Dynamic cryo-mechanical properties of additively manufactured nanocrystalline nickel 3D microarchitectures

Template-assisted electrodeposition is a promising microscale additive manufacturing technique allowing to deposit pure metals with high resolution. To allow the application-relevant design of metamaterials, it is necessary to establish microstructure-mechanical property relationships under extreme conditions. In this work, a novel process based on two-photon lithography was used to synthesize arrays of nanocrystalline nickel micropillars and complex microlattices. This allowed high throughput mechanical testing using a newly developed in situ nanoindenter at unprecedented combination of cryogenic temperatures (160 to 300 K) and strain rates (0.001 to 500 s⁻¹). Strain rate sensitivity was found to increase from ∼ 0.004 at 300 K to ∼ 0.008 at 160 K. Thermal activation analysis showed a decrease in activation volume from 122b³ at 300 K to 45b³ at 160 K and an activation energy of 0.59 eV in line with collective dislocation nucleation as the rate limiting mechanism. Transmission Kikuchi Diffraction allowed quantifying microstructural changes during deformation. As such, a deformation map along with the responsible deformation mechanisms has been ascertained for additively micromanufactured nanocrystalline nickel at unique combinations of extreme temperatures and strain rates. Further, rate-dependent compression of microlattices and complementary finite element simulations using the results from micropillars as constitutive models exemplified the promise of such metal microarchitectures in space and aviation applications.