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Press release | Materials | Nuclear energy | Physics
Despite the many similarities between titanium and zirconium, researchers at CEA, CNRS and Université Claude Bernard Lyon 1 have demonstrated that plastic deformation develops differently in these two metals. It is commonly accepted that Ti and Zr should exhibit a similar response to mechanical stress. However, by combining microscopic experimentation and modeling techniques with GENCI and PRACE computing resources, the researchers have identified two different dislocation motions in these materials. Their goal is now to investigate and predict the mechanical properties of various innovative alloys. The results are published in the August 2015 issue of Nature Materials.
Titanium and zirconium, two
crystalline metals used in industrial applications (particularly nuclear and
aeronautical applications), have very similar electronic structures (same
number of electrons in the outer shell). They also crystallize in a similar
manner, i.e. when the atoms assemble into a crystalline structure, they adopt a
Despite the many similarities
between these two metals, the researchers have unexpectedly shown that they
respond differently to mechanical stress. By stretching a pure sample of each
metal under a transmission electron microscope at various temperatures ranging
from -170°C to +20°C, they have managed to observe and compare apparent line
defects, i.e. dislocations evolving as a function of mechanical stress. Two
types of dislocation behavior have been observed: dislocations passing jerkily
through different planes (in the case of titanium), and dislocations slipping
continuously on a single plane (in the case of zirconium).
In order to understand this
difference in dislocation mobility, the researchers have modeled the
dislocation core at the atomic scale using GENCI's Curie supercomputer. These simulations show that the dislocations may
adopt two different configurations: one slipping easily and continuously, the
other with difficulty. Each of these two configurations exists in both
metals, but with a different degree of stability (or recurrence): the most
stable dislocations observed in titanium are of the easily slipping type, as
opposed to zirconium.
With this new understanding of
plasticity in pure titanium and zirconium, it is now possible to model the
plastic deformation behavior of corresponding alloys based on robust physical
principles. Regardless of whether titanium or zirconium alloys are considered,
the alloying elements used (particularly oxygen) have a significant effect on
the material's plastic deformation behavior. The next step is therefore to
investigate how the alloying elements interact with the different dislocation
configurations and modify both their stability and mobility. There are
important technological stakes involved, since zirconium and titanium alloys
are structural materials commonly used in the nuclear and transport industries.
research has benefited from 800 000 hours of computing time on GENCI
computing resources in 2014, and 12 million hours on the Curie supercomputer
from March 2014 to March 2015, within the framework of the PRACE project.
 Implemented at CEA's TGCC high performance computing center
Dislocation locking versus easy glide in titanium and zirconium,
E. Clouet, D. Caillard, N. Chaari, F. Onimus and D. Rodney, Nature Materials
The complete study can be viewed online
CEA is a French government-funded technological research organisation in four main areas: low-carbon energies, defense and security, information technologies and health technologies. A prominent player in the European Research Area, it is involved in setting up collaborative projects with many partners around the world.