CEMES – Thursday seminars – From the plate to the atom, or the interest of multi-scale approaches in metallurgy

Metals such as Titanium or Magnesium have the potential to become the materials of the future in many applications (aerospace, automotive, bicycles, electric scooters) where their mechanical strength and lightness are two major assets. The downside is that these metals are not easily shaped, as can be done with aluminium or steel for example. This limition comes from their hexagonal crystal structure, which imposes a limited number of atomic planes on the dislocations (source of malleability) in which they can easily move. To deform a titanium plate, to make a modern art museum in Bilbao for example, several approaches are possible. At the atomic level, we can modify the chemical environment by using alloying elements to make the dislocations more mobile. But one can also intervene at larger scales: at the level of the grains that make up the plate and the way they are arranged, which is an even larger scale. Through this example, we will show how it is necessary to combine so-called "multi-scale" approaches to understand and thus to come up with practical solutions, based on physical metallurgy (characterisations at different scales by electron microscopy, X-rays) to get around the problems of brittleness of Titanium, but also of other hexagonal metals. The Guggenheim Museum in Bilbao, designed by Frank Gehry, is covered with 33,000 titanium plates.