Bienvenue sur le site internet du laboratoire LEM3
Actualités au 1/08/2014
Soutenance de thèse de Bo YANG
* 1 août 2014 - Room 426, Zhixing building, Northeastern University, Shenyang, China

Soutenance de thèse de Bo YANG

« Fabrication and crystallographic features of epitaxial NiMnGa ferromagnetic shape memory alloy thin films »

In the present work, epitaxial Ni-Mn-Ga thin films were successfully fabricated on MgO substrate by DC magnetron sputtering. The microstructure, phase constituent, crystal structure and crystallographic features of the phases in NiMnGa thin films were investigated by combination of XRD and SEM-EBSD. Based on the local crystallographic orientation acquired by EBSD, the orientation relationships between martensite variants and their interface planes in NiMnGa thin films were fully revealed through crystallographic analyses. According to the crystallographic determined orientation and theoretical calculation, the martensitic transformation sequence is A?7M?NM. The impact of the transformation crystallographic characters together with the specific constrain of the substrate on the microstructure features of the films is fully depicted. The present study intends to offer deep insights into the crystallographic features and martensitic transformation of epitaxial NiMnGa thin films.

Spécialité : Sciences des matériaux
Ecole doctorale : EMMA

Directeur : Claude ESLING (Prof. UL)
Co-encadrants : Liang ZUO (Univ. of Shenyang, Chine), Yudong ZHANG

Workshop "Steer your career" for PhDs
* 24 juillet 2014, University of the Saarland, Saarbrücken, Building A4 2, Room 2.11.1

The workshop will be hosted by Bérénice Kimpe.

The number of participants is limited to 16. To register, please visit our website.

If you have any questions, do not hesitate to contact me (French, German, English):
Dr. Cecile Dufloux Frankreichzentrum Campus, Geb A4 2 D-66123 Saarbrücken

Séminaire LabEx DAMAS par le Dr. Jian WANG
* 21 juillet 2014 à 14h Salle Klepaczko, Ile du Saulcy, Metz

Le Dr Jian Wang de Materials Science and Technology Division, Los Alamos National Laboratory fera un séminaire intitulé
« Nucleation, Propagation and Interactions of Deformation Twins in Hexagonal-close-packed Metals »

Deformation twinning is a major mode of plastic deformation in hexagonal-close-packed crystals and exhibits more complex nucleation and propagation mechanisms than those in cubic structure. In this lecture, I highlighted several twinning-associated boundaries that play crucial roles in nucleation, growth, and interactions of deformation twins in hcp metals. According to microscopic characterizations and atomistic simulations, four types of boundaries are reviewed including (1) symmetrical tile grain boundaries (SCTGs) that favor twin nucleation or migrate based on twin dislocations, (2) prismatic-basal boundaries (PBs or BPs) associated with twin nucleation via pure-shuffle mechanism, (3) serrated coherent twin boundaries (SCTBs) associated with migration of twin boundaries via glide and climb of twinning dislocations, and (4) prismatic-prismatic (PPs) and basal-basal (BBs) boundaries associated with co-zone twin-twin interactions. More importantly, these boundaries affect twinning and detwinning processes that may correspond to twinning-induced hardening and seem universal associated with twins in hexagonal-close-packed metals. These findings provide theoretical base for researchers to revisit experimental data, rebuild the frame of twinning mechanisms including nucleation and propagation of twins, and advance the development of materials modeling tools at meso- and macro- scales as well as alloy design.

Séminaire Equipe APLI par Tatiana LEBEDKINA
* 17 juillet 2014 à 14h Salle Klepaczko, Ile du Saulcy, Metz

« Effect of equal channel angular pressing on the Portevin-Le Chatelier effect in an Al3Mg alloy »

Plastic deformation of alloys is often accompanied with discontinuous flow known as the Portevin-Le Chatelier (PLC) instability. Due to plastic strain localization in deformation bands, it has a detrimental effect on the material formability. It is of interest to investigate the manifestations of the PLC effect in ultra-fine grained (UFG) materials. Recent studies revealed a large variety of forms the PLC phenomenon takes as a result of grain refinement. Although it could be concluded that the strain interval where the PLC effect occurs is reduced in UFG samples, both a decrease and an increase in the magnitude of serrations on the stress-strain curves was observed. Furthermore, the morphology of stress serrations often displayed substantial changes. In the present work, deformation curves of an Al3Mg alloy processed by equal channel angular pressing (ECAP) are compared with those obtained for the initial coarse-grained material, in a wide strain-rate range covering the main types of behaviour associated with the PLC effect. The microstructure of the UFG alloy is characterized by TEM. It is shown that grain refinement may suppress the PLC instability. To characterize the stress serrations on various time and size scales, statistical and multifractal approaches to the analysis of time series are applied.

Séminaire LabEx DAMAS
par Benoît MALARD
Les Sciences sur la Place
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