Volume 55, Issue 7

Research and development projects on materials for applications exposed to high temperatures and radiation include comprehensive mechanical and metallographic examinations as well as analysis methods based on electron microscopy investigations using SEM (scanning electron microscope) and TEM (transmission electron microscope). In addition to 2D EDS and EBSD analyses in the μm range, the imaging 3D analysis method has become more and more important in the past few years. Particularly, the combination of SEM images with simultaneously obtained EDS and EBSD data during 3D analyses is a test method which complements previous material testing and produces clear results since much larger data sets are used in order to determine the composition of a material and the phases present in its microstructure. Since 2014, our institute has been working with a workstation (FIB/SEM) from the company Zeiss, a crossbeam AURIGA 40 with 3D analysis. This paper will present unparalleled results of the investigations carried out on the structural and high-temperature material 12Cr0.36Ta steel, nanocrystalline tungsten and intermetallic NiAl-Cr alloys using the above-mentioned 3D technique.

The aim of this study was the morphological optimization of graphite by generating knowledge able to determine which metallurgical manufacturing factors have a significant influence on the geometry of the graphite precipitated in spheroidal grey cast irons with a mass coefficient of 4, used in the manufacture of wind turbine hubs. The research study was conducted on an industrial scale applying a fractional Design of Experiments (DoE) with 7 factors, 16 experiments and resolution IV. The following constitute the most noteworthy novel results obtained in the study. The effect of La on the graphite “counts” is strengthened by pre-inoculation of the molten iron bath with SiC. Furthermore, graphite counts can be increased under low carbon equivalent conditions using post-inoculants containing Zr. Finally, high values of Mn lead to a reduction in the size of the precipitated graphite.

Pipes made of stainless steel in the drinking water supply system showed pitting corrosion in the heat-affected zone (HAZ) of the welded joints. This was very surprising considering the chemical composition of the fresh water and the fact that no microbiologically influenced corrosion (MIC) had been found. Testing for pitting corrosion showed no increased sensitivity of the HAZ. The Electrochemical Potentiodynamic Reactivation test (EPR test), however, was positive for the tube interior and only within the HAZ. Metallographic examinations were carried out to clarify if sensitization or intergranular attack, a type of corrosion, were the cause. The holes showed an irregular propagation which can be explained by segregation lines in the steel. It is noticeable that the holes preferably propagate in the mid-thickness region of the steel sheet. The metallographic samples showed no preferred corrosive attack along the grain boundaries (intergranular attack) and also no sensitization of the steel.