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Scientific Events

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MPIE Colloquium

13560 1523516249

High Temperature Materials - Recent Developments for Future Challenges

The introduction of the talk provides an overview on materials research in IEK-2 (Institute for Energy and Climate Research, Materials Characterization) in Forschungszentrum Jülich. Selected examples of metallic and ceramic high performance materials for applications in energy conversion and storage systems are introduced, e.g. new materials for membranes, coatings or turbine blades. The main part of the presentation focuses on recent developments of novel high temperature Mo‑Si‑B materials, which are potential candidates to substitute Ni-base superalloys in power plants or aircraft turbines. Such alloys include a Mo solid solution phase as well as silicides, which are creep and oxidation resistant, but very brittle phases. The challenge is to balance the properties at ambient temperatures and high temperatures to tailor these multi-phase alloys for the use in a wide temperature range up to 1200°C and various mechanical loads. Concepts of material design, i.e. alloying strategy and process-microstructure-properties relationships are presented in terms of improved mechanical properties and oxidation resistance. The effect of additional elements on the mechanical properties, like fracture toughness, ductile-brittle-transition and creep resistance will be described. The presentation also includes the formation of isotropic and anisotropic microstructures by powder metallurgy, directional solidification and additive manufacturing. The latter process is quite challenging due to ultra-high melting temperatures of >2000°C and corresponding difficulties during melting and rapid cooling. [more]

MPIE Colloquium

12953 1519312993

Nanoindentation for Investigating Dynamics of Shear Bands in Metallic Glasses

Deformation in metallic glasses occurs by initiation and propagation of multiple thin shear bands. This mode is rather difficult to analyse since generally, a single band soon propagates to a large extent in the specimen leading to a catastrophic failure. Exceptions are for example in creep tests under very low stress and moderate temperature or in confined deformation tests. We used instrumented nano-indentations to perform series of independent experiments at room temperature on a Mg65Cu12.5Ni12.5(Ce75La25)10 metallic glass. Loading part of the curves shows serrations which size and duration were measured using an automatic procedure. To make analyses consistent, data were considered only in the domain with similar strain rates, in the range of 1 to 0.3 s-1. Times between successive serrations follow a normal distribution characterizing a random occurrence of deformation burst in the glass. It was then conjectured, first that serration occurs through activation of appropriate zone in the glass that should naturally scale with a multiple of an elementary domain size characterizing the deformation mechanism. Second, as activated zones leading to serration are very few in the glass, the model should be described by the Poisson statistics. Data analyses reveals that serration size are well fitted by a Poisson distribution. The model predict an elementary size which scale with that of the activation volume of 3 atoms, measured from creep test at constant load in the same series of experiments. Eventually, energy dissipated during serration is analyzed as to define shear bands dynamics characteristics.Depending on time, I shall present the use of nano-indention for investigating dynamics of nanoporous metallic materials deformation. N. Thurieau, L. Perriere, M. Laurent-Brocq, Y. Champion, J. Appl. Phys., 118 (2015) 204302. [more]

Mechanism of Enhanced Ductility in Mg Alloys

12983 1519115173

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

12681 1517215921

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]

Atomistic modeling of grain boundary segregation in transition metals

11840 1518598215

Atomistic modeling of grain boundary segregation in transition metals

[more]

11010 1504763231

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

13265 1520518403

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

[more]

 
https://www.mpie.de/events/2768772?page=5
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