Band 56, Heft 7

When nanoindentation tests are performed on aluminum alloys, pile-ups can be observed in the area of the plastic deformation of the elastic-plastic indent. These pile-ups may have an impact on the actual contact area between indenter and sample and hence, have a significant influence on the measured mechanical properties. This work analyzed the pile-up behavior of a precipitation hardening (AA2024) and a solid solution strengthened (AA5182) Al wrought alloy in their coarse-grained and the ultrafine-grained condition. Here, the residual indents were examined using differential interference contrast light microscopy and scanning electron microscopy with secondary electrons as well as with electron backscatter diffraction capability. Micrographs of the hardness impressions were discussed in terms of the material pile-ups with respect to quality (deformation behavior) and quantity (actual contact area).

The microstructure of a duplex stainless steel, e. g. 1.4462 (X2CrNiMoN22 – 5 – 3), is half austenite and half δ-ferrite. The challenge for the metallographer is to clearly determine the austenite / δ-ferrite quantity ratio, also in the weld metal and in the heat-affected zone and to find clear evidence for the presence of possible, detrimental precipitations of intermetallic phases. This is all the more difficult as both – austenite and δ-ferrite – appear light under the microscope when using standard etchants and as twins, which are typical of austenitic microstructures in the as-rolled condition, do not form in the weld metal. This work will thus present preparation methods which allow for a clear distinction of the microstructural constituents, austenite and δ-ferrite, as well as for a clear determination of the quantity ratios.

Preparation of oxidized steel samples demands special attention, due to the heterogeneous composition combining hard and brittle with soft and ductile phases. Samples of various steels taken from the hot rolling process at voestalpine Stahl GmbH as well as samples oxidized in a horizontal tube furnace under controlled atmosphere are examined. Suitable mounting techniques, including the use of taper section angles to achieve increased depth resolution, and preparation parameters for reproducible and satisfactory results are presented, backed by images taken during various stages of grinding and polishing.

Steel 1.4841 was tested as a possible reactor material for a cracking process of anthropogenic resources under simulated laboratory conditions at 680 °C. The gas atmosphere present in this process contains HCl as well as H 2 S. In order to evaluate the corrosion behavior, metallographic sections were prepared from the corroded samples. The preparation for the SEM/EDS examination had to be performed under exclusion of water, as otherwise the readily water-soluble metal chlorides would not have been detected. A layered, porous structure of the corrosion products (oxides and sulfides of Cr) could be observed. The lowermost layer contains chromium and iron chlorides. Nickel could not be found in any of the corrosion products. In order to estimate the long-term resistance, aging tests were performed at 680 °C in an inert atmosphere for up to 1600 h before the actual corrosion tests. The formation of Cr 23 C 6 and also of Ϭ phase could be evidenced by TEM. Compared to the non-aged samples, the chromium depletion caused by aging resulted in slightly increased corrosion rates.