A in the total scattering structure factors of these alloys. An average coordination number of 10 (with about 5-7 Ca, 2-3 Mg and 1-2 Cu atoms) is most common for the Cu-centered clusters. The average coordination numbers around Mg and Ca are 12-13 (approximately 6-8 Ca, 3 Mg and 1-4 Cu) and 13-15 (7-9 Ca, 3-4 Mg, and 2-5 Cu), respectively, and they are composition dependent., Journal article submitted to Physical Review B. Prepared in collaboration with the Department of Materials Science and Engineering, John Hopkins University, Baltimore, MD and ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, United Kingdom.

The amorphous structure of four Ca60MgXZn40-X alloys (X = 10, 15, 20, and 25 at.%) has been modeled using a set of experimental neutron and X-ray scattering data, peak fit analysis, and Reverse Monte Carlo (RMC) simulation. The amorphous structure can be described as a mixture of Mg- and Zn- centered clusters, with Ca dominating in the first coordination shell of these clusters. The coordination number (CN) of 10 (with about 7 Ca and 3 (Mg+Zn) atoms) is the most common for the Zn-centered clusters. CN = 11 and 12 (with about 7-8 Ca and 4 (Mg+Zn) atoms) are the most common for the Mg-centered clusters. Fife-fold bond configurations (pentagonal pyramids) dominate (60%) in the first coordination shell of the clusters, suggesting densely atomic packing. Bond angle distributions suggest the near-equilateral triangles and pentagonal pyramids to be the most common nearest atom configurations. Two Ca-Mg-Zn alloys with inferior GFA have increased amounts of (0,0,12,0), (0,2,8,1), (0,2,8,2) and (0,4,4,3) clusters, which suggests that these clusters may facilitate crystallization., Journal article submitted to Metallurgical and Materials Transactions A.

Two refractory high entropy alloys with concentrations near Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20, were produced by vacuum arc-melting. Despite containing many constituents both alloys had a single-phase body-centered cubic (BCC) structure that remained stable after exposure to 1400 deg C. Compression properties of the alloys were determined in the temperature range of room temperature to 1600 deg C. Limited compressive plasticity and quasi-cleavage fracture at room temperature suggests that the ductile-to-brittle transition for these alloys occurs above room temperature. At 600 deg C and above, both alloys showed extensive compressive plastic strain. The yield strength dropped by 30-40% between room temperature and 600 deg C, but was relatively insensitive to temperature above 600 deg C . The yield strength values of both alloys were high over the entire temperature range relative to conventional superalloys., Submitted to the Journal of Alloys and Compounds. Prepared in collaboration with UES, Inc., Dayton, OH and General Dyamics Corp., Dayton, OH.

A refractory alloy, Ta20Nb20Hf20Zr20Ti20, was produced by vacuum arc-melting. The as-solidified alloy had a dendritic structure, which was not affected by hot isostatic pressing (HI Ping) conducted at T = 1200 deg C and p = 207 MPa for 3 hours. The alloy had a single-phase body-centered cubic (BCC) structure with the lattice parameter a= 340.44 pm. The alloy density and Vickers microhardness after HIPing were p = 9.94 g/cm3 and Hv = 3826 MPa. Room temperature compression testing of HIPd samples revealed excellent ductility. The samples deformed homogeneously without any evidence of cracking at least up to 50% compression strain. Continuous strengthening followed yielding at 807 MPa. A simple model of solid-solution strengthening is proposed to explain the behavior., Prepared in collaboration with UES Inc., Dayton, OH. Journal article submitted to Jnl of Alloys and Compounds.

Two refractory alloys, W-Nb-Mo-Ta and W-Nb-Mo-Ta-V, with near-equiatomic compositions were produced by vacuum arc-melting. Both alloys have a single-phase body-centered cubic (BCC) structure. The lattice parameters a = 3.2134 A for the quaternary alloy and a = 3.1832 A for the quinternary alloy were determined with the use of a high-energy X-ray diffraction and the scattering vector length range from 0.7 to 20 A-1. The alloy density and Vickers microhardness were p = 13.75 g/cm3 and Hv = 4455 MPa for the W-Nb-Mo-Ta alloy and p = 12.36 g/cm3 and Hv = 5250 MPa for the W-Nb-Mo- Ta-V alloy. The higher microhardness was related to the finer grain structure in the quinternary alloy., Prepared in cooperation with Air Force Research Lab., General Dynamics, Dayton, OH and Tennessee Univ. Jnl article submitted to Jnl of Alloys and Compounds.

