Laser Powder Bed Fusion (LPBF) offers significant advantages in the fabrication of complex metallic structures and the improvement of material usage. However

conventional Gaussian laser sources offer several limitations

including uneven energy distribution and small spot size

resulting in narrow processing window and low forming efficiency. This study employs a donut laser beam with a more uniform energy distribution using a beam shaping technology to fabricate IN939 nickel-based superalloy by investigating the microstructure regulation. The results indicate that

compared to the Gaussian laser

the donut laser beam effectively mitigates keyhole defects through a broader processing window. The melt pool aspect ratio was reduced to 0.14

and the heat transfer mode transitioned from keyhole mode to conduction mode. Simulation results show a significant reduction in the melt pool  temperature gradient

with peak velocity decreasing by 37%

leading to more stable melt pool dynamics. Additionally

IN939 samples fabricated using the donut laser beam exhibited columnar grains preferentially oriented along the 001 direction

with a distinct cubic texture (texture strength reaching 12.59). The proportion of low-angle grain boundaries was 57.1%

which benefits from mitigating crack defects. The surface roughness of the samples was improved

with Ra decreasing from 5.8 μm to 4.0 μm

thereby significantly improving the overall forming quality by employing the donut laser beams.