Short crack propagation near coherent twin boundaries in nickel-based superalloy

Short crack propagation near a coherent twin boundary in polycrystal nickel alloy is investigated with 3D crystal plasticity extended finite element modelling (CP-XFEM), utilising reconstructed experimentally characterised microstructures and crack path observations. Short 3D cracks at coherent twin boundaries are shown to grow on parallel (111) slip planes at very high rate so as to be an intrinsic part of the nucleation process. This is found to occur predominantly because of the stress states established by twin/parent constraint driven by the local elastic anisotropy. If elastic isotropy is modelled, crack growth is found to be non-planar and inclined to the twin boundary. The twin/parent twist angle is also found to influence local stress state, such that the actual 60 degrees twist angle gives rise to the highest local stresses, preferential crack nucleation and rapid growth parallel to the twin boundary, and the deviations from 60 degrees change the crack morphology and rate of growth.

Automated summary

Short crack propagation near a coherent twin boundary in polycrystal nickel alloy is investigated using 3D crystal plasticity extended finite element modelling (CP-XFEM), with experimentally characterised microstructures and crack path observations. The results show that short 3D cracks at coherent twin boundaries grow on parallel (111) slip planes at a very high rate, serving as an intrinsic part of the nucleation process. This is mainly due to the stress states established by twin/parent constraint driven by local elastic anisotropy. Elastic isotropy modelling leads to non-planar and inclined crack growth towards the twin boundary, and the twist angle between the twin and parent phase influences the local stress state, crack morphology, and growth rate deviation from 60 degrees.