1,720,958 research outputs found
Effects of solute and vacancy segregation on antiphase boundary migration in stoichiometric and Al-rich Fe₃Al: a phase-field simulation study
No full textEffects of segregation of solute atoms and vacancies on migration of antiphase boundaries (APBs) in stoichiometric (Fe-25 at%Al) and Al-rich (Fe-28 at%Al) Fe₃Al at 673 K have been studied using a phase-field method in which local vacancy concentration is taken into account [Koizumi Y, Allen SM, Minamino Y. Acta Mater 2008;56:5861, ibid. 2009;57:3039]. Boundary mobility (M) of APBs having different phase-shift vectors of a/4 and a/2 (hereafter denoted as B2-APB and D0₃-APB, respectively) was evaluated by measuring the boundary velocity of shrinking circular APBs. Similar effects of the segregation on the migration of B2-APBs were observed in both compositions. Vacancies segregated and Al-atoms were depleted at B2-APBs in both compositions. Vacancy concentration at B2-APBs was up to 80% higher than that in the bulk. As a result, the migration of B2-APBs was greatly enhanced by the vacancy segregation. In contrast, the segregation to D0₃-APBs showed a marked composition dependence. Vacancies were depleted and Al-atoms segregated at D0₃-APBs in the Al-rich Fe₃Al, whereas vacancies segregated and Al-atoms were depleted at D0₃-APB in the stoichiometric Fe₃Al. The Al segregation in the Al-rich Fe3Al decreased M of D0₃-APBs much more significantly than the Al-depletion in the stoichiometric Fe₃Al. As the APDs shrank, D0₃-APBs broke away from the segregation atmospheres and the M increased rapidly in both compositions. A greater increase in the M due to the breakaway was observed in the Al-rich Fe₃Al than in Fe₃Al with the stoichiometric composition.Iketani Science and Technology Promotion Foundatio
Effects of Solute and Vacancy Segregation on Migration of a/4<111> and a/2<100> Antiphase Boundaries in Fe₃Al
No full textThe effects of segregation of solute atoms and vacancies on migration of a/4〈1 1 1〉 and a/2〈1 0 0〉 antiphase domain boundaries (APDBs) in stoichiometric Fe3Al at various temperatures are studied using a phase-field model [Koizumi Y, Allen SM, Minamino Y, Acta Mater 2008;56:5861] based on the Bragg–Williams approximation and kinetic parameters determined from experimental data. Boundary mobilities (M) were measured from the boundary velocity of shrinking circular antiphase domains (APDs). In the case of a/4〈1 1 1〉 APDBs, solute atmospheres follow the APDB until the APD vanishes by shrinking to zero radius, and therefore the Ms are always smaller than the intrinsic boundary mobilities because of the solute-drag effect. The M of a/4〈1 1 1〉 APDBs can be enhanced by up to 60% by vacancy segregation. On the other hand, the M of a/2〈1 0 0〉 APDBs is enhanced by only a few per cent. The a/2〈1 0 0〉 APDBs are observed to break away from the solute atmosphere during as the circular ABDBs shrink. The M increases by up to 40% associated with the breakaway, and becomes equal to the intrinsic boundary mobilities even though slight depletion and segregation of Al atoms remain ahead and behind the migrating boundary, respectively
Frequency Response of Acoustic-Assisted Ni–Mn–Ga Ferromagnetic- Shape-Memory-Alloy Actuator
No full textA prototype of Ni–Mn–Ga based ferromagnetic-shape-memory-alloy (FSMA) actuator was designed and built; an acoustic-assist technique was applied to the actuator to enhance its performance. A piezoelectric stack actuator was attached to the Ni–Mn–Ga sample to generate acoustic energy to enhance twin-boundary mobility and, hence, reduce the magnetic threshold field required for activating twin-boundary motion. The dynamic response of the acoustic-assist FSMA actuator was measured up to 1 kHz actuation. The acoustic assistance improves the actuator performance by increasing the reversible magnetic-field-induced strain (MFIS) by up to 100% (increase from 0.017 to 0.03 at 10 Hz) for drive frequencies below 150 Hz. For frequencies above 150 Hz, the acoustic-assist effect becomes negligible and the resonant characteristic of the actuator takes over the actuator response. Even though the acoustic assist does not improve the actuation at high frequencies, the MFIS output of 5% can be obtained at the resonant frequency of 450 Hz without acoustic assistance. The FSMA actuator is shown to be ideal for applications that require large strain at a specific high frequency.United States. Office of Naval Research (Multi-University Research Initiative, Grant No. N0014-01-0758
The Impact of Weld Metal Creep Strength on the Overall Creep Strength of 9% Cr Steel Weldments
No full textIn this work, three joints of a X11CrMoWVNb9-1-1 (P911) pipe were welded with three filler metals by conventional arc welding. The filler metals varied in creep strength level, so that one overmatched, one undermatched, and one matched the creep strength of the P911 grade pipe base material. The long-term objective of this work was to study the influence of weld metal creep strength on the overall creep behavior of the welded joints and their failure mechanism. Uniaxial creep tests at 600°C and stresses ranging from 70 MPa to 150 MPa were performed on the cross-weld samples of all three welds. A total creep testing time of more than 470,000 h was accumulated. The longest running sample achieved a time-to-rupture of more than 45,000 h. Creep testing revealed that the use of undermatching weld metal led to a premature fracture in the weld metal at higher stress levels. Compared with undermatching weld metal, the use of matching and overmatching filler materials increased the time-to-rupture at high stress levels by 75% and 33% at lowest stress levels. At typical component stresses below 100 MPa, all samples failed in the grain-refined heat-affected zone by characteristic type IV failure. For investigations of the failure modes, cross sections of fractured samples were investigated by optical light microscopy, scanning electron microscopy, and electron backscatter diffraction. The mechanism of weld metal creep failures and type IV creep failures is discussed in detail
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Formation of delta ferrite in 9 wt.% Cr steel investigated by in-situ X-ray diffraction using synchrotron radiation
Get PDFIn-situ X-ray diffraction (XRD) measurements using high energy synchrotron radiation were performed to monitor in real time the formation of delta ferrite in a martensitic 9 wt pct chromium steel under simulated weld thermal cycles. Volume fractions of martensite, austenite, and delta ferrite were measured as a function of temperature at a 10 K/s heating rate to 1573 K (1300 °C) and subsequent cooling. At the peak temperature, the delta ferrite concentration rose to 19 pct, of which 17 pct transformed back to austenite on subsequent cooling.Max Kade Foundation, Inc.Austrian Academy of SciencesUnited States. Dept. of Energy (Division of Materials Sciences and Engineering, Office of Science, and Office of Basic Energy Sciences
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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