High temperature deformation processing maps for boron modified Ti-6Al-4V alloys

The alloy, Ti-6Al-4V is an alpha + beta Ti alloy that has large prior beta grain size (similar to 2 mm) in the as cast state. Minor addition of B (about 0.1 wt.%) to it refines the grain size significantly as well as produces in-situ TiB needles. The role played by these microstructural modifications on high temperature deformation processing maps of B-modified Ti64 alloys is examined in this paper.Power dissipation efficiency and instability maps have been generated within the temperature range of 750-1000 degrees C and strain rate range of 10(-3)-10(+1) s(-1). Various deformation mechanisms, which operate in different temperature-strain rate regimes, were identified with the aid of the maps and complementary microstructural analysis of the deformed specimens. Results indicate four distinct deformation domains within the range of experimental conditions examined, with the combination of 900-1000 degrees C and 10(-3)-10(-2) s(-1) being the optimum for hot working. In that zone, dynamic globularization of alpha laths is the principle deformation mechanism. The marked reduction in the prior beta grain size, achieved with the addition of B, does not appear to alter this domain markedly. The other domains, with negative values of instability parameter, show undesirable microstructural features such as extensive kinking/bending of alpha laths and breaking of beta laths for Ti64-0.0B as well as generation of voids and cracks in the matrix and TiB needles in the B-modified alloys. (C) 2010 Elsevier B.V. All rights reserved.

Electron-beam melting and centrifugal splat-quenching technique for rapid solidification of titanium alloys

An electron-beam melting and centrifugal splat-quenching technique for the production of microflakes of Ti-6A1-4V (wt%) alloy quenched at an average cooling rate of about 105 K sec–1 is described. The effect of substrate angle on the shape, size, microstructure and average cooling rate of the flakes of major sieve fractions is discussed. Morphologies of particles of minor sieve fractions are dealt with briefly.

Conservadurismo, negación y diáspora

This contribution deals with social and political aspects affecting cultural life in Jalisco (Mexico), during the last forty years. It is, especially, a critical view on the regional deterioration of experimental music, analysing ethnic, religion, gender and other social components in one of the culturally foremost states of Mexico.

Design and fabrication of an automated temperature programmed reaction system to evaluate 3-way catalysts Ce1-x-y(La/Y)(x)PtyO2-delta

A completely automated temperature-programmed reaction (TPR) system for carrying out gas-solid catalytic reactions under atmospheric flow conditions is fabricated to study CO and hydrocarbon oxidation, and NO reduction. The system consists of an all-stainless steel UHV system, quadrupole mass spectrometer SX200 (VG Scientific), a tubular furnace and micro-reactor, a temperature controller, a versatile gas handling system, and a data acquisition and analysis system. The performance of the system has been tested under standard experimental conditions for CO oxidation over well-characterized Ce1-x-y(La/Y)(y)O2-delta catalysts. Testing of 3-way catalysis with CO, NO and C2H2 to convert to CO2, N-2 and H2O is done with this catalyst which shows complete removal of pollutants below 325 degrees C. Fixed oxide-ion defects in Pt substituted Ce1-y(La/Y)(y)O2-y/2 show higher catalytic activity than Pt ion-substituted CeO2.

Superconducting Y--Ba--Cu--O Thin Films by RF Sputtering

Thin films of Y--Ba--Cu--O have been prepared by conventional methods of RF sputtering. The films exhibit superconducting onset temperatures as high as 91K, midpoint at 80K and a zero resistance state at 35K. Critical current measurements implied critical current densities of the order of 31 A/cm exp 2 . An attempt has been made to establish the role of substrate and various deposition parameters. 7 ref.--AA.

Theoretical Treatment of Interaction Parameters in Multicomponent Metallic Solutions

A new theoretical equation for interaction parameter in multicomponent metallic solutions is developed using the pseudopotential formalism coupled with the free energy of the hard sphere system. The approximate expression for the pseudopotential term is given in terms of the heat of solution at infinite dilution, to allow easy evaluation of the interaction parameter in various multicomponent systems. This theory has been applied to 23 non-ferrous alloys based on Pb, Sn, Bi and indium. Comparison with the results of previous theoretical calculations using only the hard sphere model suggests that the inclusion of the pseudopotential term yields a quantitatively more correct prediction of interaction parameters in multicomponent metallic solutions. Numerical calculations were also made for 320 Fe-base solutions relevant to steelmaking and the agreement between calculation and experimental data appears reasonable, with 90% reliability in predicting the correct sign.

