Microstructure Characterization

One important task of materials science is to determine the relationship between the microstructure and the resulting properties. The microstructure spans over a length scale from the mm-level down to the atomic level. Microstructural features including grain size, phase development, interfaces, dislocations, and point defects have to be understood to establish microstructure-property relationship.

Transmission electron microscopy (TEM) plays a major role within the techniques used to understand the microstructural parameters which control the behavior of advanced materials. Conventional TEM offers quantitative and qualitative information of the morphology, phase distribution, as well as formation of precipitates. Lattice defects, such as point defects or dislocations, as well as planar defects like staking faults, grain boundaries or antiphase boundaries can be analyzed using TEM techniques in order to correlate the results with the mechanical properties. Therefore it is important to study the interfacial structure down to the atomic scale by using e.g. high-resolution TEM. Of particular interest is which type of interfaces occur in polycrystalline materials and how their structure appears (atomically abrupt, phase transformation sequence, special grain boundaries).

Research activities are numerous. Presently, research is focused on the determination of microstructural constituents and phase quantities of the various types of microstructures in intermetallic titanium aluminide alloys. Another research focus lies on ultrafine-grained alloys produced by severe plastic deformation, e.g. high pressure torsion, in close collaboration with the Erich Schmid Institute, Leoben.

Example of the microstructure of a heat-treated multi-phase titanium alumide alloy: a) bright field contrast shows wo-grains with an ellipsoidal shape (dark grey) uniformly distributed in the ßo-TiAl matrix (light gray), surrounded by yg-TiAl grains (bright); b) high-resolution TEM image of a segment of the interface between wo- and ßo-phases.