Yasmin Ahmed Salem, M.A.
Yasmin Ahmed Salem
Press and Public Relations Officer
Phone: +49 211 6792 722
Room: 222

Scientific Events

Scientific Events


11332 1508915187

Application of Scientific Principles to Aluminium Automotive Sheet

Abstract Aluminium has been used in the manufacture of automobiles for more than 100 years and current usage averages more than 150kg per vehicle. Recent demands for higher fuel economy, improved vehicle performance, and lower CO2 emissions are currently driving a dramatic increase in the usage of specially designed aluminium alloys in the automotive industry. Aluminium flat-rolled sheet products are currently seeing wide-spread application for many components previously produced from steel. The technical requirements for aluminium sheet include high levels of formability, high strength, corrosion resistance, surface appearance, and long term reliability of joints. While these requirements are often in direct conflict, improved understanding of microstructure and surface has enabled the economical production of sheet that can meet the necessary customer demands. Three key developments in metallurgy and surface science that have made aluminium automotive sheet possible are reviewed: control of precipitate morphology for high strength, surface microstructure for bond durability, and crystallographic texture for surface appearance after forming. [more]

11334 1508916120

Shear bands in metallic glasses: what are they, how to find them?

The plastic deformation in metallic glasses proceeds through the activation and sliding of shear bands (SBs). A better plasticity in metallic glasses can be achieved through the enhancement of SB stability and proliferation. Therefore, efforts have been made to understand the true nature of SBs in metallic glasses. However, direct measurements on SBs are limited due to the small width of a shear band (few tenths of nanometers) and the lack of resolution at the atomic scale. In this context, atom probe tomography could bring some missing information about SBs.In the first part of the talk, I present the current state of knowledge on shear bands in metallic glasses. I give information concerning the commonly accepted formation, nature and location of shear bands. In the second part of the talk, I present my own results with Pd- and Pt-based bulk metallic glasses (BMGs) samples deformed by High-Pressure Torsion. HR-TEM and DSC measurements indicate some changes in the short-range order of the samples. The importance of pre-existing SB spacing on the mechanical response during nanoindentation measurements is also presented. The influence of residual stresses on SB proliferation around indenter imprint is shown. Finally, we show the possibility of a phase separation in amorphous Au-based metallic glass thin films and Zr-based BMGs. Atom probe tomography could also be used to confirm the presence of multiple amorphous phases. [more]

Diffusion and segregation of solutes in grain boundaries: from pure metals to high-entropy alloys

MPIE Colloquium

11145 1506515863

Phase-field Modeling of Polycrystalline Structures: From Needle Crystals to Spherulites Phase-field Modeling of Polycrystalline Structures: From Needle Crystals to Spherulites

Results in modeling complex polycrystalline structures by phase-field models that monitor the local crystallographic by scalar or vector orientation fields will be reviewed. The applied models incorporate homogeneous and heterogeneous nucleation of growth centers, and several mechanisms to form new grains at the perimeter of growing crystals, a phenomenon termed growth front nucleation. Examples for PF modeling of such complex polycrystalline structures are shown as impinging symmetric dendrites, polycrystalline growth forms (ranging from disordered dendrites to spherulitic patterns), and various eutectic structures, including spiraling two-phase dendrites. Simulations exploring possible control of solidification patterns in thin films via external fields, confined geometry, particle additives, scratching/piercing the films, etc. are also displayed. Advantages, problems, and possible solutions associated with quantitative PF simulations are discussed briefly. [more]

11333 1508915638

Variational Methods in Material Modeling: Applications of Hamilton’s Principle

The aim of modern material modeling is the realistic prediction of the behavior of materials and construction parts by numerical simulation. Experimental investigations prove that the microstructure and thus the mechanical properties may vary under loads. It is thus essential to describe the load-dependent microstructure in these cases by material models to close the system of fundamental physical equations. One elegant way for the derivation of such material models is given by the Hamilton principle which belongs to the class of variational, energy-based modeling strategies. The talk starts with fundamental investigations for modeling the simple harmonic oscillator. Afterwards, the presented modeling concept is generalized to the Hamilton principle which is also applicable to deformable solids with evolving microstructure. As first example for such materials, phase transformations in solids are modeled. The numerical results are compared to experimental observations and an industrially relevant application is presented. In the last part of the talk, the universal character of the Hamilton principle is demonstrated by solving the inverse problem of topology optimization. To this end, a growth approach as observed in biological processes is presented which computes component structures with minimal weight at maximum stiffness. [more]

