Band 56, Heft 3

This work will present 3 typical cases of material failure with “hydrogen as the root cause of failure” which have been investigated in our SEM laboratory over the past few years: hydrogen embrittlement in spring-type straight pins, hydrogen-induced cracking in a weld and delayed cracking of a galvanized screw during a preloading test. These cases are typical for several reasons. On the one hand, the issue of “hydrogen-induced cracking” has been a regular occurrence in our laboratory for many years. On the other hand, the parameters of the examinations are always similar: In most cases, the influence of hydrogen is already suspected. This suspicion is then to be confirmed or refuted by SEM examinations of the fracture surfaces. Complex additional examinations, e. g. metallographic microstructure analysis, are generally not desired by clients due to cost concerns. In addition, our clients usually share very little information about the history of a component. With this in mind, the following examples are to be understood as a basic summary of the key results.

In fractography, different fracture surfaces are examined and described with regard to their appearance and morphology. In this context, the fracture surface carries information on the fracture event and on the material, as the morphology reflects the microstructure as well as the physical properties. In the course of this work it is show that the fractographic examination may go beyond just viewing the fracture surfaces. In addition to that, some fracture appearances are presented that are rarely encountered in practice.

The quality of technical surfaces depends significantly on the resource structures of the semi-finished product. To confirm the impact of the crystalline composition on the measuring results of scattered light technology we suggest in this article on the example of aluminium to put the measuring results in relation to the micro properties via metallographic preparation and microscopy. The main goal is to be able to determine the grain size by scattered light technology. The results determined show that a coarse grain test during an in-situ examination of aluminium is possible. The measuring method also offers the potential for the surface examination of other types of material.

When damage occurs on heat-treated components, it is initially frequently assumed that errors occurred during the heat treatment process. It could be confirmed in the course of many damage case investigations that, in principle, this might be true. However, it could also be shown that a much larger number of damage cases is caused by latent defects hidden in the component in which case the heat treatment only reveals these defects. During the heat treatment, heat and transformation stresses are unavoidable. Defects will subsequently also occur during manufacturing, after the heat treatment process, and owing to improper application conditions. Damage analysis thus not only requires a reliable measurement and examination technology but also extensive experience with materials, heat treatment procedures, and fields of application.