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Microstructure evolution and mechanical response of a boron-modified Ti-6Al-4V alloy during high-pressure torsion processing
Get PDFResearch was conducted on the microstructural evolution and ensuing mechanical response from high-pressure torsion (HPT) processing of Ti-6Al-4V alloy in the as-cast and β-forged conditions with and without 0.1 wt.% boron addition. The boron addition produces refinement of the prior β grains and the (α+β) colonies and introduces an additional TiB phase but this affects the deformation response and the microstructural evolution only at low strains of 0.5 to 5 rotations. In the initial condition the orientation of the (α+β) colonies significantly affects the deformation response and leads to differences in substructure formation in both the as-cast and β-forged conditions. This orientation dependence counts on the initial microstructural differences between the unmodified and the boron modified alloys. At higher strains, there is a similar deformation response and microstructure evolution all the alloys. The hardness variation with equivalent strain is similar for the unmodified and boron modified alloys in as-cast and β-forged conditions and represents various deformation regimes in HPT-processing. Strength modelling confirms a simultaneous contribution from microstructural refinement and increased dislocation density towards the hardness increment during HPT processing. Overall, the as-cast and β-forged Ti-6Al-4V-0.1B alloys possess identical deformation response to the β-forged unmodified Ti-6Al-4V alloy in the initial and intermediate stages. At high levels of straining, all alloys respond in an equivalent manner, thus ruling out any possible effects from additional TiB phase or microstructural refinement for the boron-modified alloys
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
Role Of Boron On The Evolution Of Microstructure And Texture In Ti-6AL-4V-0.1B Alloy
Get PDFTitanium and its alloys constitute an important class of materials for aerospace, biomedical, and chemical industries, primarily due to their high specific strength and fracture toughness with good corrosion resistance. Owing to their hexagonal crystal structure at room temperature, both microstructure and texture play a crucial role in the processing and hence the properties of titanium alloys. The basis for tailoring the microstructure and texture in titanium alloys centers around the transformation of high temperature β (body-centered cubic) to the low temperature α (hexagonal close packed) phase. One of the most widely used titanium alloy is Ti-6Al-4V, which exists as two phase (α+β) alloy at room temperature. The cast structure of the alloy Ti-6Al-4V is generally coarse and has strong solidification texture that leads to inferior properties.
Recently, trace boron addition has been reported to produce substantial refinement in cast microstructure for Ti-6Al-4V. Significant improvements in some of the mechanical properties have been reported for the Ti-6Al-4V-0.1B alloy in the as-cast condition. The reasons for microstructural refinement in the boron modified alloy and associated improvements in properties, however, needs to be investigated since the property attributes strongly depend on finer microstructural details including crystallographic texture. In addition, the titanium alloys are processed through thermo-mechanical treatments that involve deformation and annealing response of the alloy. The effect of boron modification on the processing response during thermo-mechanical treatments (TMP) has also not been studied. All these aspects shape the framework of the thesis, wherein microstructure and texture evolution is probed from starting cast condition through different stages of TMP. Micro-mechanisms are identified at every stage from the interrelation of these two intrinsic factors.
In the first part of the study, the spatial variation of microstructure and texture in the cast ingot has been studied using SEM-EBSD technique. It has been found that trace boron addition (0.1 wt%) to Ti-6Al-4V alloy ensures excellent microstructural homogeneity throughout the cast ingot. A subdued thermal gradient due to constitutional undercooling persists during solidification and maintains equivalent β grain growth kinetics at different locations in the ingot. For Ti-6Al-4V-0.1B alloy, both high temperature β and room temperature α phase textures weaken. The microstructural attributes of boron addition manifests as the absence of grain boundary α-phase and the presence of TiB particles. Both these features strongly affect the mechanism of β→α phase transformation and consequently weaken the α phase texture.
The evolution of microstructure and texture during β-processing of Ti-6Al-4V-0.1B alloy is examined in the second part of the work. Boron modified alloy shows the typical features of β worked microstructure with fine prior β grains, however without the formation of shear bands, which is generally observed in the microstructure of β worked Ti-6Al-4V alloy. The transformed α texture is almost same for the two alloys indicating similarity in the transformation behaviour of boron modified and boron free Ti-6Al-4V alloy due to complete dynamic recrystallization during β processing. The microstructural features as well as the crystallographic texture indicates dominant grain boundary sliding for the boron added alloy which leads to homogeneous deformation response without instability (shear band) formation.
In the third part of the study, the deformation response in the (α+β) regime has been studied by carrying out hot compression tests at different temperature under constant true strain rate to simulate experimental processing conditions for the cast Ti-6Al-4V-0.1B alloy. The critical combinations of temperature and strain rate suitable for processing are identified based on flow curves and kinetic analyses. Microstructural features display dynamic recovery of the α-phase at low temperatures and softening due to globularization and/or dynamic recrystallization at high temperatures irrespective of boron addition. The transition temperature for the two mechanisms is comparatively lower for boron added alloy. Unlike Ti-6Al-4V, no sign of instability formation has been observed in Ti-6Al-4V-0.1B. The absence of macroscopic instabilities and early initiation of softening mechanisms has been attributed to microstructural features and texture of boron modified alloy in the initial as-cast condition.
In the fourth part, the large strain deformation response has been studied for the Ti-6Al-4V-0.1B alloy by rolling in the (α+β) regime. Microstructure in near α rolling regime is characterized by a few kinked and bent α colonies while others are elongated along the rolling direction. Dynamic softening at higher temperatures is more dominant for the boron added alloy. Microstructural features are strongly orientation sensitive while relative differences are inherited from the starting cast alloys. Texture evolution, however, does not markedly vary for the two alloys and indicates little difference in the slip based deformation processes under plane strain condition. The influence of transformation texture appears early for the boron added alloy and affects the final texture in much stronger way at higher temperature. Subsequent to the (α+β) rolling, static annealing of warm rolled alloys has been carried out. A faster annealing kinetics for boron added alloy has been observed, which is related to deformation prior to annealing leading to additional diffusion pathways due to microstructural factors. Texture of the annealed material is similar to the deformed state for shorter annealing times but substantially modifies by epitaxial growth of primary α phase during long time annealing.
The final part of the work deals with the deformation response of boron added alloy under superplastic conditions. Out of the two alloys with similar microstructure and texture, higher elongation for boron modified alloy is justified by the absence of slip based deformation and improved grain boundary sliding. Increase in α/β interfaces due to globularization during warm rolling and static annealing contribute to the grain boundary sliding.
The outcomes of the thesis have been presented as a summary at the end and suggestions have been made indicating the scope for future investigations pertaining to this area
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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