1,720,959 research outputs found
Microstructure and bonding mechanism of Al/Ti bonded joint using Al-10Si-1Mg filler metal
No full textThe microstructures and liquid state diffusion bonding mechanism of cp-Ti to 1050 At using an Al-10.0wt.%Si-1.0wt.%Mg filler metal with 100 mum in thickness have been investigated at 620 degreesC under 1 X 10(-4) Torr. The effects of bonding process parameters on microstructure of bonded joint have been analyzed by using an optical microscope, AES, scanning electron microscopy and EDS. The interfacial bond strength of AIM bonded joints was measured by the single lap shear test. The results show that the bonding at the interface between At and filler metal proceeds by wetting the At with molten filler metal, and followed by removal of oxide layer on surface of Al. The interface between At and filler metal moved during the isothermal solidification of filler metal by the diffusion of Si from filler metal into At layer. The interface between At and filler metal became curved in shape with increasing bonding time due to capillary force at grain boundaries. The bonding at the interface between Ti and filler metal proceeds by the formation of two different intermetallic compound layers, identified as Al5Si12Ti7 and Al12Si3Ti5, followed by the growth of the intermetallic compound layers. The interfacial bond strength at AIM joint increased with increasing bonding time up to 25 min at 620 degreesC. However, the interfacial bond strength of Al/Ti joint decreased after bonding time of 25 min at 620 degreesC due to formation of cavities in At near Al/intermetallic interfaces. (C) 2003 Elsevier Science B.V. All rights reserved
High temperature deformation of Ti-(46-48)A1-2W intermetallic compounds
No full textThe high temperature deformation behavior of Ti-46Al-2W and Ti-48A1-2W intermetallic compounds have been investigated in isothermal compressive tests, performed at temperatures between 1000 degrees C and 1200 degrees C for strain rates between 10(-3) and 10(-1) s(-1). The stress-strain curve during high temperature deformation exhibits a peak stress which is followed by a gradual decrease into a steady state stress with increasing the strain. The flow softening behavior after the peak stress is attributed to the effects of dynamic recrystallization during deformation. The dependence of flow stress on temperature and strain rate followed a hyperbolic sine relationship using the Zener-Hollomon parameter. The activation energies, Q, were measured as 449 kJ mol(-1) and 394 kJ mol(-1), and the stress exponents were measured as 3.6 and 3.7 for Ti-46Al-2W and Ti-48A1-2W, respectively. The activation energy increased with decreasing Al content in TiAl-base intermetallic compounds. The coefficient between peak stress and Zener-Hollomon parameter, A, was not a constant, but was dependent on the activation energy. The peak stresses can be predicted well by using a normalized Zener-Hollomon parameter. The dynamic recrystallization rate and recrystallized grain size increased with increasing the temperature and with decreasing the strain rate. (C) 1998 Elsevier Science S.A. All rights reserved
Effects of particle shape and size on the homogeneity of dispersed U3Si particles in high uranium density research reactor fuels
No full textIn order to improve the homogeneity of the distributed U3Si fuel particles in the Al matrix of a high density research reactor fuel, the effect of the U3Si particle shape and size on the homogeneity of research reactor fuels has been investigated. The homogeneity of the distributed U3Si fuel particles in the Al matrix was evaluated by the apparent density measurement method. The homogeneity of a mixture consisting of comminuted irregular shaped U3Si particles and Al powders is superior to that of a mixture consisting of atomized U3Si particles and Al powders. From the measurement of the repose angle of the U3Si particles, it was noted that the cohesive strength of comminuted U3Si particles is higher than that of atomized U3Si particles, The homogeneity of a mixture consisting of finely atomized U3Si particles and Al powders is higher than that of a mixture consisting of coarsely atomized U3Si particles and Al powders, This result indicates that the cohesive strength of fine U3Si particles is higher than that of coarse U3Si particles. The homogeneity of U3Si/Al nuclear reactor fuel is improved by the formation of the an adsorbed layers between the U3Si and the Al powders. (C) 2001 Published by Elsevier Science B.V
Effect of Volume Fraction of SiC Particulate Reinforcement on Creep Properties of SiCp/2124A Metal Matrix Composites
No full textEffects of particle shape and size on the homogeneity of dispersed U3Si particles in high uranium density research reactor fuels
No full textEffect of SiC volume fraction on creep behavior of SiCp/2124Al metal matrix composite
No full textThe high temperature creep behavior of SiCp/2124Al metal matrix composites containing 10similar to30 vol.% of SiC particulate reinforcement was investigated to clarify the effect of the volume fraction of SiC particles on creep deformation. The SiCp/2124Al composites were fabricated by mixing 8mum SiC particles and 20mum 2124 Al powders and were followed by hot pressing at 570degreesC and hot extrusion at 500degreesC with an extrusion ratio of 25:1. The high temperature creep behavior of SiCp/2124Al composites was investigated by constant stress creep tests at 300degreesC. The load transfer phenomena of a spherical particle in metal matrix composite were analyzed based on the shear-lag model. The minimum creep rate of SiCp/2124Al composite decreased with increasing the volume fraction of SiC particles. The increase in the volume fraction of SiC particles reduces the effective stress for creep deformation of the Al matrix by the load transfer from the matrix to SiC particles. The minimum creep rates of SiCp/2124Al composites with different volume fractions of SiC particles were found to be similar under an identical effective stress on the matrix, which is calculated by the modified shear-lag model. It is suggested that the role of SiC particles is to increase the creep resistance by reducing the effective stress acting on the matrix in metal matrix composites
Development of advanced research reactor fuels using centrifugal atomization technology
No full textRotating disk centrifugal atomization technology has been utilized to fabricate uranium silicide (U3SI U3Si2) and U-Mo nuclear fuel powders having high uranium content per unit volume for high performance research reactor fuels. Atomized nuclear fuel powders have characteristics of a spherical shape with narrow size distribution, small specific surface area and high purity. The heat treatment time for the formation of U3Si by a peritectoid reaction was reduced from about 72 hours for comminuted powders to about 6 hours for atomized powders due to more rapid solidification of atomized powder with a finer microstructure. The homogeneity of fuel particles in fuel meats was improved by mixing atomized fuel powders with Al powders using a V-shaped tumbler mixer. The atomized powders with a spherical shape and smooth surface were extruded under lower force than the comminuted powders with angular rough surfaces. The dispersed fuel meat with atomized powders resulted in an increased fuel powder loading density and higher thermal conductivity in the heat flow direction. The thermal swelling of dispersed fuel meat decreased due to the reduced specific surface area of spherical atomized nuclear powder. The atomized U-10wt.%Mo dispersion fuel showed less bubble formation than the comminuted fuel after an irradiation test with 40% burnup
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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