Project Details
Projekt
Nanoscopic an nanomechanical characterisation of the hydrogen influence on FGA and WEA/WEC formation
Applicants
Dr. Anna Demchenko; Professor Dr. Eberhard Kerscher
Subject Area
Mechanical Properties of Metallic Materials and their Microstructural Origins
Term
since 2024
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 523648868
Today's rolling bearings can be well designed for their application. Nevertheless, early failures repeatedly occur due to so-called white etching cracks (WEC), which are groups and networks of cracks on the flanks of which a white etching, altered fine-grained microstructure, the so-called white etching area (WEA), occurs. Similar microstructural changes are also observed in uniaxial fatigue after very high cycle fatigue in the immediate vicinity of non-metallic inclusions. In this case, one speaks of fine granular areas (FGA). These two microstructural changes have so far mostly been investigated separately from each other and independent hypotheses have been postulated. As a result, there have been hardly any comparative microstructural or chemical analyses to date. For example, the hardness has only been measured for wind turbines and there are contradictory statements regarding the influence of hydrogen on the formation of the fine grain zones and the chemical element distributions within them. The aim of the project is to investigate whether there is a common formation mechanism for the formation of FGA and WEA; based on the scanning electron microscope images and the good correlation between the plastic zone and the respective dimensions of the fine grain areas. The applicants suspect that common formation mechanisms based on dislocation rearrangement are responsible for the microstructural change within the WEA or FGA. They assume that dislocation rearrangements, dislocation cell formation and finally new grain formation already occur before the formation of fine grains, although the preliminary stages of WEAs and FGAs have hardly been investigated experimentally. In the project, precursors of WEA and FGA are therefore to be systematically generated for the first time and comprehensively observed micro- and nanostructurally as well as chemically with regard to the morphological changes in the microstructure. For the reproducible generation of precursors, the crack initiation site, which can normally only be identified after failure, should al-ready be known before the fatigue test, either by identifying critical inclusions through micro-computed tomography examinations or by introducing artificial defects. Pre-damaged samples are then analyzed using a transmission electron microscope with regard to the fine grain zones and the characteristic preliminary stages of FGA and WEA formation. The chemical element distribution in the fine grain zones will be determined using secondary ion mass spectroscopy (SIMS) and atom probe tomography (APT), whereby this technique will also be used to determine the influence of hydrogen on the formation of the fine grain zones. For this purpose, fatigue samples are pre-loaded with deuterium and analyzed after the fatigue test with regard to the deuteriumhydrogen distribution.
DFG Programme
Research Units