The effect of heat treatment on precipitation and growth of coherent nanometer-sized Al3(Sc,Zr) particles and the effect of these particles on tensile properties of a direct chill (DC) cast Al-Zn-Mg-Cu-Sc-Zr alloy were studied. The size distribution, average size, number density and volume fraction of the Al3(Sc,Zr) particles were determined as a function of the solution treatment temperature and time. The average particle diameter increased from 6.0 nm to 27.3 nm, the volume fraction increased from 0.11% to 0.46%, while their number density decreased from 5.4x10(exp 15) cm-3 to 3.1x10(exp 14) cm-3 with an increase in the solution treatment temperature from 460deg C to 480 deg C and holding time from 1 hour to 48 hours. The particle size distributions were well described by normal (Gaussian) distributions but did not follow the Lifshitz-Slyozov-Wagner (LSW) theory of Ostwald ripening. To describe the observed particle size distributions, a stochastic process of particle growth was added to the normal process of growth. The kinetics of phase transformation followed the Kolmogorov-Johnson-Mehl-Avrami (KJMA) law, with the Avrami exponent m = 0.404., Submitted for publication in Acta Materialia. Prepared in collaboration with Air Force Research Laboratory (AFRL), Wright-Patterson AFB, OH.

The effect of Al addition on glass forming ability and glass stability of Ca-Mg-Zn, Ca-Mg-Cu, and Ca-Mg-Zn-Cu alloys was studied. The glassy alloys were produced by a copper mold casting method as wedge-shaped samples with thicknesses varying from 0.5 mm to 10 mm. Thermal properties, such as the glass transition, crystallization and melting temperatures, as well as heats of crystallization and melting, were determined for the produced glasses. Partial substitution of Zn and/or Cu with Al was found to generally reduce the glass forming ability; however, it improves the glass stability., Submitted to Metallurgical and Materials Transactions A. The U.S. Government is joint author of this work and has the right to use, modify, reproduce, release, perform, display, or disclose the work. The original document contains color images.

Bulk amorphous metals are attractive materials for several reasons. An absence of microstructural features such as crystal plains, dislocations, grain and phase boundaries contribute to appealing mechanical properties such as high hardness and high specific strength. The amorphous structure also results in attractive magnetic properties such as high magnetic permeability. Corrosion studies have also established amorphous metals as a group of materials with corrosion properties much more desirable than their crystalline counterparts. As a result, metallic glasses have found their way into common applications including golf club heads, magnetic security strips, step-down transformers and cell phone cases. Within the last 15 years, many successful steps have been made in both understanding the properties of amorphous metals and in processing bulk quantities efficiently. Calcium based bulk metallic glasses constitute a new class of amorphous materials., Submitted for publication in the 2006 Proceedings of the 5th International Bulk Metallic Glasses Conference, in a special issue of the Journal, Materials Transaction, published by the Japan Inst. of Metals.

Low density Ca-Mg-Al-based bulk metallic glasses containing additionally Cu and Zn, were produced by a copper mold casting method as wedge-shaped samples with thicknesses varying from 0.5 mm to 10 rom. The compositions of the alloys were selected using recently developed specific criteria for glass formation. A structural assessment using the efficient cluster packing model was also applied and showed a good ability to represent these glasses. Thermal properties of the new metallic glasses, such as the glass transition, crystallization and melting temperatures, as well as heats of crystallization and melting are reported. The critical cooling rate for amorphization and the fragility index are estimated for these alloys. The effect of the alloy composition on glass forming ability is discussed.

This paper was developed under a SBIR contract. The effect of Sc additions on precipitation strengthening in AI-Zn-Mg-Cu alloys was studied after natural and artificial aging. Phase analysis was performed using transmission electron microscopy and computer simulations. Microhardness of the alloys was studied after different steps of aging and the strengthening mechanisms were discussed. It was found that Sc does not affect the kinetics of aging at room temperature, which is controlled by formation and growth of GPI zones. Sc also does not affect the kinetics of aging at 150C, which is controlled by formation and growth of eta' and eta particles. However, the additions of Sc accelerate the aging process at l20C within a period of time of formation and growth of GPII zones. It is concluded that the presence of Sc accelerates formation and growth of GPII zones in the Al-Zn-Mg-Cu alloys during artificial aging.

