Ultra-strong bond interface in additively manufactured iron-based multi-materials

Functional multi-material additive manufacturing (AM) provides a novel way to process components with high structural complexity, functionality and good bond strength. In addition to laser processing parameter, here we investigated the effect of the elemental composition of materials on the interfacial bond strength through laser powder bed fusion (LPBF) of two-type iron-based multi-materials. The interfacial melting strategy is optimised for achieving reliable bonding interface, and the bonding reliability was evaluated by multiple mechanical testing. The interfacial microstructural analysis suggests that the intense interfacial elements diffusion contributes to metallurgical bonding. Gradient on the grain size distribution is observed concurrently with low-micro strain in bond regions. Mechanical performance is evaluated by static tensile and flexural tests, alongside with dynamic tension fatigue testing. The results reveal that the interfacial bond strength (>689 MPa) exceeds the fracture strength of substrate materials, suggesting an interface strengthening behaviour. Furthermore, an ultra-strong bond interface was revealed by tension fatigue tests, which owes to Marangoni circular flows and intense elements inter-diffusion, together with a low interfacial strain. The findings shed light on AM of highly reliable multi-material components under harsh service conditions with cyclic and alternating loads.