Band 56, Heft 10

Beryllium has an extraordinary combination of material properties such as low density, high melting point, high specific heat capacity, high Young's modulus, high hardness and low atomic number. The conventional investigation of the mechanical properties of Be and Be alloys is only possible under difficult conditions due to the material's toxicity and the resulting restrictions on sample manufacturing. These limitations are avoided, at least partly, when using a depth-sensing hardness test, also called nanoindentation, where the resulting contamination with Be dusts is limited to a controllable extent. For this work, technically pure Be from X-ray exit windows of high-performance X-ray tubes was chosen and its mechanical properties were characterized by means of nanoindentation. This contribution will focus in detail on the preparation of the material as well as the following microstructural characterization by means of light microscopy and scanning electron microscopy. The mechanical results of local nanoindentation will be correlated with the microstructure and compared with known values found in the literature.

High strength low alloy (HSLA) steels are quite crucial in weight reduction in manufacturing of vehicles and constructions with high steel thickness. Quenched and tempered S690QL HSLA steel with 700 MPa yield strength was multi-pass welded with 7 passes using MAG (Metal Active Gas) and FCAW (Flux Cored Arc Welding) methods. Heat inputs for both methods were tried to keep close to each other as much as the process parameters allowed. The effects of the welding wires and the process parameters for both methods on weld metals and heat affected zones (HAZ) were investigated. Weld metals, which were deposited by solid and cored wire electrodes, were subjected to mechanical tests and their toughness values were measured with Charphy V-notch impact test and analyzed using optical and SEM micrographs. Inclusions were present for both weld metals and HAZs. Inclusions were spherical oxides of Si, Mn and Ti for the FCAW specimen. The main microstructures of weld metals for both processes were acicular ferrite accompanied by grain boundary ferrite (GBF) and ferrite side plate (FSP) for MAG and GBF for FCAW. In coarse grain heat affected zone (CGHAZ) FCAWed specimens formed lath type martensite, which contributed to higher impact toughness compared with MAG specimens.

Cu alloys with relatively small contents of Zn and Al will oxidize heavily during heat treatment in air. Using shielding gas, however, will lead to the evaporation of Zn. A gas-tight coating, which also prevents oxidation, is required when heat treatments are carried out over several days or weeks. In the context of experiments that are aiming at the determination of diffusion parameters such long-term heat treatments are carried out. Different coatings on Cu-Zn12-Al4 (wt.%) heat-treated at 850 °C over 72 h were evaluated. A suitable system of layers consisting of an Y 2 O 3 -based and a MgO-based coating was successfully applied using the example of a heat treatment on Cu-Zn15-Al1 at 850 °C over 27 days.

After only a few weeks of use, leaks caused by pitting corrosion appeared in the weld-affected area of a fire main made of austenitic stainless steel (material number 1.4307). The quality of the used steel was checked and potential reasons for an increased susceptibility of the pipe material to pitting corrosion were searched for by examining samples of pipe sections. For this purpose, metallographic sections were prepared, etched with three different etching solutions (V2A, Beraha 2, Lichtenegger and Blöch), and examined in the light optical microscope. The examinations revealed a considerable proportion of deformation martensite and a δ-ferrite fraction of about 5 % (mainly in the cross section center) and slip lines in the edge zone. A sensitization of the material in the heat affected zone of a weld could not be observed. Deformation structures and the chromium enrichment in the δ-ferrite promote the propagation of the corrosion processes within the material. However, they cannot be related to the initiation of the pitting corrosion. Heat tinting could be observed in the weld-affected zone, and the chloride content in the water of only about 10 mg/l does not adequately explain the initiation and maintenance of pitting corrosion processes (additionally confirmed by an electrochemical examination). However, during the pipe surface examination, small black spots could also be observed on the unaffected surface. EDS analysis in the SEM and wet chemical methods identified them as microscopic manganese dioxide nodules. These deposits are an indication of microbially induced corrosion during which the microbially formed manganese dioxide, being a strong oxidant, significantly increases the stainless steel sensitivity to chloride. In the present case, this finding could be confirmed by measuring the free corrosion potential. In addition to that, indications were found suggesting that the pipe was temporarily charged with water having a higher chloride content, plausibly explaining the initiation of the pitting corrosion. The operating conditions of this pipe are characterized by stagnating water which strongly promotes the stabilization of pitting corrosion and thus represents an additional aggravating factor.