To address the critical applications of heterogeneous structures involving nickel-based superalloys (IN718) and copper alloys (CuSn10) under extreme operating conditions, and to address the limitations of traditional joining techniques in terms of interfacial brittleness and geometric constraints, this study employs Laser Powder Bed Fusion (LPBF) technology, specifically multi-material LPBF (MM-LPBF). By precisely melting IN718 and CuSn10 powders layer by layer, the study directly fabricates multi-material IN718/CuSn10 joint specimens, thereby simplifying the complexity of traditional joining processes. The research systematically investigates the interfacial microstructure and mechanical property evolution laws and underlying mechanisms. It reveals that sufficient element diffusion and hardness gradients are present at the IN718/CuSn10 interface, indicating good metallurgical bonding. However, due to significant differences in thermophysical properties, cracks inevitably appear at the interface. Mechanical property tests indicate that the strength of the IN718/CuSn10 joint specimens falls between that of IN718 and CuSn10, but with lower elongation, and fractures primarily occur at the interface. This research provides theoretical support for establishing a process database for LPBF formed of nickel–copper heterogeneous materials, advancing the manufacturing technology of aerospace multi-material components.

The dissimilar combination of NiTi shape memory alloy and Ti6Al4V titanium alloy offers superelasticity, biocompatibility and high specific strength, showing broad application prospects in aerospace and medical fields. However, when fabricating NiTi/Ti6Al4V composite components by multi-material laser powder bed fusion (MM-LPBF), brittle cracks or even complete delamination easily occur at the interface. In this paper, without relying on intermediate interlayer materials, we innovatively propose a root-inspired three-dimensional bio-interlocking interface structure. By means of macroscopic three-dimensional geometric interlocking, the crack propagation path and load transfer mode are forced to change. Using the branching angle (45°, 60°) and the structural size multiplier (1.2, 1.5) as variables, the influence of the bio-inspired geometric parameters on the interfacial forming quality, microstructure and mechanical properties was systematically investigated. The results show that the branching angle is the primary factor determining the performance. The 45° low-angle branched specimens exhibit overall brittle delamination along the flat metallurgical reaction interface under shear loading, with an average shear strength of only 17.47 MPa. In contrast, the 60° high-angle branched specimens, owing to their larger normal embedding depth, exhibit a failure mode transitioning to a mixed mode that includes crack deflection, branch shearing and plastic tearing of the Ti6Al4V matrix. Although TEM confirms that a continuous Ti₂Ni brittle phase still exists at the interface, the optimised 60–1.5 structure increases the average shear strength to 128.37 MPa, which is more than six times higher than that of the 45–1.2 group (17.47 MPa). This “geometrical constraint toughening” strategy provides a new paradigm for the interfacial strengthening of dissimilar metals without relying on metallurgical modification.