Strengthening of 3D printed Cu micropillar in Cu-Ni core-shell structure

Direct printing of complex 3D structures at the nano-and microscale is a promising technique for MEMS devices, small-scale sensors, and actuators. So far, most studies have been focused on printing copper (Cu) structures due to the high Coulombic efficiency compared to other conductive metals such as plat-inum. However, Cu suffers from low material strength, low modulus, and high strain-rate sensitivity. This work introduces a unique Cu-Ni core-shell structure for improved strength. A 3D additive-micromanufacturing technique based on localized electrodeposition was utilized to fabricate dog -bone-shaped Cu micropillars with submicron resolution. These pillars were subsequently coated with Ni by pulse-reverse electrodeposition. A combination of in-situ micropillar compression at various strain rates (0.001-500 s-1) and finite element simulations revealed remarkable strengthening in the Ni-coated Cu micropillar. Data obtained from both experiments and simulations were in good agreement, suggest-ing the strengthening was dominated by interface characteristics, stress redistribution, and geometrical effects. Furthermore, the study demonstrates that shape and dimension of the 3D-printed objects can be retained while increasing their strength drastically. These findings can be extended to other material sys-tems and provide a pathway to develop strong and tough composites and metamaterials at multiple length scales for future applications.(c) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).