1,720,960 research outputs found
Achieving an excellent combination of strength and plasticity in a low carbon steel through dynamic plastic deformation and subsequent annealing
No full textAn investigation was conducted to evaluate the effect of dynamic plastic deformation (DPD) and post-DPD annealing on the microstructural and mechanical properties of a tempered low carbon steel. The results showed that ultrafine-grained structures consisting of elongated martensitic laths and sub-grains are achieved after DPD processing. The amounts and sizes of carbides in the steels, identified as (Fe,Cr,Mn,Mo)
3C, decreased markedly with DPD straining due to their fragmentation and dissolution but a large number of finer carbides appeared due to re-precipitation during subsequent annealing. A simultaneous improvement in the strength and plasticity was obtained at DPD strains below ∼0.8. This increase in strength by ∼30–60% is mainly attributed to grain boundary strengthening, dislocation strengthening while the good plasticity is due to more active sliding systems, a reduction in the stress concentration during loading because of the amount decreasing of M
3C distributed along the interfaces, the increase of crack propagation resistance by more grain boundaries and the energy released through the occurrence of delamination fracture. After post-DPD annealing both the strength and plasticity improved compared with the as-received steel. Strengths higher by ∼20–39% were attributed to a combination of grain boundary strengthening, dislocation strengthening and precipitation strengthening derived from the re-precipitation of fine and dispersed carbides. The dislocation recovery occurring during annealing led to a decrease in strength compared with that before annealing. The incremental increase in plasticity is attributed to a combination of further active slip systems, a decreasing dislocation density and a dispersed distribution of finer carbides.
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Strain rate dependence of compressive behavior in an Al-Zn-Mg alloy processed by ECAP
No full text
Experiments were conducted to study the compressive mechanical properties of an Al-Zn-Mg alloy after solid solution treatment and equal-channel angular pressing (SS-ECAP) using strain rates ranging from 1.0 × 10
−3
to 3.0 × 10
3
s
−1
. The results show that SS-ECAP processing enhances the compressive strength due to the high dislocation density, large numbers of fine precipitates and grain refinement. The alloy in both the peak-aged (as-received) and the SS-ECAP states shows a strain rate strengthening effect such that the strain rate sensitivity increases with increasing strain rate. The high volume fraction of fine precipitates in the SS-ECAP alloy decreases the strain rate sensitivity. The coarse precipitates in the peak-aged alloy are fragmented while their sizes increase in the SS-ECAP alloy due to dynamic precipitation assisted by the high density of dislocations during compressive testing. With increasing strain rate, the size of the precipitates further increases for the SS-ECAP alloy and this is influenced by accelerated dislocation motion. During compression, the T (Al
20
Cu
2
Mn
3
) and E (Al
18
Mg
3
Cr
2
) phases evolve into a new tetragonal phase containing Mg, Mn, Cr and Zn with Al.
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Microstructure and mechanical properties of an Fe–Mn–Al–C lightweight steel after dynamic plastic deformation processing and subsequent aging
No full textAn austenitic low-density steel was processed by dynamic plastic deformation (DPD) over the strain range from 0.25 to 0.75 followed by aging at 450°C and then it was subjected to compressive testing at strain rates of 1.0 × 10-3 − 2.0 × 103 s-1. The results show that fine grain structures with high density dislocations are achieved after DPD processing. After aging, the grain size increased slightly together and there was an additional marginal decrease in the dislocation density. κ-carbides only appeared in the samples after DPD processing at the strain of 0.75 and after subsequent aging. Submicron-sized (Nb, Mo)C particles existed in the matrix before DPD and there was no change in size and distribution during DPD processing and post-DPD aging. The yield strengths of the steels after DPD at different strain rates increased significantly by ~120-190% compared with the as-received sample, where this is mainly due to a combination of dislocation strengthening and grain boundary strengthening. For the steel processed by DPD at strain of 0.75, there was an additional precipitation strengthening of κ-carbides besides the dislocation strengthening and grain boundary strengthening, and this produced an increase of over ~900 MPa in yield strength by comparison with the as-received steel. After aging, the yield strength decreased slightly due to a reduction in the dislocation density and a slight coarsening of the grains, except for samples after DPD at a strain of 0.75 which showed a slight increase in strength due to further κ precipitation. The strain rate strengthening effect and strain hardening ability were also analyzed
An evaluation of the microstructure and microhardness in an Al–Zn–Mg alloy processed by ECAP and post‐ECAP heat treatments
No full textHerein the microstructure evolution and microhardness variations in a peak‐aged Al–Zn–Mg alloy after equal‐channel angular pressing (ECAP) for 1–8 passes followed by heat treatments at temperatures of 393–473 K for 5–20 h are examined. The results show that ECAP processing hardens the alloy, and the hardness increases with each pass due to grain refinement, the formation of large numbers of fine precipitates, and the introduction of a high dislocation density. Post‐ECAP annealing at 393 K up to 20 h after 1 and 4 passes of ECAP leads to a further increase in microhardness and this increase is substantial for an annealing time of 20 h after 1 pass due primarily to the extensive formation of a nano‐sized η′ phase. After ECAP for 8 passes, post‐ECAP annealing at 393 K for 5 h or more leads to softening due to the occurrence of recrystallization and the transformation of fine η′ to coarse η. Post‐ECAP anneals at the higher temperatures of 423 and 473 K are not capable of producing high hardness values
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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