Influence of laser beam shaping on the cracking behavior of tungsten at single weld lines

Abstract

In the state of-the art, Tungsten (W) as a crack prone material in laser processing is being investigated with different approaches that influence the cooling behavior and thermomechanical conditions during processing. Investigations in the present paper analyze the application of laser beam shaping and, therefore, the adjustment and homogenization of the laser intensity input at single weld lines on pure tungsten sheets. Additionally, the laser beam size in the processing zone is varied by a factor of max. 1.9. Experiments show that the reduction of the peak laser intensities, in the range of 9,120–9,600 kW/cm² at ring-shaped beam profiles, compared to laser intensities in the region of maximal 47,200 kW/cm² at Gaussian beam profiles result in a significant crack reduction and crack avoidance. Also contributing to the crack reduction is the emerging equiaxed solidification morphology in the fusion zone at applied ring-shaped beam profiles and at the enlargement of the Gaussian beam profile. Resulting lower laser intensities at larger beam profiles at a magnification factor of 1.9 at the ring-shaped beam profile and the Gaussian beam profile show, besides the crack avoidance, a high potential for a process speed enhancement at Powder Bed Fusion of Metals using a laser-based system (PBF-LB/M) in future applications. Therefore, concerning the melt pool geometry and the emerging microstructure, the Gaussian and ring-shaped beam profile at a comparable beam diameter show similar results. Due to the severe enlargement of the melt pool width at a decent penetration depth at aspect ratios d/w < 0.5 in the conduction welding regime, adapted beam profiles can, therefore, drastically influence the cooling behavior with reduced cracking as well as enhance the process speed and eliminate process faults like keyhole porosity.