Modeling composition-dependent melt dynamics and defect formation in multi-material additive manufacturing

Multi-material laser powder bed fusion (PBF-LB/M) enables the fabrication of components with tailored properties for advanced applications. However, large differences in thermophysical behavior between alloys such as Cu and SS316L introduce processing challenges, including lack of fusion, porosity, and thermal cracking at material interfaces. In this study, a coupled Discrete Element Method-Computational Fluid Dynamics (DEM-CFD) framework with a Volume of Fluid (VOF) methodology is developed to investigate melt pool dynamics, interfacial mixing, and solidification in laser powder bed fusion of Cu-SS316L. The model accounts for temperature and composition dependent thermophysical properties, diffusion-driven species transport, and laser–material interaction through a ray-tracing approach. Experimental validation is conducted to support the numerical findings. Simulations reveal that high Cu content results in smaller melt pools and lack of fusion defects due to Cu's high reflectivity and thermal diffusivity, whereas SS316L rich regions produce larger melt pools, reducing fusion defects but increasing keyhole porosity risk. At the Cu-SS316L interface, asymmetric melting and rapid solidification on the Cu side limit mixing, forming sharp diffusion boundaries. Steep thermal gradients across the interface induce differential thermal expansion, leading to thermal crack formation, particularly under high energy input. To mitigate such defects, a material grading strategy is proposed to smooth thermal gradients and reduce residual stresses. The proposed numerical framework offers critical insights into the mixing mechanisms at dissimilar interfaces for optimizing the multi-material PBF-LB/M process.