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UCL - Pr. Barnett - Twinning in magnesium alloys II - Controlling Twinning

Le Mercredi 22 Octobre 2008 de 16h15 à 18h15
Dear colleagues,

We are very pleased to invite you to a series of seminars given by Prof. M. Barnett from Deakin University, Australia.  Prof. Barnett is an expert in the analysis of deformation structures in metallic alloys, as many of you know.  He is currently an invited professor at the Ecole Polytechnique de Louvain, UCL, until the end of this year.

Here is the program

1) wednesday october 15, 16h15, room "BARB 91", UCL, Louvain-la-Neuve 
"Twinning in magnesium alloys I - Impact of Twins on Mechanical Response

2) wednesday october 22, 16h15, room "SUD 08", UCL, Louvain-la-Neuve
Twinning in magnesium alloys II - Controlling Twinning

3) thursday october 23, 16h15, room "SUD 08", UCL, Louvain-la-Neuve
Some aspects of the role of shear in deformation structures

4) monday october 27, 16h15, room "BARB 91", UCL, Louvain-la-Neuve
Dynamic recrystallization

(see the map of LLN attached to this email, the room BARB91 is in the auditorium "Sainte Barbe" next to "Place Sainte Barbe" - and the room SUD08 is in the auditorium "SUD" next to "Place croix du Sud")

An abstract is given below for each of these seminars which will last for typically one hour

We would be very grateful if you could transfer this information to the interested researchers and students, as well as to other colleagues who, you think, might be interested to attend these seminars

Best regards

Pascal J. Jacques, Laurent Delannay, Thomas Pardoen


1. Twinning in Magnesium Alloys I - Impact of Twins on Mechanical Response

Deformation twinning plays a large role in the mechanical behaviour of magnesium alloys. This has been long known from the early single crystal experiments of Schmid and later those of Reed-Hill and colleagues. Polycrystalline tests by Hauser and later by Hosford and colleagues showed that the striking effect of twinning seen in single crystal work holds true for aggregates. The present talk focuses on recent work that shows the importance of this deformation mode in commercial magnesium products. Particular attention is paid to the following issues: mechanical anisotropy, work hardening response, Hall-Petch effects, work softening, flow localization and ductile failure. Some simple analytical constitutive models are presented and note is made of some of the main modelling efforts being carried out around the world.

2. Twinning in Magnesium Alloys II - Controlling Twinning

Mechanical twins play a large role in the distinctive mechanical beahviour of magnesium an its alloys. The present talk considers how to exert engineering control over twinning; enhancing or suppressing it, depending on the need. The following issues are considered: the effect of texture, competition with slip modes (i.e. is <c a> slip in magnesium an important "competitor" for twinning), the origin of the strong effect of grain size on twinning, what determines twinning variant selection and what is the role of second phase particles.

3. Some aspects of the role of shear in deformation structures

The crystallographic rotation that accompanies simple shear is unique in that orientations can readily pass through so called "stable" orientations. This has been nicely described by Toth's work on texture development in initially random aggregates. The present talk applies the idea to single grains and shows that this phenomenon provides a potent mechanism for the generation of intra-granular misorientations. It is shown that this is true both in aluminium and steel. Finally, it is shown that the general tendency of shear localization to generate orientation gradients can explain a very wide range of deformation and recrystallization phenomena in warm worked steels.

4. Dynamic Recrystallization

The dynamic recystallization of metals has been frequently studied and this title has been applied to many different phenomena. This has spawned considerable debate in the literature. The present talk avoids this issue and presents an analysis of the likelihood of new grains being formed during deformation as a consequence of grain boundary migration.  It is assumed that the grain "nucleus" is considerably smaller than its final mean size. A criterion is developed and a wide range of materials are compared to determine their propensity for displaying the mechanism. Finally, its role in magnesium alloys is discussed.

Thomas Pardoen
Université catholique de Louvain
Ecole Polytechnique de Louvain (EPL) - Louvain School of Engineering
& Materials Science and Processes Department
& Research Center in Micro and Nanoscopic Materials and Electronic Devices (CERMIN)

address :       Unité IMAP
                 Réaumur, Place Sainte Barbe 2
                 B-1348 Louvain-la-Neuve

tel. 32 10 472417
fax  32 10 474028
email thomas.pardoen@uclouvain.be

Dernière mise à jour par EDT MAIN Lundi 22 Septembre 2008