Regensburg 2025 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 21: Interface Controlled Properties, Nanomaterials and Microstructure Design

MM 21.6: Vortrag

Mittwoch, 19. März 2025, 17:00–17:15, H22

Characterizing the strength and stability of grain boundaries in Ni alloys by atomistic simulations — Reyhaneh Ghassemizadeh, •Daniel F. Urban, and Christian Elsässer — Fraunhofer Institute for Mechanics of Materials IWM, Freiburg, Germany

When increasing the in-service performance of engineering metallic materials, interfaces such as phase or grain boundaries (GB) may act as the weakest links. For the nickel-base superalloy Alloy 718 intergranular cracking can be a relevant damage mechanism as result of high-temperature fatigue in an oxygen-rich environment. The reliable prediction of the adhesion and mechanical stability of interfaces between two grains in a microstructure of a material from atomistic calculations remains a challenge. A possible approach to systematically address this issue is an idealized cleavage simulation analyzed in terms of the Rose-Ferrante-Smith universal binding energy relationship (UBER) which results in a measure for the ideal work of separation and the maximum tolerable normal strain. With this approach, we analyze the stability of GBs in Alloy 718 using density functional theory calculations and thereby distinguish the influence of the different alloying elements on the strength of these interfaces. Furthermore, we systematically examine the influence of oxygen at the GBs and thereby shed light on the respective segregation-induced embrittlement in polycrystalline Ni systems. Our results can be used to parametrize traction separation laws used in finite element modelling, allowing for microstructure-sensitive modelling of fatigue crack formation and growth.

Keywords: grain boundaries; Ni-base superalloy; oxygen embrittlement; density functional theory; traction separation law