Focus of the Project:

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This project aims to develop a theoretical framework for understanding oxide-controlled dwell fatigue crack growth in γ'-strengthened nickel-based superalloys. Specifically, the study investigates the interplay between externally applied loads and variations in the dispersion of γ' particles, assessing their impact on the kinetics of grain boundary oxide growth.

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Methodology:

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To model the evolution of the stress state near a crack at elevated temperatures, a dislocation-based viscoplastic constitutive description for high-temperature deformation is employed. Additionally, a multicomponent mass transport formulation is utilised to simulate the formation and evolution of an oxide wedge ahead of the crack tip, assuming the operation of stress-assisted vacancy diffusion.

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Key Findings:

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Simulation results underscore the significant influence of a fine γ' size distribution on the predicted flow stress of the material, which in turn affects the relaxation behaviour in the vicinity of the crack tip and the oxide wedge. Furthermore, the simulations demonstrate that a fine γ' size distribution leads to reduced oxide growth rates, following a parabolic trend, when compared to a bimodal dispersion.