Investigation of ductility-regulating factors in body-centered cubic (bcc) steels strengthened by B2-(Ni,Fe)Al intermetallic precipitates

• Applicant: Professor Javad Mola, Ph.D.
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 562780065

The Al addition to steels favors the formation of intermetallic phases. Body-centered cubic (bcc) steels containing Al and Ni are capable of forming B2-ordered intermetallic precipitates, which could then be represented as (Fe,Ni)Al. In spite of their positive contribution to the strength, B2 precipitates result in a loss of tensile ductility at deformation temperatures near room temperature. This offsets the lightweighting effect of Al and limits the application of Al-added steels. The proposed project aims to address this downside of Al-added bcc steels by controlled formation and manipulation of B2 precipitates in ferritic stainless steels followed by tensile tests and post-mortem characterizations. Disrupting the inherent cube-on-cube orientation relationship between the bcc matrix and B2 precipitates and facilitating the plastic deformation of B2 precipitates will be among factors to influence the overall ductility of the steels. The ability of B2 to undergo plastic deformation will be controlled by adjusting the loading direction in single-crystalline ferrite - to regulate the Schmid factor - as well as by modifying the deformation temperature and B2 size. The project will also investigate conditions for the occurrence of cleavage in Al-added steels, to determine if cleavage can take place even if Al remains fully in solid solution. For a phase-specific analysis of the evolution of lattice strains and micro-strains during uniaxial tensile tests, in-situ high-energy X-ray diffraction (HEXRD) experiments are planned. The lattice strains and micro-strains from such measurements will correlate with the stress and fault density, respectively. The HEXRD experiments will therefore help assess the stress partitioning between the ferritic matrix and B2 precipitates and determine the onset of plastic deformation in B2. By studying potential contributors to the embrittlement in isolation, their relative importance will be clarified. This understanding will offer the prospect of lightweight resource-efficient high-strength stainless steels, which are at the same time ductile.

• DFG Programme: Research Grants