A new mechanism for laser absorption in high-reflectivity metal powder beds modified with ceramic particles

The high reflectivity of certain metal powders within the infrared laser range hinders the processability and quality of additively manufactured metals via laser powder bed fusion (L-PBF). Here, we report a new mechanism responsible for the unusually high laser absorptivity (exceeding 70%) of high-reflectivity metals such as copper and aluminum modified with micron-sized ceramic particles. It was previously thought that the increment in the absorptivity of a composite powder is ascribed to the enhanced laser multiple reflections in the powder bed, thereby enhancing the interactions between laser beams and powder particles. However, we found that the exceptionally high laser absorptivity is attributed to the synergistic effect between metal and ceramic powders, as evidenced by combining experiments with laser ray-tracing simulations. Most laser beams reflected by the metal powders are eventually absorbed by the ceramic particles, which increases the overall laser absorptivity in a nonlinear manner. In situ monitoring of thermal energy density was conducted to identify this laser absorption mechanism during sample printing. The results from x-ray computed tomography microscopy show a significant improvement in the sample quality of L-PBF high-reflectively metallic materials. Our work provides a potential way to optimize microstructures in L-PBF high-reflectivity metallic materials.