Polycrystalline γ-TiAl alloys microstructural evolution and defect analysis during LPBF process by molecular dynamics simulation

L Chen and QL Wang and BJ Gu and CL Ma and Y Yang and L Han, JOURNAL OF CRYSTAL GROWTH, 667, 128249 (2025).

DOI: 10.1016/j.jcrysgro.2025.128249

This study aims to investigate the evolution of the microstructure and defects of polycrystalline gamma-TiAl alloys during the laser powder bed fusion (LPBF) by molecular dynamics simulation. The results indicate that atoms within small grains and near grain boundaries show more active properties during laser processing, and the crystal structure of these atoms is the first to be destroyed. By observing the nucleation and growth of grains, the formation mechanism of polycrystalline gamma- TiAl alloy during LPBF process is clarified. There are two types of crystallization, one of which is the epitaxial growth of the substrate grains, while the other is the columnar growth of the molten pool grains. After crystallization, stress analysis reveals that the size effect leads to difficulty in releasing stresses in some regions which ultimately affect the nucleation and growth of the grains in those regions. In addition, the characteristics of grain boundaries result in significant stress concentration at the grain boundaries, and ultimately the grain boundaries are highly consistent with the stress contour lines. Dislocation analysis reveals that the dislocation density of the powder bed increases significantly after laser processing, and the material generates a special five-fold twins and a large number of stacking faults and twinning boundaries structures. In addition, the distribution of dislocations varies among grains of different growth types.

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