Temperature- and Rate-Dependent Deformation of Additively Manufactured Copper Microlattices

The deformation behavior and mechanical properties of architected materials are determined not only by their geometry but also by the intrinsic mechanical properties of the constituent materials. In this study, we investigate the temperature and strain rate responsive deformation behavior of a 3-dimensional microarchitecture by examining the material's intrinsic deformation mechanism.<br/>We fabricate copper microlattice architectures using an additive micromanufacturing process based on localized electrodeposition in liquid. The microlattices are characterized using nano X-ray computed tomography (nano-CT), which confirms the near-ideal connectivity between nodes and struts. Microstructural characterization is performed using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), revealing that the microlattices are microcrystalline with a high fraction of twin boundaries.<br/>Furthermore, we investigate, for the first time, the mechanical properties of the copper microlattices under a wide range of strain rates (from 0.001/s to 100/s) and at various temperature conditions (cryogenic -150°C and room temperature) using a piezo-based <i>in situ</i> micromechanical testing setup inside scanning electron microscopy (SEM). The unique temperature- and rate-dependent deformation behavior of the copper microlattices is observed and explained based on the intrinsic deformation behavior of the base material (copper) obtained from micropillar compression tests performed under the same loading conditions of high strain rates and non-ambient temperatures. Notably, it is found that depending on the temperature, copper accommodates plastic deformation through either dislocation slip or mechanical twinning.<br/>This study demonstrates that complex 3-dimensional full-metal architectures can be successfully fabricated in an additive fashion at the micron scale. Furthermore, depending on the design of the architectures and their testing conditions of temperature and strain rate, these architectures exhibit unique deformation behavior that is suitable for dynamic and harsh applications.