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An atom probe characterization of grain boundaries in an aluminium alloy processed by equal-channel angular pressing
No full textThe segregation of solute elements at the grain boundaries of an Al–Zn–Mg–Cu alloy processed by equal-channel angular pressing was characterised using three-dimensional atom probe tomography. The results show that Mg and Cu segregate strongly to the grain boundaries but Zn shows no clear segregation and even becomes depleted near the boundaries. Trace elements such as Zr, Cr, Si and Mn show no clear segregation at the grain boundaries. An increase in the number of passes leads to a decrease in the grain size but there is no clear effect on the levels of solute segregation at the boundaries. The significant segregation of certain major alloying element at the boundaries of ultrafine-grained alloys implies that the less super-saturation solutes in the matrix will be available for precipitation with a decrease in the average grain siz
Solute segregation on structural defects in an ultrafine-grained Al-Cu-Mg alloy
No full textMicrostructure evolution of an ultrafine-grained Al-Cu-Mg alloy has been studied during and after high-pressure torsion (HPT) at ambient temperature. Hardness distribution in aluminum disks is characterized by micro-Vickers hardness. The ultrafine-grained microstructures after HPT are examined by transmission electron microscopy (TEM), X-ray diffraction and differential scanning calorimetry (DSC). The location, structure and composition of clusters and nanoscale precipitates along lattice defects (dislocations, cell walls or grain boundaries) are clarified by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The microstructure observation reveals grain refinement and dislocations contribute to a significant increase in hardness. Differential scanning calorimetry (DSC) is used to analyze the energy absorption during this stage of hardening. It is found that, during during the DSC after HPT work hardening, a substantial exothermic heat evolution occurs. The source of reaction enthalpy involves dislocation annihilation, the growth of ultrafine grains and grain boundary segregation
Microstructural evolution, strengthening and thermal stability of an ultrafine-grained Al–Cu–Mg alloy
No full textTo gain insight into the origin of the ultra-high strength of ultrafine-grained (UFG) alloys, the solute clustering, precipitation phenomena, and microstructural evolutions were studied in an UFG Al-4.63Cu-1.51 Mg (wt.%) alloy (AA2024) processed by high-pressure torsion (HPT). The thermal analysis was performed using differential scanning calorimetry. The microstructures, internal microstrains and hardness following heating at a constant rate were characterised at room temperature using X-ray diffraction (XRD), transmission electron microscopy (TEM) and atom probe tomography (APT). The microhardness of the HPT processed sample initially increases following heating to 140 °C, and then remains unchanged on further heating to 210 °C. As the temperature increases up to 210 °C, the crystallite size calculated from XRD line broadening remains about 60–70 nm, while the dislocation densities remain in excess of 2 × 10^14 m^2. A multimechanistic model is established to describe the strengthening due to grain refinement, dislocation accumulation, solid solution, precipitation, solute clusters and their segregation. The analysis reveals that solute clusters and lattice defects are key factors in HPT-induced strengthening of alloys, and illustrates the interactions between alloying elements, dislocations and grain boundaries enhance strength and stabilize ultrafine microstructures. Furthermore, for an HPT sample heated beyond 210 °C, the formation of nano-precipitates also contributes to hardness increment. The multimechanistic model for hardness contribution indicates the short-range order strengthening due to cluster-defect complexes is the dominant mechanism, which accounts for more than 40% of overall hardness
Strengthening of an Al-Cu-Mg alloy processed by high-pressure torsion due to clusters, defects and defect-cluster complexes
Get PDFA physically-based model is established to predict the strength of cluster strengthened ultrafine-grained ternary alloys processed by severe plastic deformation. The model incorporates strengthening due to dislocations, grain refinement, co-clusters (due to short range order and modulus strengthening) and solute segregation. The model is applied to predict strengthening in an Al-Cu-Mg alloy processed by high-pressure torsion (HPT). The microstructure was investigated using transmission electron microscopy (TEM), atom probe tomography (APT), and X-ray diffraction (XRD). Analysis of XRD line profile broadening shows that the dislocation density increases significantly due to severe plastic deformation, which contributes to the increase of strength. APT reveals the presence of nanoscale co-clusters and defect-solute clustering. The concepts of the multiple local interaction energies between solutes and dislocations were used to quantitatively explain the strengthening mechanisms. The model shows a good correspondence with measured microstructure data and measured strength
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
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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