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Yasmin Ahmed Salem
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Scientific Events

Scientific Events

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Mechanism of Enhanced Ductility in Mg Alloys

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Mechanism of Enhanced Ductility in Mg Alloys

Pure Mg has low ductility due to strong plastic anisotropy and due to a transition of <c+a> pyramidaldislocations to a sessile basal-oriented structure [1]. Alloying generally improves ductility; for instance, Mg-3wt.%RE (RE=Y, Tb, Dy, Ho, Er) alloys show relatively high ductility [2], and typically larger than mostcommercial Mg-Al-Zn alloys at similar grain sizes. Possible concepts for ductility in alloys include thereduction of plastic anisotropy due to solute strengthening of basal slip, the nucleation of <c+a> from basal I1stacking faults, the prevention of the detrimental <c+a> transformation to sessile structures, and the weakeningof strong basal texture by some solute/particle mechanisms. Here, we introduce a new mechanism ofpyramidal cross-slip from the lower-energy Pyr. II plane to the higher energy Pyr. I plane as the key toductility in Mg and alloys [3]. Certain alloying elements reduce the energy difference between Pyr. I and IIscrew dislocations, accelerating cross-slip that then leads to rapid dislocation multiplication and alleviates theeffects of the undesirable pyramidal-to-basal dissocation. A theory for the cross-slip energy barrier ispresented, and first-principles density functional theory (DFT) calculations, following methods in [4], are usedto compute the necessary pyramidal stacking fault energies as a function of solute type for many solutes in thedilute concentration limit. Predictions of the theory then demonstrate why Rare Earth solutes are highlyeffective at very low concentrations, and generally capture the trends in ductility and texture evolution acrossthe full range of Mg alloys studied to date. The new mechanism then points in directions for achievingenhanced ductility across a range of non-RE alloys.[1] Z. Wu, W.A. Curtin, Nature 526 (2015) 62-67[2] S. Sandlobes, et al., Acta Materialia 59 (2011) 429-439; Acta Materialia 70 (2014) 92–104[3] Z. Wu, R. Ahmad, B. Yin, S. Sandlobes, and W. A. Curtin, Science 359, 447-452 (2018).[4] B. Yin, Z. Wu, and W. A. Curtin, Acta Materialia 136 (2017) 249-261. [more]

Early stages of high temperature oxidation and sulphidation studied by synchrotron X-ray diffraction and spectroscopy

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Early stages of high temperature oxidation and sulphidation studied by synchrotron X-ray diffraction and spectroscopy

Ferritic high temperature alloys are widely used as boiler tube and heat exchanger materials in thermal power plants. All technologies have in common that the applied materials are exposed to different temperatures, process pressures and reactive atmospheres which lead to a change of the material properties and a further degradation of the material. Material changes caused by ageing in highly corrosive and toxic gases such as SO2 are mainly studied ex situ after the reaction is finished.The presentation will focus on a novel approach to study high temperature oxidation and sulphidation of alloys aged in a strongly corrosive environment in real time by energy dispersive X-ray diffraction (EDXRD). A special designed corrosion reactor was used to combine high temperature gas corrosion experiments with the collection of diffraction pattern. For this technique high energetic white X-ray radiation (10-100 keV) was used instead of conventional monochromatic radiation. It enables us to study crystallization procedures on short and medium time scales (1 min < t < 24 h) as a function of process time.X-ray diffraction is not phase sensitive for structural very similar oxide phases such as Fe2O3 and Cr2O3. To enlighten the formation mechanism of protective Cr2O3 at high temperature in corrosive atmosphere for different ferritic alloys an experimental setup for X-ray absorption near edge structure spectroscopy (XANES) in corrosive environment was developed and put into operation. The presentation will provide an overview of the possibilities of high temperature corrosion analysis using synchrotron-based X-ray diffraction and spectroscopy techniques. [more]

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"Mechanics meets Energy VI” symposium at Kloster Steinfeld/Eifel

Fundamentals of mechanical response

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"Fundamentals of mechanical response" at the Conference on Electronic and Advanced Materials

Atomistic modeling of grain boundary segregation in transition metals

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Atomistic modeling of grain boundary segregation in transition metals

[more]

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4th NRW-APT User Meeting

The Max-Planck-Institut für Eisenforschung GmbH in Düsseldorf is organizing the 4th NRW-APT user meeting on November the 23rd 2017 and we would like to invite you and your research colleagues to participate in this event. This meeting will bring together scientists from North Rhine-Westphalia dealing with APT technique or correlating APT with other techniques. We want to discuss problems and share knowledge regarding sample preparation, measurement conditions, data reconstruction & analysis, etc. If you and your colleagues would like to attend this event, then please register before November 6th 2017. There are limited places only. We are looking forward to see you in Düsseldorf! [more]

Synthesis and characterization of tungsten-based composites for high-temperature applications

 
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