Humidity-Dependent Flaw Sensitivity in the Fracture Toughness of 3d-Printed Nano-Ceramics

Abstract

3D-printed nano-architected ceramic meta-materials currently emerge as a class of lightweight materials with exceptional strength and stiffness. However, their application is hampered by the lack of knowledge on their mechanical reliability. Characteristics like the fracture toughness and their dependency on environmental conditions are unknown. We herein present nano-indentation pillar splitting as a straight-forward method to measure fracture toughness, elastic modulus, and hardness of 3D-printed nano-ceramics. We show that two photon polymerization-derived pyrolytic carbon achieves 500% increased fracture toughness over macroscopic forms of vitreous carbon, with values up to 3.1 MPam 0.5 . However, experiments at different humidity levels reveal that only few, nano-meter-sized, surface cavities can cause embrittlement from liquid diffusion, which promotes crack propagation due to capillary pressure. While comparable effects are unknown in macro-size ceramics, this study demonstrates that reliability and durability of micro- and nano-architected ceramic meta-materials requires toughening design approaches which focus on size-dependent surface effects.

Keywords: Two-Photon Polymerization Direct Laser Writing, Pyrolytic Carbon, Fracture Toughness, Pillar Splitting, Humidity