Volume 58, Issue 10

Among other materials, fahlores were used in the Bronze Age copper ore smelting process. These contain, apart from sulfur, arsenic and antimony. Therefore, these elements can be found in Bronze Age copper casting ingots or artifacts. In order to study the behavior of Sb more closely, two copper alloys containing 10 and 30 wt. % Sb were melted and subjected to a metallographic examination. On the one hand, microstructures with copper dendrites and homogeneous interdendritic areas primarily composed of intermetallic phase could be found. On the other hand, at higher Sb concentrations, first Cu 3 Sb precipitated which, in turn, transformed to Cu 10 Sb 3 upon cooling. The crystals in these microstructures were characterized by numerous parallel cracks. No further phases were observed by XRD.

Fe-Nd-B powders were processed by additive manufacturing using laboratory scale selective laser melting to produce bulk nanocrystalline permanent magnets. The manufacturing process was carried out in a specially developed process chamber under Ar atmosphere. This resulted in novel types of microstructures with micrometer scale clusters of nanocrystalline hard magnetic grains. Owing to this microstructure, a maximum coercive field strength (coercivity) μ 0 H c of 1.16 T, a remanence J r of 0.58 T, and a maximum energy product (BH) max of 62.3 kJ/mm 3 could, for example, be obtained for the composition Nd16.5-Pr1.5-Zr2.6-Ti2.5-Co2.2-Fe65.9-B8.8.

Chip formation is an important indicator of machining processes. Statistical characterization of machining chips’ geometric features can offer crucial information for evaluating the stability and productivity of the machining processes. In abrasive machining processes, an abundance of small chips are produced by the vast number of abrasives exposed to the cutting surfaces. Geometric features of abrasives, such as shape, dimension, and distribution, may be hierarchically passed on to the chips. Similar to those of the abrasives, geometric features of the chips may also vary to a certain extent and conform to some statistical distribution. To verify these characteristics, a metallographic preparation method in connection with chips formed in abrasive machining processes is proposed in this study. Challenges in collecting and segmenting chips have been successfully overcome through several steps using ultrasonic bath cleaning and powder cold embedding methods. Finally, a considerable amount of chips was formed and uniformly embedded in a resin mold, ready for microscopic characterization.

Exhaust stack liners of a test rig for gas turbine burners failed locally by ruptured fasteners and fallen-off liner plates. Misalignment of the plating relative to each other and relative to their fasteners caused restraint of the expanding and shrinking liner plates upon start-up and shutdown of the burner rig. The fastening holes of the failed liner plates were not concentric, but misaligned relative to each other and relative to their fastener bolts. This exerted a shear loading on the threads of the fastening bolts, which in turn caused a mean stress shift and damaged the threads of the fasteners by nicking. So pre-loaded, the fastening bolts were not able to withstand the vibratory loads from the flowing exhaust gases and failed due to fatigue.