High-temperature microstructural stability of pure Ni fabricated by laser powder bed fusion using Gaussian and flat-top beam profiles
Dennis Edgard Jodi, Tomonori Kitashima, Alok Kumar Singh, Makoto Watanabe
Abstract
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°) was not observed because of the insufficient strain gradient and the distribution of HAGBs in low-energy regions.