Microstructure Characterization

The microstructure analyses performed at the Chair Metallic Materials range from the characterization with optical microscopy (LM) and the analysis of precipitates and intermetallic phases in a scanning electron microscope (SEM) up to the investigation of distortion mechanisms in a transmission electron microscopy (TEM). The preparation of the specimens for the optical microscopy, SEM and TEM is carried out in the metallographic laboratory.

For  the first characterization of the microstructure an optical microscope of the brand Zeiss Axioskop with a4i-image-analysis as well as microhardness testing system of the type Struers-Duramin is available.

A SEM of the type Jeol 640 is available for further investigations of the microstructure, as for example for the analysis of fracture surfaces or fine surface structures. A built-in Link-EDS-system allows the qualitative and quantitative analysis of the chemical composition of precipitates and intermetallic phases.

The specimens for the TEM investigations are prepared primarily by electrolytic thinning. The final preparation occurs by means of dimple grinder and an ionic-mill (Bal-Tec Res010). The TEM investigations are carried out with a Philips-CM 30 which is equipped with 11 Megapixel CCD camera (Gatan, Orius SC 1000) and a Voyager EDS system for the element analysis. The exact lighting of the specimen permits  the determination of the microstructure and chemical composition  in the submicrometer range. Therefore, it is possible to carry out investigations of dislocation movements in deformed microstructures. In this field a special expertise lies in the characterization of Nickel base super alloys.

Complementary to the electron microskopy at the Chair Metallic Materials different laboratory X-ray diffractometers are available. With these systems analyses of the phase compositions, textures and residual stresses in engineering materials and components can be carried out. As a result of the penetration depth of the radiation of some micrometers X-ray diffractometry delivers information about the area close to the surface zone. The spatial resolution of laboratory scale X-ray diffractometers ranges according to the measuring procedure from approximately 100 mm² up to approximately 10 mm². 

The findings of these investigations are required for the validation of the results of the simulations accompanying the extrusion as well as for the interpretation of the macroscopic mechanical-technological properties and characteristic of the extrusion products. by the extensive knowledge of the microstructure and their correlation with the mechanical properties it is possible to optimize these by a defined alteration of the process parameters already during the extrusion process. 

To be able to respond to the large variety of technological questions, the X-ray diffractometers which are available at the Chair Metallic Materials, are differently equipped. Thus X-ray diffractometers equipped with scintillation and position-sensitive detectors as well as with furnaces for investigations at elevated temperatures are available.

In addition to the available laboratory X-ray diffraction systems synchrotron X-ray sources such as  BESSY in Berlin, HASYLAB in Hamburg and ESRF in Grenoble are frequently used.