A number of ternary Ca-Mg-Cu amorphous alloys with compositions ranging from 40 to 70 at. % for Ca, 5 to 25 at. % for Mg, and 10 to 35 at. % for Cu were produced by a copper mold casting method as wedge-shaped samples with the thickness varying from 0.5 mm to 10 mm. The maximum thickness at which an alloy remains fully amorphous, glass transition temperature, crystallization temperature, temperature interval of the super-cooled region, solidus and liquidus temperatures, as well as heats of crystallization and melting, are reported for these alloys. The effect of the alloy composition on glass forming ability is discussed. In the studied composition range, the Ca50Mg22.5Cu27.5 alloy has the best glass forming ability, being fully amorphous after casting to the thicknesses of at least 10 mm.

The purpose of this research is to establish structure forming principles that govern the atomic structures of metallic glasses. A structural model based on efficient atomic packing will be discussed and applied to the topological systems that represent most metallic glass alloys. The concept of efficient atomic packing has direct and specific implications regarding the local structure and composition of metallic glasses. Specific solute-to-solvent atomic radius ratios and specific solute concentrations related to these ratios are shown to be preferred in this model, and analysis of a wide range of metallic glass systems shows a very strong correlation with these predicted values. Relationships between atomic size and concentration are discussed, and new insights are proposed based on the current structural model. Possible local atomic configurations (i.e., atomic clusters) are defined based on topological constraints that are derived from the requirement of efficient atomic packing. Experimental observations drawn from the literature that provide support for this model are presented., Presented at the International Conference on Rapidly Quenched and Metastable Materials (11th) held at Oxford Univ., Oxford, United Kingdom on 25-30 Aug 2002. Pub. in Materials Science and Engineering A, vA375-377 p150-156, 2004. Sponsored in part by the Air Force Office of Scientific Research. This article is from ADA433169 International Conference on Rapidly Quenched and Metastable Materials (11th), Held at Oxford University, U.K. on 25-30 August 2002

The effect of combined additions of Sc and Zr on the microstructure and tensile properties of the direct chill (DC) cast ingots of developmental Al-Zn-Mg-Cu alloys has been evaluated in this work. The properties in both the longitudinal and transverse directions of the cast ingots were determined in as-cast and cast plus heat-treated conditions, at room and cryogenic temperatures. Extensive microstructural evaluation was carried out using optical and electron microscopy, including orientation image microscopy by the electron backscatter diffraction technique. The Sc-containing developmental cast alloys showed the tensile properties, which are much better than the properties of any commercial cast Al alloys and are similar or even superior to the properties of 7075-T6 alloy forgings. The microstructural evolution, the strengthening mechanisms, optimum content of the dispersoid-forming elements, and the processing-structure-property correlations are discussed.

Four developmental 7XXX series alloys modified with Sc, Zr and other dispersoid-forming elements were produced by continuous direct chill (DC) casting. Microstructure and mechanical properties were evaluated in both the longitudinal and transverse directions at room and cryogenic temperatures. The homogenization, solution treatment and aging schedules were optimized to obtain superior mechanical properties. In particular, the Sccontaining cast alloys showed tensile properties similar or even superior to the properties of a wrought 7075-T6 alloy. The strengthening mechanisms responsible for this improvement, optimal Sc content and the processing parameters are discussed.

Briefing charts from presentation on the development of super-high strength aluminum alloys for cryogenic applications., See also ADM001672. Presented at NATO Advanced Research Workshop on Metallic Materials with High Structural Efficiency held in Kiev, Ukraine on 7-13 Sep 2003. The original document contains color images.

ELECTRONIC FILE CHARACTERISTICS: 66 files; MS Word (.DOC), Adobe Acrobat (.PDF), and MS PowerPoint (.PPT). PHYSICAL DESCRIPTION: 1 computer laser optical disc (CD-ROM); 4 3/4 in.; 176 MB. SYSTEMS DETAIL NOTE: ABSTRACT: This CD-ROM contains the presentations from the NATO Advanced Research Workshop on Metallic Materials with High Structural Efficiency., Presented at the NATO Advanced Research Workshop on Metallic Materials with High Structural Efficiency held in Kiev, Ukraine on 7-13 September 2003.

An amorphous, 150 micrometers thick freestanding sheet of a TiAl-based alloy was produced by a physical vapor deposition method. The following phase transformations were observed and analyzed using differential thermal analysis and X-ray diffraction, amorphous body centered cubic beta hexagonal close-packed alpha tetragonal gamma + ordered HCP alpha(sub 2).