"We are now able to see in-situ the full three dimensional shape of a single grain as it evolves during recrystallization in the interior of a sample," says Soeren Schimdt of the Riso National Laboratory in Denmark. "One could say that we have a full four dimensional (4D) description of the grain. This is the first time ever this has been obtained."

The four-dimensional microscope is a modified version of the Three Dimensional X-Ray Diffraction (3DXRD) microscope at the European Synchrotron Radiation Facility (ESRF) in Grenoble. Schimdt and colleagues from Riso and the ESRF used a beam of 50 keV X-rays from the ESRF to study a single crystal of aluminium that had been deformed enough to ensure that recrystallization would occur.

The Danish scientists started by positioning their sample in the 3DXRD microscope so that the X-ray beam intersected a single recrystallizing grain. Next, they made a series of vertical cuts across the grain and took images of the successive cross-sections. By then stacking these images together, they were able to obtain a full three-dimensional image of the grain. The procedure was repeated several times to produce a movie of the process (see Related links).

The team now plans to investigate recrystallization in other situations. "Hopefully we can combine these results and come up with a more fundamental description of the recrystallization process," says Schmidt.