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An evaluative approach to correlate machinability, microstructures, and material properties of gamma titanium aluminides
No full textSeveral generations of gamma titanium aluminides have been developed over time, and they are nowadays commercially available. The differences in chemical composition, as well as the thermal treatments, greatly influence the properties of the alloys. This implies considerable effects on the production process performances. Benchmark trials were performed on three γ-TiAl alloys: Ti–48Al–2Cr–2Nb, Ti–43.5Al–4Nb–1Mo–0.1B, and Ti–45Al–2Nb–2Mn + 0.8 vol.% TiB2 XD, focusing on machinability and material characterization. The extremely dissimilar results obtained when turning and milling can be traced back to the different microstructures, as well as to the alloying elements, factors both affecting the mechanical and thermal material properties
On high-speed turning of a third-generation gamma titanium aluminide
Get PDFGamma titanium aluminides are heat-resistant intermetallic alloys predestined to be employed in components suffering from high mechanical stresses and thermal loads. These materials are regarded as difficult to cut, so this makes process adaptation essential in order to obtain high-quality and defect-free surfaces suitable for aerospace and automotive parts. In this paper, an innovative approach for longitudinal external high-speed turning of a third-generation Ti-45Al-8Nb- 0.2C-0.2B gamma titanium aluminide is presented. The experimental campaign has been executed with different process parameters, tool geometries and lubrication conditions. The results are discussed in terms of surface roughness/integrity, chip morphology, cutting forces and tool wear. Experimental evidence showed that, due to the high cutting speed, the high temperatures reached in the shear zone improve chip formation, so a crack-free surface can be obtained. Furthermore, the use of a cryogenic lubrication system has been identified in order to reduce the huge tool wear, which represents the main drawback when machining gamma titanium aluminides under the chosen process condition
High performance cutting of gamma titanium aluminides: Influence of lubricoolant strategy on tool wear and surface integrity
Get PDFHeat resistant gammatitaniumaluminidesareintermetallicalloysplannedtobewidelyusedinhigh- performanceaircraftengineswithinthenextfewyears.Thisapplicationfieldisascribedtothe exceptionalmaterialproperties,especiallythelowdensityandauniquestrength-to-weightratiofor titanium-basedalloys,goodoxidationbehaviourandthermalstability,limitedductilityandfracture toughnessbelowbrittle-to-ductiletransition,andgoodcreepresistance. The demandingmachinabilityofgammatitaniumaluminidescanbetracedbacktothesedesirable materialproperties.Consequently,cuttingprocessadaptationisessentialtoobtaincomponents suitabletosatisfystrongregulationsregardingsurfaceintegrity,withoutneglectinganeconomical production.Previousresearchactivitiesconfirmedthatthermalmaterialsofteningduringcuttingdue to thehighspeedmachiningisakeytoreachhighqualitysurfaces,buttoolwearwasidentifiedasthe limitingfactor. The relativelyhighcuttingspeedresultsinhightemperaturesintheshearzoneandthelowthermal conductivityofthe g-TiAl workpiecematerialleadstoanextremethermaltoolload.Furthermore,in combinationwiththeformationofsaw-toothchipsandthediscontinuousflowofthechipalongthe rake face,adhesiveweariscaused. The influenceofconventionalfloodcoolingandhighpressurelubricoolantsupply(wetconditions), cryogeniccoolingwithliquidnitrogen,andminimumquantitylubrication(MQL)wereinvestigatedin longitudinalexternalturningoperations.Toolwear,cuttingforces,chipmorphologyandsurface roughnesswereevaluated.Surfaceintegritywasanalysedintermsofmachinedsurfacedefectsand sub-surfacealterations. The investigationsindicatethatcryogeniccoolingisthemostpromisinglubricationstrategy, meaningthatthethermodynamicalimpactoftheexpandingliquidnitrogenapplieddirectlyclose to thecuttingzonesuccessfullycounteractthehugethermalloadonthetoolcuttingedges,providing potentiallyenormousbenefitsintermsoftoolwearreductionandconsequentsurfacequality improvemen
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
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
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