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Abstract

Hydrogen embrittlement (HE) is a collective term which summarizes different possible interactions of H with the elements of a (metallic) microstructure. Hydrogen diffuses into the strained regions of the microstructure, often along the grain boundaries, where it can promote intergranular cracking. At high H concentrations, as, e.g. in pipeline steels, additional mechanisms such as H-enhanced nucleation and mobility of dislocations play an important role. A common factor of all these mechanisms is the high mobility of H in metallic microstructures. Hence, a major step towards developing H-resistive materials is the reliable prediction of H trapping and distribution in the microstructure. In this presentation, we focus on hydrogen-enhanced decohesion (HEDE), as one of the many mechanisms of HE. Grain boundaries (GBs) provide trapping sites or act as hydrogen diffusion pathways and at the same time they are usually the weakest links in the microstructure, and this property is enhanced by the presence of H. The interaction of H with GBs depends on several parameters, such as the structure and chemistry of the interface [1,2], the H concentration, the H chemical potential, and last not least the local stress in the microstructure [3]. Therefore, for a quantitative assessment of HEDE, a generalized solution energy in conjunction with the cohesive strength as a function of hydrogen coverage is needed. To this effect we carry out density functional theory calculations H-trapping energies at special grain boundaries in ferritic steel, and of the H effect on GB cohesion. While these case studies provide valuable insights into how the abovementioned factors affect H solubility, the challenge remains to generalize the results, make them usable in a multiscale modeling framework and link them to the experimental observations. Several ongoing efforts towards this goal will be outlined [3,4,5]. References [1]A. P. A. Subramanyam, A. Azócar Guzmán, S. Vincent, A. Hartmaier, R. Janisch, Metals, 9, 291 (2019) [2]A. Guzmán, J. Jeon, A. Hartmaier, R. Janisch, Materials, 13, 5785 (2020) [3]A. Azócar Guzmán, R. Janisch, Phys. Rev. Materials, 8, 073601 (2024) [4]J. Möller, E. Bitzek, R. Janisch, H. ul Hassan, A. Hartmaier, J. Mater. Res., 33, 3750