Roland Logé | EPFL Graph Search

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Roland Logé is an associate professor at EPFL, with a primary affiliation to the Materials Institute, and a secondary affiliation to the Microengineering Institute.

After graduating in 1994 at UCL (Belgium) in Materials Engineering, he earned a Master of Science in Mechanics in 1995, at UCSB Santa Barbara (USA). He received his PhD at Mines Paristech-CEMEF (France) in 1999, where he specialized in metal forming and associated microstructure evolutions. After a postdoc at Cornell University (USA) between 1999 and 2001, he entered CNRS in France.

In 2008, he was awarded the ALCAN prize from the French Academy of Sciences, together with Yvan Chastel.

In 2009 he became head of the Metallurgy-Structure-Rheology research group at CEMEF.

In 2011, he launched a “Groupement de Recherche” (GDR), funded by CNRS, networking most of the researchers in France involved in recrystallization and grain growth.

In 2013, he became Research Director at CNRS.

In March 2014 he joined EPFL as the head of the Laboratory of Thermomechanical Metallurgy.

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Biography

Roland Logé is an associate professor at EPFL, with a primary affiliation to the Materials Institute, and a secondary affiliation to the Microengineering Institute.

In 2008, he was awarded the ALCAN prize from the French Academy of Sciences, together with Yvan Chastel.

In 2009 he became head of the Metallurgy-Structure-Rheology research group at CEMEF.

In 2011, he launched a “Groupement de Recherche” (GDR), funded by CNRS, networking most of the researchers in France involved in recrystallization and grain growth.

In 2013, he became Research Director at CNRS.

In March 2014 he joined EPFL as the head of the Laboratory of Thermomechanical Metallurgy.

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Finite element method

The finite element method (FEM) is a popular method for numerically solving differential equations arising in engineering and mathematical modeling. Typical problem areas of interest include the tr

Grain boundary

In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are two-dimensional defects in the crystal structure, an

Strain rate

In materials science, strain rate is the change in strain (deformation) of a material with respect to time. The strain rate at some point within the material measures the rate at which the distance

, , , ,

In this work we perform a neutron Bragg edge tomography of stainless steel 316L additive manufacturing samples, one as built via standard laser powder bed fusion, and one using the novel three-dimensional (3D) laser shock peening technique. First, we consider conventional attenuation tomography of the two samples by integrating the signal for neutron wavelengths beyond the last Bragg edge, to analyze the bulk density properties of the material. This is used to map defects, such as porosities or cracks, which yield a lower density. Second, we obtain strain maps for each of the tomography projections by tracking the wavelength of the strongest Bragg edge corresponding to the {111} lattice plane family. Algebraic reconstruction techniques are used to obtain volumetric 3D maps of the strain in the bulk of the samples. It is found that not only the volume of the sample where the shock peening treatment was carried out yields a higher bulk density, but also a deep and remarkable compressive strain region. Finally, the analysis of the Bragg edge heights as a function of the projection angle is used to describe qualitatively crystallographic texture properties of the samples.

AMER PHYSICAL SOC2022

Evolution of deformation twinning mechanisms in magnesium from low to high strain rates

Cyril Cayron, Nicolò Maria Della Ventura, Manish Jain, Roland Logé, Xavier Maeder, Johann Michler, Amit Sharma

We present a systematic investigation of {10 (1) over bar2} extension twinning mechanism in single crystal magnesium micropillars deformed over seven orders of magnitude of strain rate, from 10(-4) to 500 s(-1), revealing how the accommodation of newly formed twins evolves with and depends on the kinetic compatibility of interfacial processes when high deformation rates are imposed. By combination of post-mortem 3D Electron Backscattered Diffraction, Transmission Kikuchi Diffraction and Transmission Electron Microscopy techniques, this work unveils the progressive evolution of the accommodating twin mechanisms from low to high strain rate, correlating differences in mechanical behavior with differences in twin crystallography. Away from quasi-static conditions, simple considerations of twinning shear do not suffice to describe unconventional twin morphologies, requiring the competition between newly activated dislocations and lattice distortions for allowing the evolution of the twin boundary along non-invariant twin planes. Under shock compressions, the basal/prismatic transformation establishing a lattice misorientation of 90 degrees entirely governs the parent -> twin conversion. The results illustrated here confirm that some of the recent interpretations deduced by particular twin morphologies are not universally valid and that deformation twinning is not only stress-but also strongly time-controlled. (C) 2022 The Author(s). Published by Elsevier Ltd.

ELSEVIER SCI LTD2022

Micro-addition of Fe in highly alloyed Cu-Ti alloys to improve both formability and strength

Cyril Cayron, Roland Logé, Baptiste Thomas Jean Rouxel

Cu-Be alloys provide excellent electrical and mechanical properties, but present serious health hazards during manufacturing. Among alternative alloys, the Cu-Ti system has the highest yield strength; however, Ti cannot be easily solutionized at concentrations above 4 wt%, resulting in a relatively low formability. In this study, Cu-xTi-yFe (x = 3, 5, 6 wt% and y = 0, 0.3 wt%) alloys were studied after both solution-annealing and age-hardening through mechanical testing and microstructure analysis. Micro-additions of Fe kept high concentration of Ti in solid solution (up to 6 wt%) after water quenching and suppressed the classical "wave-like" early-stage precipitation. Instead, a new dispersion of nano precipitates was observed. This behavior results in doubling the ductility in the solution annealed state (up to 48% elongation), together with maintaining a very high strength after ageing (up to 975 MPa) from precipitation of metastable nano alpha-Cu4Ti. This study shows that Fe micro-additions, when combined with a higher amounts of Ti (6 wt%), enables the production of Cu-based alloys combining high formability and strength, providing an excellent alternative to Cu-Be in mechanical applications. (C) 2021 Published by Elsevier Ltd.

ELSEVIER SCI LTD2022

MSE-215: Mise en oeuvre des matériaux II

Introduction aux relations mise en œuvre-structures-propriétés des polymères, céramiques et métaux, fournissant les bases nécessaires à la sélection de matériaux et procédés pour la fabrication de composants en microtechnique.

MSE-310: Deformation of materials

Présentation des mécanismes de déformation des matériaux inorganiques: élasticité, plasticité, fluage.

MSE-657: CCMX Winter School - Additive Manufacturing of Metals and the Material Science Behind It

This course is designed to cover a series of important scientific aspects related to the field of additive manufacturing of metals and alloys and to provide an in-depth review of corresponding fundamentals. It features 9 modules consisting of presentations given by lecturers and the participants.