Influence of the laser strategy on bi-metallic interfaces printed via multi-material laser-based powder bed fusion

Metallic Multi-material Additive Manufacturing (MMAM) is an emerging research topic, with potential applications in heat exchangers, metamaterials and satellite components. In recent years, new multi-material laser powder bed fusion (PBF-LB) techniques have been developed. However, processing challenges may arise, since materials with dissimilar properties are mixed at the interfaces, which might lead to defects such as cracks. This work aims to investigate the influence of different laser scan strategies to achieve sound interfaces with different material mixing gradients. The samples, made of Inconel 718 and Invar were deposited by the patterning drums technique and were analyzed by means of optical microscopy and energy-dispersive X-ray spectroscopy (EDS) mappings and line scans. The orientation in which melt pools cross the material interface plays an important role in mixing the materials. Different orientations in subsequent layers create a certain “jagged” pattern of mixing at the interface. Sigmoid functions of Boltzmann fitted to the line scans show a significant slope steepness increase – up to 75 % – in the element count from double scan to single scan, suggesting a stronger material mixing. The double scan strategy leads to porosity at the interface and thus should be avoided. The remelt at the interface partially healed defects such as cracks but does not seem to influence the mixing width at the interface. These findings give general guidance for selecting scan strategies in MMAM depending on the desired mixing pattern at the material interface.