Volume effects and associations in liquid alloys

The regular associated solution model for binary systems has been modified by incorporating the size of the complex as an explicit variable. The thermodynamic properties of the liquid alloy and the interactions between theA ?B type of complex and the unassociated atoms in anA-B binary have been evaluated as a function of relative size of the complex using the activity coefficients at infinite dilution and activity data at one other composition in the binary. The computational procedure adopted for determining the concentration of clusters and interaction energies in the associated liquid is similar to that proposed by Lele and Rao. The analysis has been applied to the thermodynamic mixing functions of liquid Al-Ca alloys believed to contain Al2Ca associates. It is found that the size of the cluster significantly affects the interaction energies between the complex and the unassociated atoms, while the equilibrium constant and enthalpy change for the association reaction exhibit only minor variation, when the equations are fitted to experimental data. The interaction energy between unassociated free atoms remains virtually unaltered as the size of the complex is varied between extreme values. Accurate data on free energy, enthalpy, and volume of mixing at the same temperature on alloy systems with compound forming tendency would permit a rigorous test of the proposed model.

Perunan Y-viruksen testaaminen korkeassa happi-hiilidioksidipitoisuudessa idätetyistä perunoista

Perunalla (Solanum tuberosum L.) tällä hetkellä maailmanlaajuisesti eniten sato- ja laatutappioita aiheuttaa perunan Y-virus (PVY). Vaikka pelkän Y-viruksen aiheuttamaa satotappiota on vaikea mitata, on sen arvioitu olevan 20-80 %. Viruksen tärkein leviämistapa on viroottinen siemenperuna. Korkealaatuinen siemenperuna on edellytys ruoka-, ruokateollisuus- ja tärkkelysperunan tuotannolle. Kasvuston silmämääräinen tarkastelu aliarvioi yleensä Y-viruksen esiintyvyyttä. Laboratoriotestauksen avulla saadaan tarkempi tieto pellolta korjatun sadon saastunta-asteesta. Ongelmana Y-viruksen testaamisessa on, että sitä ei havaita dormanssissa olevista perunoista otetuista näytteistä yhtä luotettavasti kuin jo dormanssin ohittaneista perunoista testattaessa. Erilaisia menetelmiä kemikaaleista (Rindite, bromietaani) kasvihormoneihin (mm. gibberelliinihappo) ja varastointiolosuhteiden muutoksiin (kylmä- ja lämpökäsittely) on kokeiltu perunan dormanssin purkamiseen, mutta tulokset ovat olleet vaihtelevia. Tässä tutkielmassa perunan dormanssin purkamiseen käytettiin happi-hiilidioksidikäsittelyä (O2 40 % ja CO2 20 %) eripituisina käsittelyaikoina. Tarkoituksena oli selvittää, vaikuttaako käsittely perunan itämiseen ja dormanssin luontaista aikaisempaan purkautumiseen tai Y-viruksen havaitsemiseen. Lisäksi haluttiin selvittää, voiko Y-viruksen määrittämisen ELISA-testillä (Enzyme Linked Immunosorbent Assay) tehdä yhtä luotettavasti myös muista kasvinosista (mukula, itu), kuin tällä hetkellä yleisesti käytetystä perunan lehdestä. Idätyskäsittelyn vaikutuksista dormanssin purkautumiseen saatiin vaihtelevia, eikä kovinkaan yleistettäviä tuloksia. Käsittelyn ei myöskään havaittu vaikuttavan PYY-viroottisuuden havaitsemiseen eri näytemateriaaleilla testattaessa. Kun eri kasvinosien toimivuutta testissä vertailtiin, mukulamateriaalin todettiin aliarvioivan PVY-viroottisuutta kaikissa kokeissa. Myös itumateriaali aliarvioi pääsääntöisesti PVY-viroottisuutta ELISA:lla tehdyissä määrityksissä. Luotettavin testimateriaali oli perunan lehti.

A molecular dynamics study of cage-to-cage migration in sodium Y zeolite: role of surface-mediated diffusion

The details of cage-to-cage migration have been obtained from an analysis of the molecular dynamics trajectory of a probe adsorbate. It is observed that particles utilize the region within a radius of 2 angstrom from the window center but with diffusion taking place predominantly at 1.6 angstrom from the window center and a potential energy of nearly -12 kJ/mol. A barrier of about 0.5 kJ/mol is observed for surface-mediated diffusion. Surprisingly, for diffusion without surface mediation for a particle going from one cage center to another, there is an attractive well near the window instead of a barrier. At low adsorbate concentrations and room temperature, the predominant mode for cage-to-cage migration is surface-mediated diffusion. The analysis suggests that particles slide along the surface of the inner walls of the alpha-cages during migration from one cage to another.