International conference “Intermetallics 2017”

17707 1551253876

International conference “Intermetallics 2017”

10985 1504536067

Complex multicomponent alloys: coupled structural and mechanical study of a bcc model alloy, and possible improvement path

A lot of research effort has now been dedicated to the study of complex multicomponent alloys (more commonly called High Entropy Alloys HEA). This family of materials introduced in 2004 breaks with the traditional alloying concept, since they explore the domain of concentrated solid solution(s) of +5 elements. Several studies sprovide fundamental understanding on the structure and the mechanical properties of some of these alloys, mostly fcc [1–3]. If the results are promising, as for example the incredible fracture toughness of FeCoCrMnNi at low temperatures [4], recent papers suggest that equiatomic fcc alloys with less than 5 elements, or non-equiatomic fcc concentrated alloys also display great, or even greater mechanical properties [2,5,6]. The sub-family of bcc complex multicomponent alloys has been less investigated. Therefore, a multi-scale characterization of a model bcc multicomponent alloy with composition Ti20Zr20Hf20Nb20Ta20 is performed. After optimization of the microstructure, investigated by SEM (EBSD), TEM and EXAFS, the mechanical properties of the alloy are studied during both tensile/relaxations tests and shear tests. Deformation mechanisms are discussed in terms of activation volume and flow stress partitioning, interpreted with the help of microstructural investigations by transmission electron microscopy. Finally, the “HEA” concept is coupled with the chemical design based on electronic parameters Bo and Md used in Ti-alloys. This concept, first introduced by Morigana was successfully used to help predicting the structure stability, and hence the mechanical behavior – dislocation glide, twinning induced plasticity (TWIP) or transformation induced plasticity (TRIP) – of Ti-rich alloys [7,8]. The studied composition Ti35Zr27.5Hf27.5Nb5Ta5 displays a large ductility of 20% and an increased work-hardening [9]. It confirms that extending the concept of “HEAs” to non-equiatomic compositions can be highly beneficial and that the design strategy developed for Ti-alloys can be used with great results in concentrated alloys. [1] F. Otto, A. Dlouhý, C. Somsen, H. Bei, G. Eggeler, E.P. George, The influences of temperature and microstructure on the tensile properties of a CoCrFeMnNi high-entropy alloy, Acta Mater. 61 (2013) 5743–5755. doi: [2] Z. Wu, H. Bei, G.M. Pharr, E.P. George, Temperature dependence of the mechanical properties of equiatomic solid solution alloys with face-centered cubic crystal structures, Acta Mater. 81 (2014) 428–441. doi: [3] C. Varvenne, A. Luque, W.A. Curtin, Theory of strengthening in fcc high entropy alloys, Acta Mater. 118 (2016) 164–176. doi: [4] B. Gludovatz, A. Hohenwarter, D. Catoor, E.H. Chang, E.P. George, R.O. Ritchie, A fracture-resistant high-entropy alloy for cryogenic applications, Science. 345 (2014) 1153–1158. doi:10.1126/science.1254581. [5] Y. Deng, C.C. Tasan, K.G. Pradeep, H. Springer, A. Kostka, D. Raabe, Design of a twinning-induced plasticity high entropy alloy, Acta Mater. 94 (2015) 124–133. doi:10.1016/j.actamat.2015.04.014. [6] Z. Li, K.G. Pradeep, Y. Deng, D. Raabe, C.C. Tasan, Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off, Nature. advance online publication (2016). [7] M. Abdel-Hady, K. Hinoshita, M. Morinaga, General approach to phase stability and elastic properties of β-type Ti-alloys using electronic parameters, Scr. Mater. 55 (2006) 477–480. doi: [8] M. Marteleur, F. Sun, T. Gloriant, P. Vermaut, P.J. Jacques, F. Prima, On the design of new β-metastable titanium alloys with improved work hardening rate thanks to simultaneous TRIP and TWIP effects, Scr. Mater. 66 (2012) 749–752. doi: [9] L. Lilensten, J.-P. Couzinié, J. Bourgon, L. Perrière, G. Dirras, F. Prima, I. Guillot, Design and tensile properties of a bcc Ti-rich high-entropy alloy with transformation-induced plasticity, Mater. Res. Lett. 5 (2017) 110–116. doi:10.1080/21663831.2016.1221861. [more]

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