Mechanical interlocking as a design-driven approach to strengthen multi-material laser powder bed fusion interface

Multi-material laser powder bed fusion (MM-LPBF) enables spatial control of material composition, offering a pathway to fabricate complex designs with localized properties. However, the performance of MM-LPBF components is limited by weak metallurgical bonding and defect formation, where differences in thermal conductivity, melting point, and solubility lead to lack of fusion, cracking, or intermetallic formation. This study investigates mechanically interlocked interfacial geometries as a strategy to improve tensile bonding strength and ductility. Tensile specimens were fabricated using 316L stainless steel and CuCrZr with three interface designs: flat interface, dovetail joint, and dual interlocked solid gyroid. Mechanical testing showed that the interlocked geometries achieved approximately 9% higher yield load and exhibiting ductile failure modes rather than brittle separation. Finite element analysis (FEA) revealed that with greater interfacial interlocking mechanism (e.g., 3D interlocked features), the predicted stress–strain response aligned more closely with experimental behavior. Microstructural analysis using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), transmission electron microscopy (TEM), and micro-computed topography (micro-CT) confirmed interface defect patterns influenced by build orientation. Results demonstrate that geometric interlocking can effectively mitigate the influence of interfacial defects, providing a practical design-based approach to enhance the mechanical integrity of MM-LPBF parts.