Revealing the causes of the unusual mechanical behavior of B2 FeAl compounds
Iron-aluminides provide outstanding corrosion resistance and resistance in chemically aggressive environments, even at elevated temperatures up to 800°C. Due to the fact that the base materials are low cost, easily and in large quantities available, these materials could possibly substitute high-alloyed steels. Despite all the advantages, the use of iron-aluminides is limited by the low ductility and the anomalous behavior when exposed to mechanical stresses. The materials’ properties are significantly influenced by thermal history and environmental effects, which occur as hydrogen embrittlement. The aim of this collaborative project with Max-Planck Institute for Iron Research Düsseldorf is to reveal the causes of the unusual mechanical behavior of B2 iron-aluminides, focusing on the steep increase of brittle-to-ductile transition temperature (BDTT) in the range of 41 to 45 at.% aluminum content and the relation to dislocation-mediated plastic deformation. Previous investigations showed a dependence on thermal history, mechanical treatments and alloy composition. Critical factors regarding the latter include solidification, concentration of vacancies, contamination and grain size.
For determination of BDTT a novel approach, which has been developed at KIT, is used. The main goal of this approach lies in reducing the number of used specimens for investigations of BDTT to a single one. This ensures the reduction of the influence of chemical composition and microstructure in different alloy batches compared to one another.
- Evaluation of environmental effects on materials’ parameters
- Determination of the effects of heat treatments on alloys’ microstructure and mechanical properties
- Investigation of brittle-to-ductile transition temperature for different alloys
- Metallographic preparation
- Heat treatments
- Scanning electron microscopy studies of microstructure
- X-ray diffraction
- Determination of composition by 3D atom probe tomography (APT)
- Determination of the Brittle-to-ductile transition temperature (BDTT) with a novel approach