Development of tomographic reconstruction methods in materials science with focus on advanced scanning methods

Techniques for obtaining 3 dimensional information of individual crystals, socalled grains, in polycrystalline materials are important within the field of materials science for understanding and modeling the behavior of materials.In the last decade, a number of nondestructive X-ray diffraction techniques have been developed, which basically group into two classes: imaging techniques and scanning techniques each having their advantages and drawbacks.

The imaging techniques have fast acquisition times but have reached the limit in resolution and the scanning techniques suffer from slow acquisition times. The purpose of this PhD-project is to develop and implement a new technique, the Boxscan technique, which positions itself between imaging and scanning techniques.

The Boxscan technique bases its spatial information on a scanning approach but uses extended linebeams known from the imaging techniques. Combining this with a novel 6-dimensional indexing routine it is possible to determine grain centers, radii and orientations of hundreds of individual grains in a sample.

The grain centers are found with a precision which is better than the stepping size, and thus provides a road towards future non-destructive 3D studies of nanomaterials. It is furthermore shown that the Boxscan technique can be extended to provide full 3D grain maps by using either Laguerre tessellations or iterative reconstruction methods such as e.g. the algebraic reconstruction technique (ART).

A 3D grain map of a meta-stable beta titanium alloy comprising 1265 grains has been produced as part of a collaboration on spatial resolved strain measurements with Cornell University, USA, and the Advanced Photon Source, USA.