Hydrogen-microstructure interactions in iron-based alloys at small scales: from amorphous, via nanocrystals, to polycrystals

• Applicant: Dr. María Jazmín Duarte Correa
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 318876084

Hydrogen embrittlement (HE), which is of prime concern in steels, causes material failure and thus huge economic losses. In the past, several studies focused on HE in steels, much less in amorphous alloys, and few are found for nanocrystalline materials. Despite the multiple studies on crystalline alloys, there is still a lack of fundamental understanding and exists controversy regarding the specific effects of H and the mechanisms leading to failure of the material. This project will provide knowledge on the H effects on the mechanical behavior at small length scales in Fe-based alloys with different atomic ordering. The interplay of mechanical, chemical and electrochemical properties will be studied by in-situ nanoindentation during electrochemical charging of H. The samples will consist of single phase Fe alloys with Cr contents close to that of stainless steel: amorphous Fe50Cr15Mo15C14B6, nanocrystalline and polycrystalline ferritic Fe-Cr alloys. Of special interest are the distinct deformation mechanisms: shear bands in amorphous alloys and dislocation plasticity in crystalline ones, and their respective response due to H absorption. Nanocrystalline alloys will be studied to elucidate the interplay of shear band and dislocation dominated regimes during HE. We will identify the onset of plasticity, hardness and elastic modulus of charged and uncharged samples as indicators for embrittlement. Mechanical testing at grain boundaries in crystalline alloys will evidence the H effects and possible decohesion in regions of stress concentration. Specific data on the microstructural changes will be obtained by high resolution techniques, such as transmission electron microscopy, atomic force microscopy and electron channeling contrast imaging. H concentration and permeation will be quantified by thermal desorption spectroscopy and scanning Kelvin probe measurements to correlate the mechanical and microstructural data with the H amount and location within the structure.The fundamental insights on the HE phenomena and the effects of H absorption on the mechanical response of Fe alloys, shifting from dislocation plasticity to shear banding, will be of valuable interest for the future improvement of the materials long-term stability.

• DFG Programme: Research Grants