<p>Phase-field crystal (PFC) model was used to study the grain growth and grain boundaries of polycrystalline materials. The study reveals complex growth patterns, crack propagation, GB dislocation and the growth of various crystallites are presented. The impacts of temperature and atomic density on the growth of polycrystals with different grain sizes and grain boundaries with definite dislocations are analyzed. A morphological phase diagram with different atomic densities <i>ψ</i> and undercooling temperatures <i>ε</i> was constructed for polycrystalline grain growth to produce various grain orientations at the solid-liquid interface with crack propagation. A reduction in grain boundary area led to a decrease in the free-energy density. Moreover, grain formation and merging were simulated and analyzed as a function of grain size. Due to the disappearance of the grain boundary and the shrinking regions of the core grains, the evolution of eight-sided grains leads to a considerable reduction in the number from eight to seven and an increase in grain size. Atomic density field distributions for three to four crystallites were analyzed, and we found that the atomic density field distribution became wider and increased due to variation in atomic density and changes in grain-growth mode. These findings provide a comprehensive theoretical framework for understanding the evolution of the polycrystalline pattern across a wide range of atomic length scales and diffusive time scales.</p>