Interface Behavior in Multi-Material Additive Manufacturing: An Experimental Study of SS316L and IN718

Directed energy deposition using laser metal deposition (LDED) enables the fabrication of multi-material components with site-specific properties; however, the mechanical reliability of bimetallic interfaces remains insufficiently understood, particularly when the interface is oriented parallel to the loading direction. This study experimentally investigates the mechanical response and fracture behavior of LDED-fabricated SS316L/IN718 bimetallic structures with an interface parallel to the applied load. In contrast to the commonly studied 50/50 compositional configuration, specimens with 30/70 and 70/30 volume fractions were also produced to evaluate the influence of material distribution on failure mechanisms.While fracture is generally expected to initiate in the SS316L region due to its lower strength, several specimens exhibited crack initiation within the IN718 region. Microstructural analysis revealed Nb segregation in the IN718 adjacent to the interface, which is believed to enhance local strengthening in SS316L while simultaneously reducing the structural stability of IN718, thereby promoting crack initiation on the IN718 side. The results demonstrate that compositional ratio and segregation-induced microstructural heterogeneity strongly influence load transfer and fracture location in bimetallic systems.This work represents a step toward a mechanistic understanding of interface-parallel loading in additively manufactured bimetallics. Future work will focus on developing a finite element model capable of capturing the coupled effects of composition gradients, microstructural evolution, and interfacial behavior to predict the mechanical response of multi-material AM structures.