Volume 54, Issue 5

Vanadium silicide alloys are potentially interesting high temperature materials, since they combine high mechanical strength at temperatures of up to 1 000 °C with a low density. In this study, the microstructures of innovative V-Si-B high temperature materials are examined using different analytical methods. The selected V-9Si-13B model alloy was manufactured using a powder metallurgical process route as well as an ingot metallurgical process. The alloys show a vanadium solid solution phase as well as the high-strength silicide phases V 3 Si and V 5 SiB 2 . Especially for the powder metallurgically fabricated alloy, showing finely dispersed phases, the quantification of microstructural constituents is difficult. The phases, however, can be separated from one another via computer tomography.

This work presents the quantitative evaluation of the gamma-prime phase for two nickel-based alloys which contain different proportions of this phase. Alloy 617 mod. was chosen here as an example for nickel alloys with a small volume fraction of the gamma-prime phase, while Alloy 263 was chosen as a material with a higher proportion. The examinations are performed in the scanning electron microscope (SEM) with high resolution as well as with a transmission electron microscope (TEM). The methods of quantitative recording are discussed. The results of the SEM and TEM analyses are compared and discussed. Several etching techniques were applied for the sample preparation.

Various color etching techniques are by now well introduced and complement the standard preparations in many metallographic laboratories or, in the case of some material groups, even replace them. However, the interpretation of the thus obtained micrographs requires a certain experience. In order to recognize and utilize the benefits of color etching, the preparation as well as the evaluation should be practiced under supervision. Misinterpretations can thus be avoided. On the one hand, color etchings according to Klemm can help to better recognize carbide precipitations on the grain boundaries as well as segregations in unalloyed and low alloyed steels, cast iron, and in tool and quenched and tempered steels (Klemm I). On the other hand, these etchings (Klemm II and Klemm III) are also very well suited for copper alloys and solderings. They serve to reveal various solid solution types, separations (segregations), diffusion zones, and fine precipitations.