Crack-free laser welding of tungsten with the application of laser beam shaping and laser beam oscillations

In laser processing technologies such as laser beam welding and Powder Bed Fusion using a laser-based system (PBF-LB/M), tungsten remains challenging due to severe cracking caused by high cooling rates, solidification-induced stresses, and the ductile-to-brittle transition temperature. This study addresses crack suppression through laser beam shaping and laser beam oscillations. Both strategies reduce the cooling rate and alter the solidification morphology, while EBSD reveals larger and more equiaxed grains, consistent with modified solidification conditions. The combination of beam shaping and beam oscillations results in the largest grains, consistent with the greatest calculated cooling-rate reduction. These findings are supported by thermophysical G and R simulations and cooling rate calculations. Beam shaping reduces the temperature gradient G while slightly increasing the growth rate R under identical processing conditions, leading to a cooling-rate reduction of up to 40–45 %. With laser beam oscillations, 91 % of the specimens processed with a ring-core-distributed beam profile (80 % ring / 20 % core) were crack-free, compared to 80 % for a ring-shaped beam and 36 % for a Gaussian beam profile. The results demonstrate that laser beam oscillations, particularly in combination with beam shaping, enable reproducible crack-free welding of tungsten by controlling cooling conditions and solidification behavior.