Volume 56, Issue 4

The properties of intermetallic titanium aluminides, such as the so-called TNM alloy, which is, owing to its high specific strength and low density, already used in the aviation and automotive sector in the temperature range from 600–800 °C, are highly dependent on the fractions and nature of the present phases. Reliable options of quantitative phase analysis are therefore indispensable. Against this background, samples of an additively manufactured TNM alloy with the composition Ti-42.1Al-4.1Nb-1.0Mo-0.1B (at. %) were metallographically analyzed and the phase fractions of the α 2 -, β 0 and γ phases were quantitatively determined by image analysis, electron backscatter diffraction, and Rietveld analysis in the course of X-ray diffraction experiments performed in this work. With regard to the fractions of the α 2 and γ phases, different results were obtained for the three methods applied which can be attributed to the characteristics of additive manufacturing and the quantitative phase analysis of multiphase samples.

The characteristic features of the structural composition of different materials manufactured by means of Selective Laser Melting of powdered material in a powder bed (AlSiMg alloy, austenitic steel, cobalt alloy, pure iron) were metallographically examined and imaged using light optical and electron microscopy as well as EBSD analysis. To date, there is not much literature available on this topic, a fact which was one of the motivations behind this contribution. The macroscopic similarities and microscopic differences between the materials will be presented as well as the relation between superstructure and microstructure. By way of example, the effect of later heat treatment on three materials in the as-built condition was examined as well. Depending on the material, very different changes in the structure can be observed.

This work evaluates different etching solutions, including Marble, Vilella, RNO and Murakami, used with the purpose of revealing secondary carbides precipitated in high chromium cast irons after heat treatments for their analysis with optical microscopy (OM) and confocal laser scanning microscopy (CLSM) and the posterior binarization of the obtained images. Etching with Marble and Murakami showed the best results for revealing secondary carbides when OM is used for the characterization. The etching parameters to reveal secondary carbides resulted to be different depending on the technique used for their evaluation, i. e. the etching time for a good phase contrast was not the same when an OM or a CLSM is used for the characterization. It was shown that the selection of the proper etchant and etching procedure is of utmost importance for the subsequent particle characterization by means of image analysis. Moreover, the results shown here intend to act as a guide for the optimization of etching parameters with the aim of finding the most suitable solution to reveal the carbides.

Owing to its excellent mechanical and thermal properties such as high strength, high hardness, and good thermal shock resistance, silicon nitride is a material suitable for forming tools. This work analyses the failure of a compaction roll made of Si 3 N 4 . One of the two ceramic rings broke during the compaction rolls' operation. Fractographic examinations have shown that very high tensile stresses occurred in the ceramic material during operation. These stresses first led to the formation of cracks and then to the total failure of the roll ring. Failure analysis has shown that roll design and clamping are of major importance. Causes for the generation of tensile stresses are shown and suggestions are made on how to ensure a safe operation of the rolls.