Effects of the orientation relationships between TCP phases and matrix on the morphologies of TCP phases in Ni-based single crystal superalloys

Observation regarding the SEM and TEM images of the precipitation and growth morphology of topologically close-packed (TCP) phase indicates that the orientation relationships between the TCP phase with different morphologies and the matrix are not that similar. Concerning with this phenomenon, via DFT calculations, the possible interface structures between the σ phase and the matrix γ, as well as the μ phase and the matrix γ have been established and discussed under different orientation relationships. The experimental characterizations and simulated calculations reveal that the orientation relationships between TCP phase and the matrix determine interplanar spacing mismatches and the interface energy of the low index dense arrangement interfaces of the two phases, while the two parameters exert influence on the growth and morphology of TCP phase. The interface energy of the σ/γ interface with (111)_γ//(001)_σ orientation is small while its interplanar spacing mismatch is large, so the TCP phase under this orientation relationship tend to take planar expansion along interface instead of growing layer by layer parallel to the plane, giving rise to plate-like morphology. However, those of the σ/γ with (110)_γ//(1–10)_σ and the μ/γ with (110)_γ//(111)_μ are just the opposite, so the TCP phases under these orientations tend to grow layer by layer instead of expand along plane, forming needle-like or rod-like morphology eventually.