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

In laser processing, such as laser beam welding and Powder Bed Fusion using a laser-based system (PBF-LB/M), tungsten still remains a challenging material due to its cracking phenomena. As the cracking of tungsten in a laser-based process emerges from the high cooling rates, the resulting tensions during solidification, and the involved ductile-to-brittle temperature, this paper addresses the crack elimination with the application of laser process-based approaches such as laser beam shaping and laser beam oscillations. Both strategies show a reduction in the cooling rate, shown with the emergence of an overall bigger grain size compared to the application of a Gaussian beam shape, and also an influence on the solidification morphology. A more pronounced equiaxed grain structure in the fusion zone and a drastic reduction of the oriented grain structure towards the fusion line can be observed. When applying laser beam oscillations, 91 % of 55 parameter combinations using a ring-core-distributed beam shape (with 70 % in the ring and 30 % in the core) resulted in crack-free specimens, while 80 % of 108 tested parameter combinations using a ring-shaped beam profile, and only 36 % of 36 test parameter combinations using a Gaussian beam profile led to crack-free specimens. Therefore, applying laser beam oscillations allows for a reproducibly crack-free manufacture of single weld lines on tungsten sheets.