Speaker
Description
Hydrogen (H) is the most abundant element in the Universe. It has a great potential to replace the C-based fuels as a more sustainable energy solution. In order to support and implement this transition towards a more sustainable H economy, understaning the interaction of H with its surrounding infrastructure requires immediate attention. H embrittlement (HE) is a phenomenon that causes abrupt loss in the load bearing capacity of large engineering structures in the presence of H. Its limited understanding poses a hurdle for the transition to a H based economy. High strength steels are particularly prone to HE where even less than 1 part per million by weight (ppmw) H is sufficient to dramatically degrade the mechanical properties [1]
Medium Mn steels consisting of a dual-phase, austenite-ferrite microstructure have been employed for its enhanced transformation induced plasticity (TRIP) effect to achieve an improved strength-ductility combination [2]. However, its multiphase microstructure with difference in H solubilities and diffusivities makes HE studies on this material system challenging. A recent study elucidated to the presence of strong H trapping sites with an activation energy of up to 50 kJ/mol in such steels, hinting towards H trapping at the austenite-ferrite phase boundaries (PBs) [3].
Here, a medium Mn steel (0.2C-10Mn-3Al-1Si) is heat treated to produce a microstructure with a high density of PBs which will enable us to bypass the need for site specific specimen preparation for APT. Additionally, the microstructure revealed an approximately equal fraction of semi-coherent and incoherent PBs. We investigate and visualize interaction of H by systematically probing vacancy clusters, dislocations, and austenite-ferrite PBs via atom probe tomography (APT).
References
[1] B. Sun, W. Lu, B. Gault, R. Ding, S.K. Makineni, D. Wan, C.-H. Wu, H. Chen, D. Ponge, D. Raabe, Chemical heterogeneity enhances hydrogen resistance in high-strength steels, Nature Materials (2021).
[2] B. Sun, Y. Ma, N. Vanderesse, R.S. Varanasi, W. Song, P. Bocher, D. Ponge, D. Raabe, Macroscopic to nanoscopic in situ investigation on yielding mechanisms in ultrafine grained medium Mn steels: Role of the austenite-ferrite interface, Acta Materialia 178 (2019) 10-25.
[3] B. Sun, W. Krieger, M. Rohwerder, D. Ponge, D. Raabe, Dependence of hydrogen embrittlement mechanisms on microstructure-driven hydrogen distribution in medium Mn steels, Acta Materialia 183 (2020) 313-328
