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Multi-material additive manufacturing holds immense potential for performance and functionality enhancement. Past research efforts primarily focused on the horizontal interface (perpendicular to the sample build direction) during the laser-powder bed fusion (LPBF) of multi-materials, whereas a few studies demonstrated that the vertical interface (parallel to the sample build direction) is in fact the main obstacle towards high-integrity multi-material fabrication in a three-dimensional space. In this work, facilitated by our own patented powder spreading device, we explored the mechanisms behind defect formation along both the horizontal and vertical interfaces during the LPBF production of 316L stainless steel and K220 copper multi-materials. High-fidelity fluid dynamics simulations were also conducted to rationalise the experimental observations. A practical process parameter optimisation approach is also proposed at the end, with the aim of mitigating those large defects currently occurring near the vertical interface.

Plastic deformation and fracture behavior of Cu/V nanoscale metallic multilayers (NMMs) were systematically investigated through in situ transmission electron microscopy testing. Two different types of interfaces: sharp interfaces and interfacial transition zones (ITZs), formed in the as-fabricated Cu/V NMMs. Upon deformation, sharp interfaces and ITZs exert distinct influences on the fracture behavior of Cu/V NMMs. Sharp interfaces can impede the crack propagation by deflecting the crack propagation and blunting the crack tip, while the ITZs can induce microcracks and facilitate the fracture process. These findings shed light on the important roles of interface structures in the deformation of a broad class of NMMs.

The competition between dislocation slip and deformation twinning in body-centered cubic (BCC) nanocrystals can be strongly influenced by the deformation conditions. In this study, we investigate the deformation of [112]-oriented BCC tungsten nanowires under different loading modes. It shows that dislocation plasticity is a predominant deformation mode under uniaxial tension, while deformation twinning prevails when non-uniaxial stress is applied. The interfaces of bending-induced twinning are composed of numerous stepwise {112} twin boundaries. These findings shed light on the deformation mechanism of BCC nanocrystals under complex loading conditions.