Electric and magnetic polarizabilities of hexagonal Ln(2)CuTiO(6)(Ln = Y, Dy, Ho, Er, and Yb)

We investigated the rare-earth transition-metal oxide series, Ln(2)CuTiO(6) (Ln = Y, Dy, Ho, Er, and Yb), crystallizing in the hexagonal structure with noncentrosymmetric P6(3)cm space group for possible occurrences of multiferroic properties. Our results show that while these compounds, except Ln = Y, exhibit a low-temperature antiferromagnetic transition due to the ordering of the rare-earth moments, the expected ferroelectric transition is frustrated by the large size difference between Cu and Ti at the B site. Interestingly, this leads these compounds to attain a rare and unique combination of desirable paraelectric properties with high dielectric constants, low losses, and weak temperature and frequency dependencies. First-principles calculations establish these exceptional properties result from a combination of two effects. A significant difference in the MO5 polyhedral sizes for M = Cu and M = Ti suppress the expected cooperative tilt pattern of these polyhedra, required for the ferroelectric transition, leading to relatively large values of the dielectric constant for every compound investigated in this series. Additionally, it is shown that the majority contribution to the dielectric constant arises from intermediate-frequency polar vibrational modes, making it relatively stable against any temperature variation. Changes in the temperature stability of the dielectric constant among different members of this series are shown to arise from changes in relative contributions from soft polar modes.

High-Temperature (1023 K to 1273 K 750 degrees C to 1000 degrees C]) Plastic Deformation Behavior of B-Modified Ti-6Al-4V Alloys: Temperature and Strain Rate Effects

A minor addition of B to the Ti-6Al-4V alloy, by similar to 0.1 wt pct, reduces its as-cast prior beta grain size by an order of magnitude, whereas higher B content leads to the presence of in situ formed TiB needles in significant amounts. An experimental investigation into the role played by these microstructural modifications on the high-temperature deformation behavior of Ti-6Al-4V-xB alloys, with x varying between 0 wt pct and 0.55 wt pct, was conducted. Uniaxial compression tests were performed in the temperature range of 1023 K to 1273 K (750 degrees C to 1000 degrees C) and in the strain rate range of 10(-3) to 10(+1) s(-1). True stress-true strain responses of all alloys exhibit flow softening at lower strain rates and oscillations at higher strain rates. The flow softening is aided by the occurrence of dynamic recrystallization through lath globularization in high temperature (1173 K to 1273 K 900 degrees C to 1000 degrees C]) and a lower strain rate (10(-2) to 10(-3) s(-1)) regime. The grain size refinement with the B addition to Ti64, despite being marked, had no significant effect on this. Oscillations in the flow curve at a higher strain rate (10(0) to 10(+1) s(-1)), however, are associated with microstructural instabilities such as bending of laths, breaking of lath boundaries, generation of cavities, and breakage of TiB needles. The presence of TiB needles affected the instability regime. Microstructural evidence suggests that the matrix cavitation is aided by the easy fracture of TiB needles.

Effect of magnesium addition and heat treatment on mild wear of hypoeutectic aluminium-silicon alloys

The effect of magnesium addition and subsequent heat treatment on mild wear of a cast hypoeutectic aluminium-silicon alloy when slid against EN 24 steel is studied. Morphology and chemistry of worn surface and subsurface are studied with a view to identify wear mechanism. Stability of an iron-aluminium mixed surface layer was found to be the key factor controlling wear resistance.

Effects of Zr and Ti doping on the dielectric response of CeO2: A comparative first-principles study

Zr doping in ceria (CeO2) results in enhanced static dielectric response compared to pure ceria. On the other hand, Ti doping in ceria keeps its dielectric constant unchanged. We use first-principles density functional theory calculations based on pseudopotentials and a plane wave basis to determine electronic properties and dielectric response of Zr/Ti-doped and oxygen-vacancy-introduced ceria. Softening of phonon modes is responsible for the enhancement in dielectric response of Zr-doped ceria compared to that of pure ceria. The ceria-zirconia mixed oxides should have potential use as high-k materials in the semiconductor industry. (c) 2010 Elsevier Ltd. All rights reserved.