124,820 research outputs found
Quench sensitivity of Al-Mg-Si alloys: a model for linear cooling and strengthening
No full textIn this work quench-induced precipitation during continuous cooling of five Al-Mg-Si alloys is studied over a wide range of cooling rates of 0.05 K/min - 2x10^4 K/min using Differential Scanning Calorimetry (DSC), X-ray diffraction, optical microscopy (OM), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and hardness testing. The DSC data shows that the cooling reactions are dominated by a high temperature reaction (typically 500 °C down to 380 °C) and a lower temperature reaction (380 °C down to 250 °C), and the microstructural analysis shows they are Mg2Si phase formation and B’ phase precipitation on dispersoids, respectively. A new, physically-based model is designed to model the precipitation during the quenching as well as the strength after cooling and after subsequent age hardening. After fitting of parameters, the highly efficient model allows to predict accurately the measured quench sensitivity, the volume fractions of quench induced precipitates, enthalpy changes in the quenched sample and hardness value
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Predicting the quench sensitivity of Al-Zn-Mg-Cu alloys: a model for linear cooling and strengthening
No full textIn this work the quench sensitivity of Al-Zn-Mg-Cu alloys is studied through continuous cooling at constant rates of a range of alloys using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and hardness testing. The DSC, TEM and SEM data show that the cooling reactions are dominated by a high temperature reaction (typically ~450 °C down to ~350 °C) due mostly to S-Al2CuMg phase formation, a medium temperature reaction (~350 °C down to ~250 °C) due predominantly to ?-Mg(Al,Cu,Zn)2 phase formation and a lower temperature reaction (~250 °C down to ~150 °C) due to a Zn-Cu rich thin plate phase. A new, physically-based model is constructed to predict rates of all reactions, enthalpy changes and resulting yield strength in the artificially aged condition. The model incorporates a recently derived model for diffusion-controlled reactions based on the extended volume fraction concept as well as recent findings from first principles modelling of enthalpies of the relevant phases. The model shows a near perfect correspondence with data on all 6 alloys studied extensively by cooling DSC and hardness testing, and allows prediction of the influence of the 3 major elements and 3 dispersoid forming elements on quench sensitivity
Differential scanning calorimetry as a powerful tool for investigation of solid-phase transformations in heating, isothermal annealing and cooling
No full textSolid-solid phase transformations play an important role for the adjustment of machining- and application-properties of metallic materials. During recent years, we developed advanced techniques to analyze solid-solid phase transformation by DSC in a very wide dynamic range. This talk will introduce these techniques, using reactions in aluminium alloys as examples. To achieve the required high dynamic range during cooling we combine three different indirect and direct measuring techniques and five types of DSC devices. Nowadays physically-based models verified with our DSC results moreover allow to predict precipitation volume fractions, solute mass fractions. Latest results on property predictions as function of cooling rate will be presented
Quench-induced precipitates in Al-Si alloys: calorimetric determination of solute content and characterisation of microstructure
No full textThe present study introduces an experimental approach to investigate mechanical properties of well-defined non-equilibrium states of Al-Si alloys during cooling from solution annealing. The precipitation behaviour of binary Al-Si alloys during the cooling process has been investigated in a wide cooling rate range (2 K/s-0.0001 K/s) with differential scanning calorimetry (DSC). To access the low cooling rate range close to equilibrium an indirect DSC measurement method is introduced. Based on the enthalpy change measured by DSC a physically-based model for the calculation of remaining solute Si amount as function of temperature and cooling rate is presented. Microstructural analyses via light optical microscopy, scanning electron microscopy, atom probe tomography and X-ray diffraction have been performed to evaluate the introduced model and for information on cooling rate dependent precipitate formation. It was found that quench-induced particles of different morphology are formed during cooling. Thermomechanical analyses on clearly distinct undercooled Al-Si states show that flow stress during cooling is dependent on temperature as well as cooling rate. The mechanical behaviour is therefore influenced by solute Si content and quench-induced precipitate
Pragmatic Case Studies as a Source of Unity in Applied Psychology
No full textTo unify or not to unify applied psychology: that is the question. In this article we review pendulum swings in the historical efforts to answer this question—from a comprehensive, positivist, “top-down,” deductive yes between the 1930s and the early 60s, to a postmodern no since then. A rationale and proposal for a limited, “bottom-up,” inductive yes in applied psychology is then presented, employing a case-based paradigm that integrates both positivist and postmodern themes and components. This paradigm is labeled “pragmatic psychology” and, its specific use of case studies, the “Pragmatic Case Study Method” (“PCS Method”). We call for the creation of peer-reviewed journal-databases of pragmatic case studies as a foundational source of unifying applied knowledge in our discipline. As one example, the potential of the PCS Method for unifying different angles of theoretical regard is illustrated in an area of applied psychology, psychotherapy, via the case of Mrs. B. The article then turns to the broader historical and epistemological arguments for the unifying nature of the PCS Method in both applied and basic psychology.Peer reviewe
Dr. Edwin Wright Collection: Author Unknown
No full textNotes - The author relates several short stories about his neighbours including Alex McDonell, homesteading and life around Meanook and Athabasca (1 page
Quantitative analysis of quench sensitivity of 7xxx alloys by using small angle X-ray scattering
No full textDifferent quench sensitivity behaviours for aluminium alloys 7150, 7055, 7085 and 7037 have been systematically studied by using small angle X-ray scattering (SAXS) at the Australian synchrotron. The results have shown that due to different chemical compositions, the ageing behaviour is different after different cooling paths from the solution treatment temperature. The size of ?' precipitates formed during ageing generally decreases with increasing cooling rates. The volume fraction of ?' precipitates formed during ageing increase with increasing cooling rate, indicating that more solute atoms has been retained in solution prior to ageing. For all the studied alloys, no ?' precipitates can be detected below a certain cooling rate, demonstrating that the matrix concentration is not sufficiently high for ?' precipitation during subsequent ageing. The current paper demonstrates that the SAXS technique can be used to quantitatively analyse the effect of quench rate on the size and volume fraction of ?' precipitates in 7xxx alloys in the T6 condition. Moreover, the matrix concentration and/or the chemical composition of ?' precipitates can also be characterised
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