Dynamic laser beam shaping by means of a deformable mirror to tailor microstructure in Directed Energy Deposition

In Laser-based Direct Energy Deposition (DED-L), the resultant mechanical properties depend on thermal cycles during deposition. Traditionally these cycles are usually optimized by tuning the laser power, traverse speed of the laser beam or material feed rate. By adapting, in real-time, the spatial power density distribution (intensity profile) in the focal spot of the laser beam, thermal cycles and thus the microstructure can be further tailored during processing. In this paper, a developed dynamic beam shaping setup, based on a deformable mirror, is used to deposit single tracks, where the high power laser intensity distribution is adapted during deposition. Melt pool monitoring showed that this setup allows to significantly change melt pool morphology during deposition. Next, microstructure analysis (EBSD) of the deposited track shows that various microstructures can be achieved, ranging from a track with larger equiaxed grains in the centre and columnar grains at the bottom and sides of the track to equiaxed grains with a strong crystallographic texture throughout the track. This proofs that the dynamic beam shaping setup is a powerful tool to steer the microstructure and therefore the functional properties of the material.