High-temperature microstructural stability of pure Ni fabricated by laser powder bed fusion using Gaussian and flat-top beam profiles

The effects of annealing on the microstructure of pure Ni fabricated by laser powder bed fusion (LPBF) were investigated using two different beam profiles: Gaussian and flat-top. The dislocations in the as-fabricated samples were predominantly arranged as statistically stored dislocations, and the low driving force resulting from the insufficient accumulation of geometrically necessary dislocations (GNDs) in the as-fabricated specimens caused minimal static recrystallization in the as-annealed specimens, despite the high dislocation density in the as-fabricated samples, particularly the Gaussian-LPBF-derived specimens. However, static recovery occurred in both the Gaussian-LPBF and flat-top-LPBF-derived specimens, with the higher number of GNDs in the former specimens causing a more prominent misorientation of dislocation boundaries than in the latter. Furthermore, migration of high-angle grain boundaries (HAGBs; misorientation >15 degrees) was not observed because of the insufficient strain gradient and the distribution of HAGBs in low-energy regions.