Grain boundaries (GBs), crucial to polycrystalline materials, have been extensively studied in conventional periodic structures with rotational and translational symmetries. However, the characteristics of GBs in quasicrystals (QCs), which lack translational symmetry, remain mysterious. This study investigates the atomic configurations and formation mechanisms of GBs in two-dimensional decagonal QCs using phase-field crystal simulations. Atomic characterizations reveal that QC GBs comprise various defects, including basic and combined defects, as well as phasonic defects. The population densities of these defects increase with GB misorientation. Interestingly, the spacing of initial seeds, not causing structural changes in crystal GBs, affects defect distribution in QC GBs. The formation mechanism of QC GBs involves two stages: lattice collision and atom local rearrangement. Lattice collision occurs when two growing grains meet, inevitably leading to intergranular defects. Subsequently, atom local rearrangements—including multiatom motions around intergranular defects and phasonic flips of individual atom—act as repairs to mitigate distortions caused by lattice collisions. Phasonic flips not only reduce the number of defects but also maintain the long-range quasiperiodicity of QCs. This work elucidates the characteristics of QC GBs and their formation mechanisms, offering insights into the similarities and differences between GBs in crystals and QCs.

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• Crystal growth
• Grain boundaries
• Phase-field modeling